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1. Android Development
1.1. Android Operation System
Android is an operating system based onLinuxwith aJavaprogramming interface. It
provides tools, e.g. a compiler, debugger and a device emulator as well as its own Java
Virtual machine (Dalvik Virtual Machine - DVM).Androidis created by the Open
Handset Alliance which is lead by Google.
Android uses a special virtual machine, e.g. the Dalvik Virtual Machine. Dalvik uses
special bytecode. Therefore you cannot run standard Java bytecode on Android.
Android provides a tool "dx" which allows to convert Java Class files into "dex" (Dalvik
Executable) files. Android applications are packed into an .apk (Android Package) file bythe program "aapt" (Android Asset Packaging Tool) To simplify development Google
provides the Android Development Tools (ADT) forEclipse. The ADT performs
automatically the conversion from class to dex files and creates the apk during
deployment.
Android supports 2-D and 3-D graphics using the OpenGL libraries and supports data
storage in aSQLitedatabase.
EveryAndroidapplications runs in its own process and under its own userid which isgenerated automatically by the Android system during deployment. Therefore the
application is isolated from other running applications and a misbehaving application
cannot easily harm other Android applications.
1.2. Important Android components
An Android application consists out of the following parts:
Activity - Represents the presentation layer of an Android application, e.g. ascreen which the user sees. An Android application can have several activities and
it can be switched between them during runtime of the application.
Views - The User interface of an Activities is build with widgets classes which
inherent from "android.view.View". The layout of the views is managed by
"android.view.ViewGroups".
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Services- perform background tasks without providing an UI. They can notify
the user via the notification framework in Android.
Content Provider- provides data to applications, via a content provider your
application can share data with other applications. Android contains a SQLite DB
which can serve as data provider
Intentsare asynchronous messages which allow the application to request
functionality from other services or activities. An application can call directly a
service or activity (explicit intent) or ask the Android system for registered
services and applications for an intent (implicit intents). For example the
application could ask via an intent for a contact application. Application register
themself to an intent via an IntentFilter. Intents are a powerful concept as they
allow to create loosely coupled applications.
Broadcast Receiver - receives system messages and implicit intents, can be usedto react to changed conditions in the system. An application can register as a
broadcast receiver for certain events and can be started if such an event occurs.
Other Android parts areAndroid WidgetsorLive FoldersandLive Wallpapers. Live
Folders display any source of data on the homescreen without launching the
corresponding application.
1.3. Security and permissions
Android defines certain permissions for certain tasks. For example if the application
want to access the Internet it must define in its configuration file that it would like to
use the related permission. During the installation of an Android application the user
get a screen in which he needs to confirm the required permissions of the application.
1.4. AndroidManifest.xml
An Android application is described the file "AndroidManifest.xml". This file must
declare all activities, services, broadcast receivers and content provider of the
application. It must also contain the required permissions for the application. For
example if the application requires network access it must be specified here.
"AndroidManifest.xml" can be thought as the deployment descriptor for an Android
application.
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The "package" attribute defines the base package for the following Java elements. It also
must be unique as the Android Marketplace only allows application for a specfic package
once. Therefore a good habit is to use your reverse domain name as a package to avoid
collisions with other developers.
"android:versionName" and "android:versionCode" specify the version of your
application. "versionName" is what the user sees and can be any string. "versionCode"
must be an integer and the Android Market uses this to determine if you provided a
newer version to trigger the update on devices which have your application installed.
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You typically start with "1" and increase this value by one if you roll-out a new version of
your application.
"activity" defines an activity in this example pointing to the class
"de.vogella.android.temperature.Convert". For this class an intent filter is registeredwhich defines that this activity is started once the application starts (action
android:name="android.intent.action.MAIN"). The category definition (category
android:name="android.intent.category.LAUNCHER" ) defines that this application is
added to the application directory on the Android device. The @ values refer to resource
files which contain the actual values. This makes it easy to provide different resources,
e.g. strings, colors, icons, for different devices and makes it easy to translate
applications.
The "uses-sdk" part of the "AndroidManifest.xml" defines the minimal SDK version
your application is valid for. This will prevent your application being installed on devices
with older SDK versions.
1.5. R.java, Resources and Assets
The directory "gen" in an Android project contains generated values. "R.java" is a
generated class which contains references to resources of the "res" folder in the project.
These resources are defined in the "res" directory and can be values, menus, layouts,
icons or pictures or animations. For example a resource can be an image or an XML files
which defines strings.
If you create a new resources, the corresponding reference is automatically created in
"R.java". The references are static int values, the Android system provides methods to
access the corresponding resource. For example to access a String with the reference id
"R.string.yourString" use the method getString(R.string.yourString)); Please do not try
to modify "R.java" manually.
While the directory"res" contains structured values which are known to the Android
platform the directory "assets" can be used to store any kind of data. In Java you can
access this data via the AssetsManager and the method getAssets().
1.6. Activities and Layouts
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The user interface for Activities is defined via layouts. Layouts are at runtime instances
of "android.view.ViewGroups". The layout defines the UI elements, their properties and
their arragement. UI elements are based on the class "android.view.View". ViewGroup is
a subclass of View A and a layout can contain UI components (Views) or other layouts
(ViewGroups). You should not nestle ViewGroups to deeply as this has a negativ impact
on performance.
A layout can be defined via Java code or via XML. You typically uses Java code to
generate the layout if you don't know the content until runtime; for example if your
layout depends on content which you read from the internet.
XML based layouts are defined via a resource file in the folder "/res/layout". This file
specifies the view groups, views, their relationship and their attributes for a specific
layout. If a UI element needs to be accessed via Java code you have to give the UI
element an unique id via the "android:id" attribute. To assign a new id to an UI element
use "@+id/yourvalue". By conversion this will create and assign a new id "yourvalue" to
the corresponding UI element. In your Java code you can later access these UI elements
via the method findViewById(R.id.yourvalue).
Defining layouts via XML is usually the preferred way as this separates the
programming logic from the layout definition. It also allows to define different layouts
for different devices. You can also mix both approaches.
1.7. Activities and Lifecyle
The operating system controls the life cycle of your application. At any time the Android
system may stop or destroy your application, e.g. because of an incoming call. The
Android system defines a life cycle for an activities via pre-defined methods. The most
important methods are:
onSaveInstanceState() - called if the activity is stopped. Used to save data so that
the activity can restore its states if re-started
onPause() - always called if the Activity ends, can be used to release ressource or
save data
onResume() - called if the Activity is re-started, can be used to initiaze fields
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The activity will also be restarted if a so called "configuration change" happens. A
configuration change for examples happens if the user changes the orientation of the
device (vertical or horizontal). The activity is in this case restarted to enable the Android
platform to load different resources for these configuration, e.g. layouts for vertical or
horizontal mode. In the emulator you can simulate the change of the orientation via
CNTR+F11.
You can avoid a restart of your application for certain configuration changes via the
configChanges attribute on your activity definition in your AndroidManifest.xml. The
following activity will not be restarted in case of orientation changes or position of the
physical keyboard (hidden / visible).
1.8. Context
The class android.content.Context provides the connections to the Android system. It is
the interface to global information about the application environment. Context also
provides the method which allows to receive Android services, e.g. theLocation Service.
As Activities and Services extend the class "Context" you can directly access the context
via "this".
2. Installation
The following assume that you have alreadyEclipse installed. For details please
seeEclipse Tutorial .
2.1. Android SDK
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Download the Android SDK from the Android homepage underAndroid SDK download.
The download contains a zip file which you can extract to any place in your file system,
e.g. I placed it under "c:\android-sdk-windows". Avoid using spaces in the path name
otherwise you may experience problems later.
2.2. Eclipse
Use theEclipse update managerto install all available plugins for the Android
Development Tools (ADT) from the URLhttps://dl-ssl.google.com/android/eclipse/.
2.3. Configuration
In Eclipse open the Preferences dialog via Windows -> Preferences. Select Android and
enter the installation path of the Android SDK.
Select Window -> Android SDK and AVD Manager from the menu.
Select "Available packages" and open the "Third Party Add-ons". Select the Google API
10 (Android 2.3.4) version of the SDK. We are using the Google version as this includes
also the Google Maps which we might want to use later at a certain point.
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Press "Install selected" and confirm the license for all package. After the installation
restart Eclipse.
2.4. Android Source Code
The following step is optional.
During Android development it is very useful to have the Android source code available
as Android uses a lot of defaults.
Haris Pecomaintains plugins which provides access to the Android Source code code.
Use the Eclipse update manager to install the Android Source plugin from the following
update site: "http://adt-
addons.googlecode.com/svn/trunk/source/com.android.ide.eclipse.source.update".
More details can be found on theproject website.
3. Create an Android Emulator Device
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The Android tools include an emulator. This emulator behaves like a real Android device
in most cases and allow you to test your application without having a real device. You
can emulate one or several devices with different configurations. Each configuration is
defined via an "Android Virtual Device" (AVD).
To define an AVD press the device manager button, press "New" and enter the following.
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We will select the box "Enabled" for Snapshots. This will make the second start of the
virtual device much faster.
At the end press the button "Create AVD".This will create the device and display it under
the "Virtual devices". To test if your setup is correct, select your device and press "Start".
After (a long time) your device should be started.
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4. Error handling
Things are not always working as they should be. Several users report that get the
following errors:
1. Project ... is missing required source folder: 'gen'
2. The project could not be built until build path errors are resolved.
3. Unable to open class file R.java.
To solve this error select from the menu Project -> Clean.
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If you having problems with your own code you can use the LogCat viewer as described
inLogCat Viewer .
5. Your first Android project
5.1. Create Project
This app is also available on the Android Marketplace. Search for "vogella" for find this
example.
Select File -> New -> Other -> Android -> Android Project and create the Android
project "de.vogella.android.temperature". Enter the following.
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Press "Finish". This should create the following directory structure.
While "res" contains structured values which are known to the Android platform the
directory "assets" can be used to store any kind of data. In Java you can access this data
via the AssetsManager and the method getAssets().
5.2. Two faces of things
The Android SDK allows to define certain artifacts, e.g. strings and UI's, in two ways, via
a rich editor and directly via XML. The following description tries to use the rich UI but
for validation lists also the XML. You can switch between both things by clicking on the
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tab on the lower part of the screen. For example in the Package Explorer select
"res/layout/main.xml".
5.3. Create attributes
Android allows you to create attributes for resources, e.g. for strings and / or colors.
These attributes can be used in your UI definition via XML or in your Java source code.
Select the file "res/values/string.xml" and press "Add". Select "Color" and enter
"myColor" as the name and "#3399CC" as the value.
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Add also the following "String" attributes. String attributes allow to translate the
application at a later point.
Table 1. String Attributes
Name ValuemyClickHandler myClickHandler
celsius to Celsius
fahrenheit to Fahrenheit
calc Calculate
Switch to the XML representation and validate the values.
Hello World, Convert!
Temperature Converter
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#3399CC
myClickHandler
to Celsius
to Fahrenheit
Calculate
5.4. Add UI Elements
Select "res/layout/main.xml" and open the Android editor via a double-click. This editor
allows you to create the UI via drag and drop or via the XML source code. You canswitch between both representations via the tabs at the bottom of the editor. For
changing the postion and grouping elements you can use the outline view.
The following shows a screenshot of the Palette view from which you can drag and drop
new UI elements into your layout. Please note that the "Palette" view changes frequently
so your view might be a bit different.
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Right-click on the text object Hello World, Hello! in the layout. Select Delete on the
popup menu to remove the text object. Then, from the Palette view, select Text Fields
and locate Plain Text. Drag this onto the layout to create a text input field. All object
types in the section "Text Fields derive from the class "EditText", they just specify via
an additional attribute which text type can be used.
Now select the Palette section Form Widgets and drag a RadioGroup object onto the
layout. The number of radio buttons added to the radio button group depends on your
version of Eclipse. Make sure there are two radio buttons by deleting or adding radio
buttons to the group.
From the Palette section Form Widgets, drag a Button object onto the layout.
The result should look like the following and the corresponding XML is listed below.
Make sure that your code is the same as listed below.
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Switch to "main.xml" and verify that your XML looks like the following.
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android:layout_width="wrap_content"
android:id="@+id/radio1"
android:layout_height="wrap_content">
5.5. Edit UI properties
If you select a UI element you can change its properties via the properties view. Most of
the properties can also be changed via the right mouse menu. Select the EditText field,
right mouse click on it, select Properties-> Text and delete the content. This means no
text will be initially shown in the text field.
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Assign the "celsius" string attribute to your "text" property of the first radio button and
"fahrenheit" to the second.
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From now on I assume you are able to use the properties menu on the UI elements. Set
the property "Checked" to true for the first RadioButton. Assign "calc" to the text
property of your button and assign "myClickHandler" to the "onClick" property. Set the
"Input type" property to "numberSigned" and "numberDecimal" on your EditText.
Right-click on the view in Graphical Layout mode, then select
Properties/Background... from the popup menu. Select Color and then myColor
in the list.
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Switch to the "main.xml" tab and verify that the XML is correctly maintained.
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android:id="@+id/radio1"
android:layout_height="wrap_content"
android:text="@string/fahrenheit">
5.6. Code your application
Change your code in "Convert.java" to the following. Note that the "myClickHandler"
will be called based on the "On Click" property of your button.
package de.vogella.android.temperature;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Toast;
publicclass Convert extends Activity {
private EditText text;
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@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
text = (EditText) findViewById(R.id.editText1);
}
// This method is called at button click because we assigned the name
to the
// "On Click property" of the button
publicvoid myClickHandler(View view) {
switch (view.getId()) {
case R.id.button1:
RadioButton celsiusButton = (RadioButton)
findViewById(R.id.radio0);
RadioButton fahrenheitButton = (RadioButton)
findViewById(R.id.radio1);
if (text.getText().length() == 0) {
Toast.makeText(this, "Please enter a valid
number",
Toast.LENGTH_LONG).show();
return;
}
float inputValue =
Float.parseFloat(text.getText().toString());
if (celsiusButton.isChecked()) {
text.setText(String
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.valueOf(convertFahrenheitToCelsius(inputValue)));
celsiusButton.setChecked(false);
fahrenheitButton.setChecked(true);
} else {
text.setText(String
.valueOf(convertCelsiusToFahrenheit(inputValue)));
fahrenheitButton.setChecked(false);
celsiusButton.setChecked(true);
}
break;
}
}
// Converts to celsius
privatefloat convertFahrenheitToCelsius(float fahrenheit) {
return ((fahrenheit - 32) * 5 / 9);
}
// Converts to fahrenheit
privatefloat convertCelsiusToFahrenheit(float celsius) {
return ((celsius * 9) / 5) + 32;
}
}
5.7. Start Project
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To start the Android Application, select your project, right click on it, Run-As-> Android
Application Be patient, the emulator starts up very slow. You should get the following
result.
Type in a number, select your conversion and press the button. The result should be
displayed and the other option should get selected.
5.8. Using the home menu
If you press the Home button you can also select your application.
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6. Menus
6.1. Menus
To use menusAndroidprovides two ways. First is the option menu which can be opened
via the menu button. The option menu of your activity is filled in the method
onCreateOptionsMenu() of your activity. You can register here a menu via your code or
use a XML menu resources which you inflate via a "MenuInflator". You get a
MenuInflator via your activity with the method getMenuInflator().
onCreateContextMenu() is only called once. If you want to influence the menu later you
have to use the method onPrepareOptionsMenu().
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The second option to display a menu is to use the context menu for a UI widget (view). A
context menu is activated if the user "long presses" the view.
A context menu for a view is registered via the method registerForContextMenu(view).
The method onCreateContextMenu() is called every time a context menu is activated asthe context menu is discarded after its usage. The Android platform may also add
options to your view, e.g. "EditText" provides context options to select text, etc.
6.2. Project
This chapter will demonstrate how to create and evaluate a option menu, how to define
preferences and how to navigate between activities via anintent . Create a project
"de.vogella.android.preferences" with the activity "HelloPreferences". Change the UI in
the file "/res/layout/main.xml" to the following:
6.3. Add a menu XML resource
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Menus can be defined via XML files. Select your project, right click on it and select New
-> Other -> Android -> "Android XML File". Select the option "Menu", enter as File
"menu.xml" and press the button "Finish".
Press Add and select "Item". Maintain the following value. This defines the entries in
your menu. We will have only one entry.
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Change your class "HelloPreferences" to the following. The OnCreateOptionsMenu
method is used to create the menu. The behavior in "onOptionsItemSelected" is
currently hard-coded to show a Toast and will soon call the preference settings. In case
you want to disable or hide menu items you can use the method
"onPrepareOptionsMenu" which is called every time the menu is called.
package de.vogella.android.preferences;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;
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publicclass HelloPreferences extends Activity {
/** Called when the activity is first created. */
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
publicboolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu, menu);
return true;
}
@Override
publicboolean onOptionsItemSelected(MenuItem item) {
Toast.makeText(this, "Just a test",
Toast.LENGTH_SHORT).show();
return true;
}
}
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Run your application and press "Menu" on the emulator. Your menu should be
displayed. If you select the menu entry you should see a small info message.
The two "Preference" buttons are not yet active. We will use them in the next chapter.
7. Preferences and Intents
7.1. Overview
Preferences allow you to save data for your application. Preferences are stored as key
values.Intentsallow you to start Activities from other Activities.
7.2. Using preferences
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We will continue using the example project "de.vogella.android.preferences" from the
last chapter.
Preference values can also be stored as a XML resource. Create another Android XML
File "preferences.xml" this time of type "Preference".
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Press Add, add a category and add two preferences "EditTextPreferences" to this
category : "User" and "Password".
To allow the user to enter the preference value you can define a Activity with extends
PreferenceActivity. This activity can load a preference definition resources via the
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method addPreferencesFromResource(). Create the class "Preferences" which will load
the "preference.xml".
package de.vogella.android.preferences;
import android.os.Bundle;
import android.preference.PreferenceActivity;
publicclass Preferences extends PreferenceActivity {
/** Called when the activity is first created. */
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}
}
To make this class available as an activity for Android you need to register it in your
"AndroidManifest.xml" file. Select "AndroidManifest.xml" and the tab "Application".
Add the activity "Preferences".
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The first button will show the current values of the preferences via a Toast and the
second button will revert the maintained user name to demonstrate how you couldchange the preferences via code.
package de.vogella.android.preferences;
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import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
publicclass HelloPreferences extends Activity {
SharedPreferences preferences;
/** Called when the activity is first created. */
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button button = (Button) findViewById(R.id.Button01);
// Initialize preferences
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preferences =PreferenceManager.getDefaultSharedPreferences(this);
button.setOnClickListener(new OnClickListener() {
publicvoid onClick(View v) {
String username =
preferences.getString("username", "n/a");
String password =
preferences.getString("password", "n/a");
Toast.makeText(
HelloPreferences.this,
"You entered user: " + username+ " and password: "
+ password,
Toast.LENGTH_LONG).show();
}
});
Button buttonChangePreferences = (Button)
findViewById(R.id.Button02);
buttonChangePreferences.setOnClickListener(new
OnClickListener() {
publicvoid onClick(View v) {
Editor edit = preferences.edit();
String username =
preferences.getString("username", "n/a");
// We will just revert the current user name
and save again
StringBuffer buffer = new StringBuffer();
for (int i = username.length() - 1; i >= 0; i--
) {
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buffer.append(username.charAt(i));
}
edit.putString("username", buffer.toString());
edit.commit();
// A toast is a view containing a quick little
message for the
// user. We give a little feedback
Toast.makeText(HelloPreferences.this,
"Reverted string sequence of
user name.",
Toast.LENGTH_LONG).show();
}
});
}
}
We will update the method onOptionsItemSelected() to open the activity "Preferences"
once you select the option menu. Even though we currently have only one option in our
menu we use a switch to be ready for several new menu entries. To see the current
values of the preferences we define a button and use the class "PreferenceManager" to
get the sharedPreferences.
@Override
publicboolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu, menu);
return true;
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}
// This method is called once the menu is selected
@Override
publicboolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
// We have only one menu option
case R.id.preferences:
// Launch Preference activity
Intent i = new Intent(HelloPreferences.this,
Preferences.class);
startActivity(i);
// Some feedback to the user
Toast.makeText(HelloPreferences.this,
"Here you can enter your user
credentials.",
Toast.LENGTH_LONG).show();
break;
}
return true;
}
7.3. Run
Run your application. Press the "menu" hardware button and then select your menu
item "Preferences". You should be able to enter your user settings then press the back
hardware button to return to your main activity. The saved values should be displayed in
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a small message windows (Toast) if you press your first button. If you press the second
button the username should be reversed.
8. Dialogs via the AlertDialog
We have already used a "Toast" which is a small message window which does not take
the focus. In this chapter we will use the class "AlertDialog". AlertDialog is used to open
a dialog from our activity. This modal dialog gets the focus until the user closes it.
An instance of this class can be created by the builder pattern, e.g. you can chain your
method calls.
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You should always open a dialog from the class onCreateDialog(int) as the Android
system manages the dialog in this case for you. This method is automatically called by
Android if you call showDialog(int).
Create a new Android project "de.vogella.android.alertdialog" with the activity"ShowMyDialog". Maintain the following layout for "main.xml".
Change the code of your activity to the following.
package de.vogella.android.alertdialog;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.app.Dialog;
import android.content.DialogInterface;
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import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
publicclass ShowMyDialog extends Activity {
/** Called when the activity is first created. */
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
publicvoid openMyDialog(View view) {
showDialog(10);
}
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case 10:
// Create out AlterDialog
Builder builder = new AlertDialog.Builder(this);
builder.setMessage("This will end the activity");
builder.setCancelable(true);
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builder.setPositiveButton("I agree", new
DialogInterface.OnClickListener() {
publicvoid onClick(DialogInterface dialog, int which) {
ShowMyDialog.this.finish();
}
});
builder.setNegativeButton("No, no", new
DialogInterface.OnClickListener() {
publicvoid onClick(DialogInterface dialog, int which) {
Toast.makeText(getApplicationContext(),"Activity will
continue",Toast.LENGTH_LONG).show();
}
});
AlertDialog dialog = builder.create();
dialog.show();
}
returnsuper.onCreateDialog(id);
}
}
If you run your application and click your button you should see your dialog.
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More on dialogs can be found onAndroid Dialogs standard documentation.
9. TableLayout
9.1. Overview
In earlier chapter we have used the LinearLayout which allows you to stack widgets
vertical or horizontal. LinearLayout can be nested to achieve nice effects. This chapter
will demonstrate the usage of "TableLayout".
This layout allows you to organize a view into a table format. You specify via the view
group "TableRow" rows for your table. Afterwards you put widgets into the individual
rows.
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On the "TableLayout" you can define which column should take additional space via the
"android:stretchColumns" attribute. If several columns should take the available space
you can specify them as a comma-separated list. Similar you can use the attribute
"android:shrinkColumn", which will try to word-wrap the content of the specified
widgets and the attribute "android:collapseColums" to define initially hidden columns.
Via Java you can display / hide these columns via the method setColumnVisible().
Columns will be automatically created based on the maximum number of widgets in one
row. Per default each widgets creates a new column in the row. You can specific via
"android:layout_column" the column a widget should go and via "android:layout_span"
how many columns a widget should take.
You can also put non TableRows in a table. This way you can for example add dividers
between your columns.
9.2. Example
Create the project "de.vogella.android.layout.table" with the activity
"DemoTableLayout". Change "main.xml" to the following.
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android:layout_width="wrap_content"
android:layout_height="wrap_content">
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Change the activity "DemoTableLayout" to the following to use the button to hide the
second column in the table.
package de.vogella.android.layout.table;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
importandroid.widget.Button;
import android.widget.TableLayout;
publicclass DemoTableLayout extends Activity {
private TableLayout layout;
private Button button;
/** Called when the activity is first created. */
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
layout = (TableLayout) findViewById(R.id.tableLayout1);
button = (Button) findViewById(R.id.collapse);
}
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publicvoid toogleHiddenRows(View view) {
// Second row has index 1
layout.setColumnCollapsed(1, !layout.isColumnCollapsed(1));
if (layout.isColumnCollapsed(1)) {
button.setText("Show second column");
} else {
button.setText("Hide second column");
}
}
}
10. ContentProvider
10.1. Overview
ContentProvider are used to provide data from an application to another.ContentProvider do not store the data but provide the interface for other applications to
access the data.
The following example will use an existing context provider from "Contacts".
10.2. Create contacts on your emulator
For this example we need a few maintained contacts. Select the home menu and then
the menu entry "Contacts" to create contacts.
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Press Menu and select "New Contact".
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As a result you should have a few new contacts.
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10.3. Using the Contact Content Provider
Create a new Android project "de.vogella.android.contentprovider" with the activity
"ContactsView".
Rename the id of the existing TextView from the example wizard to "contactview".
Delete the default text. Also change the layout_height to "fill_parent".
The resulting main.xml should look like the following.
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android:layout_height="fill_parent">
Access to the contact content provider require a certain permission as not all
applications should have access to the contact information. Open the
AndroidManifest.xml, and select the Permissions tab. On that tab click the "Add" button,
and select "Uses Permission". From the drop-down list select the entry
"android.permission.READ_CONTACTS".
Change the coding of the activity.
package de.vogella.android.contentprovider;
import android.app.Activity;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.widget.TextView;
publicclass ContactsView extends Activity {
/** Called when the activity is first created. */
@Override
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publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TextView contactView = (TextView)findViewById(R.id.contactview);
Cursor cursor = getContacts();
while (cursor.moveToNext()) {
String displayName = cursor.getString(cursor
.getColumnIndex(ContactsContract.Data.DISPLAY_NAME));
contactView.append("Name: ");
contactView.append(displayName);
contactView.append("\n");
}
}
private Cursor getContacts() {
// Run query
Uri uri = ContactsContract.Contacts.CONTENT_URI;
String[] projection = new String[]
{ ContactsContract.Contacts._ID,
ContactsContract.Contacts.DISPLAY_NAME };
String selection = ContactsContract.Contacts.IN_VISIBLE_GROUP
+ " = '"
+ ("1") + "'";
String[] selectionArgs = null;
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String sortOrder = ContactsContract.Contacts.DISPLAY_NAME
+ " COLLATE LOCALIZED ASC";
return managedQuery(uri, projection, selection, selectionArgs,
sortOrder);
}
}
Typically you would display such data in aListView. Please see theListView Tutorialfordetails.
11. ScrollView
ScrollViews can be used to contain one view that might be to big to fit on one screen. If
the view is to big the ScrollView will display a scroll bar to scroll the context. Of course
this view can be a layout which can then contain other elements.
Create an android project "de.vogella.android.scrollview" with the activity "ScrollView".
Create the following layout and class.
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android:text="This is a header"
android:textAppearance="?android:attr/textAppearanceLarge"
android:paddingLeft="8dip" android:paddingRight="8dip"
android:paddingTop="8dip">
package de.vogella.android.scrollview;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
importandroid.widget.TextView;
publicclass ScrollView extends Activity {
/** Called when the activity is first created. */
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@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TextView view = (TextView) findViewById(R.id.TextView02);
String s="";
for (int i=0; i < 100; i++) {
s += "vogella.de ";
}
view.setText(s);
}
}
The attribute "android:fillViewport="true"" ensures that the the scrollview is set to the
full screen even if the elements are smaller then one screen and the "layout_weight" tell
the android system that these elements should be extended.
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12. DDMS perspective and important views
12.1. DDMS - Dalvik Debug Monitor Server
Eclipse provides aperspectivefor interacting with your device and program.Open it to
see the possible options. This perspective includes the following views which can also be
used independently and allows to place calls and send SMS to the device. It also allow to
set the current geo position and toperform a performance traceof your application.
12.2. LogCat View
You can see the log (including System.out.print() statements) via the LogCat view.
http://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/AndroidPerformance/article.html#traceviewhttp://www.vogella.de/articles/AndroidPerformance/article.html#traceviewhttp://www.vogella.de/articles/AndroidPerformance/article.html#traceviewhttp://www.vogella.de/articles/AndroidPerformance/article.html#traceviewhttp://www.vogella.de/articles/Eclipse/article.html#perspectivehttp://www.vogella.de/articles/Eclipse/article.html#perspective8/3/2019 How to Develop Android Apps
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12.3. File explorer
The file explorer allows to see the files on the android simulator.
13. Shell
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13.1. Android Debugging Bridge - Shell
You can access your Android emulator also via the console. Open a shell, switch to your
"android-sdk" installation directory into the folder "tools". Start the shell via the
following command "adb shell".
adb shell
You can also copy file from and to your device via the following commands.
// Assume the gesture file exists on your Android device
adb pull /sdcard/gestures ~/test
// Now copy it back
adb push ~/test/gesture /sdcard/gestures2
This will connect you to your device and give youLinux command line access to the
underlying file system, e.g. ls, rm, mkdir, etc. The application data is stored in the
directory "/data/data/package_of_your_app".
If you have several devices running you can issue commands to one individuel device.
# Lists all devices
adb devices
#Result
List of devices attached
emulator-5554 attached
emulator-5555 attached
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# Issue a command to a specific device
adb -s emulator-5554 shell
13.2. Uninstall an application via adb
You can uninstall an android application via the shell. Switch the the data/app directory
(cd /data/app) and simply delete your android application.
13.3. Emulator Console via telnet
Alternatively to adb you can also use telnet to connect to the device. This allows you to
simulate certain things, e.g. incoming call, change the network "stability", set your
current geocodes, etc. Use "telnet localhost 5554" to conntect to your simulated device.
To exit the console session, use the command "quit" or "exit".
For example to change the power settings of your phone, to receive an sms and to get an
incoming call make the following.
# connects to device
telnet localhost 5554
# set the power level
power status full
power status charging
# make a call to the device
gsm call 012041293123
# send a sms to the device
sms send 12345 Will be home soon
# set the geo location
geo fix 48 51
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For more information on the emulator console please seeEmulator Console manual
14. Deploy your application on a real device
Turn on "USB Debugging" on your device in the settings. Select in the settings
Applications > Development, then enable USB debugging. You also need to install the
driver for your mobile phone. For details please seeDeveloping on a Device . Please note
that the Android version you are developing for must be the installed version on your
phone.
To select your phone, select the "Run Configurations", select "Manual" selection and
select your device.
15. Thank you
Please help me to support this article:
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16. Questions and Discussion
Before posting questions, please see thevogella FAQ. If you have questions or find an
error in this article please use thewww.vogella.de Google Group. I have created a short
listhow to create good questionswhich might also help you.
17. Links and Literature
17.1. Source Code
Source Code of Examples
17.2. Android Resources
Android 2 (German Book)
Android ListView and ListActivity
Android Location API and Google Maps
Android Intents
Android and Networking
Android Homepage
Android Developer Homepage
Android Issues / Bugs
Android Google Groups
http://www.vogella.de/faq.htmlhttp://www.vogella.de/faq.htmlhttp://www.vogella.de/faq.htmlhttp://groups.google.com/group/vogellahttp://groups.google.com/group/vogellahttp://groups.google.com/group/vogellahttp://www.vogella.de/blog/2010/03/09/asking-community-questions/http://www.vogella.de/blog/2010/03/09/asking-community-questions/http://www.vogella.de/code.htmlhttp://www.vogella.de/code.htmlhttp://dpunkt.de/s/androidhttp://dpunkt.de/s/androidhttp://www.vogella.de/articles/AndroidListView/article.htmlhttp://www.vogella.de/articles/AndroidListView/article.htmlhttp://www.vogella.de/articles/AndroidLocationAPI/article.htmlhttp://www.vogella.de/articles/AndroidLocationAPI/article.htmlhttp://www.vogella.de/articles/AndroidIntent/article.htmlhttp://www.vogella.de/articles/AndroidIntent/article.htmlhttp://www.vogella.de/articles/AndroidNetworking/article.htmlhttp://www.vogella.de/articles/AndroidNetworking/article.htmlhttp://code.google.com/intl/de-DE/android/http://code.google.com/intl/de-DE/android/http://developer.android.com/http://developer.android.com/http://code.google.com/p/android/issues/listhttp://code.google.com/p/android/issues/listhttp://groups.google.com/group/android-developershttp://groups.google.com/group/android-developershttp://flattr.com/thing/49772/Tutorials-for-Eclipse-Java-Android-and-Webprogramminghttp://flattr.com/thing/49772/Tutorials-for-Eclipse-Java-Android-and-Webprogramminghttp://groups.google.com/group/android-developershttp://code.google.com/p/android/issues/listhttp://developer.android.com/http://code.google.com/intl/de-DE/android/http://www.vogella.de/articles/AndroidNetworking/article.htmlhttp://www.vogella.de/articles/AndroidIntent/article.htmlhttp://www.vogella.de/articles/AndroidLocationAPI/article.htmlhttp://www.vogella.de/articles/AndroidListView/article.htmlhttp://dpunkt.de/s/androidhttp://www.vogella.de/code.htmlhttp://www.vogella.de/blog/2010/03/09/asking-community-questions/http://groups.google.com/group/vogellahttp://www.vogella.de/faq.html8/3/2019 How to Develop Android Apps
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Android Assets Studio
17.3. vogella Resources
Eclipse RCP Training (German) Eclipse RCP Training with Lars Vogel
Android Tutorial Introduction to Android Programming
GWT Tutorial Program in Java and compile to JavaScript and HTML
Eclipse RCP Tutorial Create native applications in Java
JUnit Tutorial Test your application
Git Tutorial Put everything you have under distributed version control system
http://android-ui-utils.googlecode.com/hg/asset-studio/dist/index.htmlhttp://android-ui-utils.googlecode.com/hg/asset-studio/dist/index.htmlhttp://www.vogella.de/training/eclipsercp.htmlhttp://www.vogella.de/training/eclipsercp.htmlhttp://www.vogella.de/articles/Android/article.htmlhttp://www.vogella.de/articles/Android/article.htmlhttp://www.vogella.de/articles/GWT/article.htmlhttp://www.vogella.de/articles/EclipseRCP/article.htmlhttp://www.vogella.de/articles/JUnit/article.htmlhttp://www.vogella.de/articles/Git/article.htmlhttp://www.vogella.de/articles/Git/article.htmlhttp://www.vogella.de/articles/JUnit/article.htmlhttp://www.vogella.de/articles/EclipseRCP/article.htmlhttp://www.vogella.de/articles/GWT/article.htmlhttp://www.vogella.de/articles/Android/article.htmlhttp://www.vogella.de/training/eclipsercp.htmlhttp://android-ui-utils.googlecode.com/hg/asset-studio/dist/index.html