Using Java interop in your Xamarin.Andr oid apps @WMeints
Mar 23, 2016
Using Java interop in your
Xamarin.Android apps
@WMeints
AgendaJava interop… wait what!?Beyond basic interopBuilding your own interop components
JAVA INTEROP, WAIT WHAT?!
Java interop, what what?!Building an Android app in C#
namespace TaskTracker.Client.Android{ [Activity(Label = "TaskTracker.Client.Android", MainLauncher = true, Icon = "@drawable/icon")] public class Activity1 : ListActivity { private TasksOfflineContext _context;
protected override void OnCreate(Bundle bundle) { base.OnCreate(bundle);
_context = new TasksOfflineContext("sync", new Uri("http://10.0.2.2:15314/taskssyncservice.svc/"));
_context.CacheController.ControllerBehavior.SerializationFormat = SerializationFormat.ODataJSON;
_context.CacheController.RefreshCompleted += OnRefreshCompleted; _context.CacheController.RefreshAsync(); }
Java interop, what what?!Meanwhile in Java country…
Cross Platform Mobile Development - Android
public class Activity1 extends android.app.ListActivity implements mono.android.IGCUserPeer{
static final String __md_methods;static {
__md_methods = "n_onCreate:(Landroid/os/Bundle;)V:GetOnCreate_Landroid_os_Bundle_Handler\n" +"";
mono.android.Runtime.register ("TaskTracker.Client.Android.Activity1, “ + “TaskTracker.Client.Android, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=null", Activity1.class, __md_methods);
}
public Activity1 (){
super ();if (getClass () == Activity1.class)
mono.android.TypeManager.Activate ("TaskTracker.Client.Android.Activity1, “ + “TaskTracker.Client.Android, Version=1.0.0.0,
Culture=neutral, “ …
Java interop, what what?!
Linux Kernel
Mono (.NET Runtime) Dalvik (Java Runtime)
.NET APIs Android Bindings
Android.* Java.*MCW
ACW
Android callable wrappers
Mono callable wrappers
Java interop, wait what?!What you are essentially doing is building apps that rely heavily upon interop.
In fact: Everything you build on Android will at some point talk to a piece Java code.
Cross Platform Mobile Development - Android
Java interop, wait what?!So why not take advantage of the situation?
– You can extend your app with Java code– Found a cool Android library? Bind it!
Cross Platform Mobile Development - Android
BEYOND BASIC INTEROP
Beyond basic interopThe two-way traffic between Android and Mono is done through two endpoints:
– Mono Java Mono Callable Wrappers– Java Mono Android Callable Wrappers
Cross Platform Mobile Development - Android
Beyond basic interop - MCWs
Linux Kernel
Mono (.NET Runtime) Dalvik (Java Runtime)
.NET APIs Android Bindings
Android.* Java.*MCW
ACW
Beyond basic interop – MCWsTalking to Java from .NET is done through the Java Native Interface
– The next bit is going to get pointy or pointerific depending on what you like…
Cross Platform Mobile Development - Android
MCW INTERNALSDemo
Cross Platform Mobile Development - Android
Beyond basic interop – MCWsSteps to create an instance of a Java class– Find the handle to the type– Marshal constructor arguments– Invoke the constructor– Safe the instance pointer!
Cross Platform Mobile Development - Android
Beyond basic interop – MCWsSteps to invoke a Java method:– Find the handle to the method– Marshal the arguments– Invoke the method
Cross Platform Mobile Development - Android
Beyond basic interop – MCWsNotice the TransferOwnership settings
– Important, who is the owner of the handle?– Care must be taken when transferring handles– If two objects own a handle, the app will be
unstable!
Cross Platform Mobile Development - Android
Beyond basic interop – MCWsImportant to know:
– When invoking JNI, native handles are used– Has effect on garbage collection, so clean it up!– Please, Reduce the amount of memory copy
actions, it will improve the performance.
Cross Platform Mobile Development - Android
Beyond basic interop - ACWs
Linux Kernel
Mono (.NET Runtime) Dalvik (Java Runtime)
.NET APIs Android Bindings
Android.* Java.*MCW
ACW
ACW INTERNALSDemo
Cross Platform Mobile Development - Android
Beyond basic interop - ACWsAndroid callable wrappers are the least of your problems.
– Generated by the Mono compiler– Don’t touch or you will break them!
Cross Platform Mobile Development - Android
Performance considerationsA few things you need to know:
– Value types are copied between Java and Mono– For reference types pointers are exchanged– 4 bytes in .NET != 4 bytes in Java, sometimes
Cross Platform Mobile Development - Android
Beware Bitmap users!
BUILDING YOUR OWN INTEROP
Building your own interopExplicit use of interop is possible from your own app through these methods:
– Add Java source files to your project– Create bindings for an existing library
Cross Platform Mobile Development - Android
Adding Java sourcesAdd a .java file to your project for
– You found an activity or service that you don’t want to translate to .NET code
– You have a single component, but not enough to create a library (Please keep it to one file).
Cross Platform Mobile Development - Android
ADDING JAVA SOURCESDemo
Cross Platform Mobile Development - Android
Binding Java librariesThis is the real stuff, the big one, the goodest.
– Allows you to use existing libraries– Automatically generates wrappers for Java classes
based on the settings you provide.
Cross Platform Mobile Development - Android
Binding Java librariesThe steps for binding a Java library:
1. Add the Java library to the binding project2. Customize the transformations 3. Extend the library with your own goodies
Cross Platform Mobile Development - Android
Binding Java librariesThe steps for binding a Java library:
1. Add the Java library to the binding project2. Customize the transformations 3. Extend the library with your own goodies
Cross Platform Mobile Development - Android
BINDING A JAVA LIBRARYDemo
Cross Platform Mobile Development - Android
Binding Java librariesThe steps for binding a Java library:
1. Add the Java library to the binding project2. Customize the transformations 3. Extend the library with your own goodies
Cross Platform Mobile Development - Android
CUSTOMIZING TRANSFORMATIONSDemo
Cross Platform Mobile Development - Android
Binding Java librariesThe steps for binding a Java library:
1. Add the Java library to the binding project2. Customize the transformations 3. Extend the library with your own goodies
Cross Platform Mobile Development - Android
EXTENDING BINDINGSDemo
Cross Platform Mobile Development - Android
Final thoughtsJava interop is all around you in Xamarin.Android
– Don’t worry too much about it in your day-to-day Android development.
– Use it when you need it, to get more power!
Cross Platform Mobile Development - Android