C# Starter L03-Utilities

Mohammad Shakermohammadshaker.com

C# Programming Course@ZGTRShaker

2011, 2012, 2013, 2014

C# StarterL03 – Utilities

Today’s Agenda

• const and readonly

• Casting– Direct Casting

– as Keyword

• is Keyword

• enums

• Exception Handling

• UnSafe Code

• Nullable Types

• using Keyword

• Files

• Class Diagram

• Windows Forms

const and readonly

const and readonly

• const

– Must be initialized in the time of declaration

• readonly

– keyword is a modifier that you can use on fields. When a field declaration includes

a readonly modifier, assignments to the fields introduced by the declaration can only occur as

part of the declaration or in a constructor in the same class.

public const int WEIGHT = 1000;

public readonly int y = 5;

const and readonly

• const


• readonly







public readonly int y;

const and readonly

• const


• readonly







public readonly int y;

Casting

Casting

Direct Casting “as” Keyword

void Example(object o){

// Castingstring s = (string)o; // 1 (Direct Casting)// -OR-string s = o as string; // 2 (Casting with “as” Keyword)// -OR-string s = o.ToString(); // 3 Calling a method

}

Casting

• What’s the difference? Output?



}

Casting


Number (“1”)• If (o is not a string) Throws InvalidCastException if o is not a string. • Otherwise, assigns o to s, even if o is null.



}

Casting


Number (“2”)• Assigns null to s if o is not a string or if o is null. • Otherwise assign to s “CAN’T BE A NULL VALUE”For this reason, you cannot use it with value types.



}

Casting


Number(“3”)• Causes a NullReferenceException of o is null.• Assigns whatever o.ToString() returns to s, no matter what type o is.



}

Casting


1. Throws InvalidCastException if o is not a string. Otherwise, assigns o to s, even if o is null.2. Assigns null to s if o is not a string or if o is null. Otherwise, assigns o to s. For this reason, you cannot use it with

value types.3. Causes a NullReferenceException of o is null. Assigns whatever o.ToString() returns to s, no matter what type o is.


// I swear o is a string, C# compiler! I’m ordering you to cast, I know what am doing!string s = (string)o; // 1 (Direct Casting)// I Donna know whether o is a string or not, try a cast and tell me!string s = o as string; // 2 (Casting with “as” Keyword)// Am programming badly with this code!string s = o.ToString(); // 3 Calling a method

}

Casting

• Meaning!



}

Casting

• Meaning!

“as” casting will never throw an exception, while “Direct cast” can.



}

Casting

• Meaning!

“as” casting will never throw an exception, while “Direct cast” can.

“as” cannot be used with value types (non-nullable types).

using System;class MyClass1{}

class MyClass2{}

public class IsTest{

public static void Main(){

object[] myObjects = new object[6];myObjects[0] = new MyClass1();myObjects[1] = new MyClass2();myObjects[2] = "hello";myObjects[3] = 123;myObjects[4] = 123.4;myObjects[5] = null;

for (int i = 0; i < myObjects.Length; ++i){

string s = myObjects[i] as string;Console.Write("{0}:", i);if (s!= null)

Console.WriteLine("'" + s + "'");else

Console.WriteLine("not a string");}

}}

Casting

using System;class MyClass1{}

class MyClass2{}

public class IsTest{


object[] myObjects = new object[6];myObjects[0] = new MyClass1();myObjects[1] = new MyClass2();myObjects[2] = "hello";myObjects[3] = 123;myObjects[4] = 123.4;myObjects[5] = null;

for (int i = 0; i < myObjects.Length; ++i){

string s = myObjects[i] as string;Console.Write("{0}:", i);if (s!= null)

Console.WriteLine("'" + s + "'");else

Console.WriteLine("not a string");}

}}

Casting

0:not a string1:not a string2:'hello'3:not a string4:not a string5:not a string

is Keyword

“is” Keyword

• The is operator is used to check whether the run-time type of an object is

compatible with a given type.

• The is operator is used in an expression of the form:

expression is type

“is” Keyword

• Let’s have the following example

class Class1{}class Class2{}

“is” Keywordpublic class IsTest{

public static void Test(object o){

Class1 a;Class2 b;if (o is Class1){

Console.WriteLine("o is Class1");a = (Class1)o;// do something with a

}else if (o is Class2){

Console.WriteLine("o is Class2");b = (Class2)o;// do something with b

}else{

Console.WriteLine("o is neither Class1 nor Class2.");}

}public static void Main(){

Class1 c1 = new Class1();Class2 c2 = new Class2();Test(c1);Test(c2);Test("a string");

}}

“is” Keywordpublic class IsTest{

public static void Test(object o){

Class1 a;Class2 b;if (o is Class1){

Console.WriteLine("o is Class1");a = (Class1)o;// do something with a

}else if (o is Class2){

Console.WriteLine("o is Class2");b = (Class2)o;// do something with b

}else{

Console.WriteLine("o is neither Class1 nor Class2.");}

}public static void Main(){

Class1 c1 = new Class1();Class2 c2 = new Class2();Test(c1);Test(c2);Test("a string");

}}

o is Class1o is Class2o is neither Class1 nor Class2.Press any key to continue...

enum

enum

• As easy as:

• And that’s it!

// You define enumerations outside of other classes.public enum DaysOfWeek { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };

DaysOfWeek dayOfWeek = DaysOfWeek.Monday;

if(dayOfWeek == Wednesday){

// Do something here}

Exception Handling

Exception Hierarchy

Exception Handling

using System;using System.IO;

class tryCatchDemo{

static void Main(string[] args){

try{

File.OpenRead("NonExistentFile");}catch(Exception ex){

Console.WriteLine(ex.ToString());}

}}

The output?

Exception Handling


class tryCatchDemo{


try{



}}

The output?

Exception Handling


class tryCatchDemo{


try{



}}

The output?

Exception Handling – Multiple “catch”s

try{

int number = Convert.ToInt32(userInput);}catch (FormatException e){

Console.WriteLine("You must enter a number.");}catch (OverflowException e){

Console.WriteLine("Enter a smaller number.");}catch (Exception e){

Console.WriteLine("An unknown error occurred.");}

Exception Handling

• Multiple catch statement?!

catch(FileNotFoundException e){

Console.WriteLine(e.ToString());}catch(Exception ex){


Exception Handling – finally keywordclass FinallyDemo{


FileStream outStream = null;FileStream inStream = null;

try{

outStream = File.OpenWrite("DestinationFile.txt");inStream = File.OpenRead("BogusInputFile.txt");

}catch(Exception ex){

Console.WriteLine(ex.ToString());}finally{

if (outStream!= null){

outStream.Close();Console.WriteLine("outStream closed.");

}if (inStream!= null){

inStream.Close();Console.WriteLine("inStream closed.");

}}

}}

Throwing Exceptions

Throwing Exceptions

• Like this:

• But why?

public void CauseProblemsForTheWorld() //always up to no good...{

throw new Exception("Just doing my job!");}

Searching for a catch

• Caller chain is traversed backwards until a method with a matching catch clause is

found.

• If none is found => Program is aborted with a stack trace

• Exceptions don't have to be caught in C# (in contrast to Java)

Creating Exceptions

Creating Exceptions

• Let’s throw an exception when you over-eat Hamburgers!

• Now you can say:

public class AteTooManyHamburgersException : Exception {

public int HamburgersEaten { get; set; }

public AteTooManyHamburgersException(int hamburgersEaten){

HamburgersEaten = hamburgersEaten;}

}

try{

EatSomeHamburgers(32);}catch(AteTooManyHamburgersException hamburgerException){

Console.WriteLine(hamburgerException.HamburgersEaten + " is too many hamburgers.");}

Unsafe Code!

Unsafe Code!

• unsafe code == (code using explicit pointers and memory allocation) in C#

// The following fixed statement pins the location of// the src and dst objects in memory so that they will// not be moved by garbage collection. fixed (byte* pSrc = src, pDst = dst){

byte* ps = pSrc;byte* pd = pDst;

// Loop over the count in blocks of 4 bytes, copying an// integer (4 bytes) at a time:for (int n =0; n < count/4; n++){

*((int*)pd) = *((int*)ps);pd += 4;ps += 4;

}

Nullable Types

Nullable Types - The Concept

Nullable Types

• Declaration

DateTime? startDate;

Nullable Types

• Declaration


// You can assign a normal value to startDate like this:startDate = DateTime.Now;

Nullable Types

• Declaration


// You can assign a normal value to startDate like this:startDate = DateTime.Now;

// or you can assign null, like this:startDate = null;

Nullable Types

• Declaration

// Here's another example that declares and initializes a nullable int:int? unitsInStock = 5;

Nullable Types

class Program{

static void Main(){

DateTime? startDate = DateTime.Now;bool isNull = startDate == null;Console.WriteLine("isNull: " + isNull);

}}

Nullable Types

class Program{

static void Main(){

DateTime? startDate = DateTime.Now;bool isNull = startDate == null;Console.WriteLine("isNull: " + isNull);

}}

isNull: FalsePress any key to continue...

Nullable Types

class Program{

static void Main(){

int i = null;}

}

Nullable Types

class Program{

static void Main(){

int i = null;}

}

Compiler error, Can’t convert from null to type int

using keywordusing Directive - using statement

using Directive

using Directive

• The using Directive has two uses:

– To permit the use of types in a namespace so you do not have to qualify the use of a type in

that namespace:

– To create an alias for a namespace or a type:

using System.Text;

using Project = PC.MyCompany.Project;

using Directive

namespace PC{

// Define an alias for the nested namespace.using Project = PC.MyCompany.Project;class A{

void M(){

// Use the aliasProject.MyClass mc = new Project.MyClass();

}}namespace MyCompany{

namespace Project{

public class MyClass { }}

}}

using Directive

namespace PC{


void M(){



namespace Project{


}}

using Directive

namespace PC{


void M(){



namespace Project{


}}

using Directive

namespace PC{


void M(){



namespace Project{


}}

using statement

using statement

• C#, through the.NET Framework common language runtime (CLR), automatically

releases the memory used to store objects that are no longer required.

• The release of memory is non-deterministic; memory is released whenever the

CLR decides to perform garbage collection. However, it is usually best to release

limited resources such as file handles and network connections as quickly as

possible.

using Directive

• Defines a scope, outside of which an object or objects will be disposed.

using (Font font1 = new Font("Arial", 10.0f)) {

// Use font1}

using Directive

• Defines a scope, outside of which an object or objects will be disposed.

using (Font font1 = new Font("Arial", 10.0f)) {

// Use font1}

using (Font font3 = new Font("Arial", 10.0f), font4 = new Font("Arial", 10.0f)) {

// Use font3 and font4. }

using Directiveclass C : IDisposable{

public void UseLimitedResource(){

Console.WriteLine("Using limited resource...");}

void IDisposable.Dispose(){

Console.WriteLine("Disposing limited resource.");}

}

class Program{

static void Main(){

using (C c = new C()){

c.UseLimitedResource();}Console.WriteLine("Now outside using statement.");Console.ReadLine();

}}






}

class Program{

static void Main(){



}}






}

class Program{

static void Main(){



}}






}

class Program{

static void Main(){



}}






}

class Program{

static void Main(){



}}






}

class Program{

static void Main(){



}}






}

class Program{

static void Main(){



}}

Using limited resource...Disposing limited resource.Now outside using statement.

Type Aliases

Type Aliases

• For instant naming we can use this for long type names:

• And then just using it as follow

using SB = System.Text.StringBuilder;

SB stringBuilder = new SB("InitialValue");

Files

Files, One Shot Reading

// Change the file path here to where you want it.String path = @”C:/Users/Mhd/Desktop/test1.txt”;

string fileContents = File.ReadAllText(path);

string[] fileContentsByLine = File.ReadAllLines(path);

Files, One Shot Writing


string informationToWrite = "Hello world!";File.WriteAllText(path, informationToWrite);

string[] arrayOfInformation = new string[2];arrayOfInformation[0] = "This is line 1";arrayOfInformation[1] = "This is line 2";File.WriteAllLines(path, arrayOfInformation);

FilesReading and Writing on a Text-based Files

Files

• StreamWriter

– Object for writing a stream down

• StreamReader

– Object for reading a stream up


public partial class Test{


string path = @"c:\temp\MyTest.txt";

// Create a file to write to.using (StreamWriter sw = new StreamWriter(path)){

sw.WriteLine("Hello");sw.WriteLine("And");sw.WriteLine("Welcome");

}

// Open the file to read from.using (StreamReader sr = new StreamReader(path)){

string s = "";while ((s = sr.ReadLine())!= null){

Console.WriteLine(s);}

}}

}







}




}}

}

HelloAndWelcomePress any key to continue...







}




}}

}

HelloAndWelcomePress any key to continue...


class Test{


string path = @"c:\temp\MyTest.txt";if (!File.Exists(path)){

// Create a file to write to.using (StreamWriter sw = File.CreateText(path)){


}}

// Open the file to read from.using (StreamReader sr = File.OpenText(path)){



}}

}


class Test{





}}




}}

}


class Test{





}}




}}

}


class Test{





}}




}}

}


class Test{





}}

// Open the file to read from.

using (StreamReader sr = File.OpenText(path)){



}}

}

Reading and Writing on a Binary FilesBinaryWriter and BinaryReader


FileStream fileStream = File.OpenWrite(path);BinaryWriter binaryWriter = new BinaryWriter(fileStream);

binaryWriter.Write(2);binaryWriter.Write("Hello");

binaryWriter.Flush();binaryWriter.Close();

Class Diagram

Class Diagram

Windows Forms

Windows Forms

To learn more about Windows Forms,visit my C++.NET course @

http://www.slideshare.net/ZGTRZGTR/exactly the same as C#

http://www.slideshare.net/ZGTRZGTR/

That’s it for today!

C# Starter L03-Utilities

Technology

casting string s

type o

nullreferenceexception

string console

void exampleobject o

casting whats

casting meaning

public readonly int