cwpfl03-utilityp1-140211141153-phpapp02

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Mohammad Shaker

mohammadshaker.com

C# Programming Course

@ZGTRShaker

2011, 2012, 2013, 2014

C# StarterL03 Utilities


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const and readonly


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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 inclua readonly modifier, assignments to the fields introduced by the declaration capart of the declaration or in a constructor in the same class.

public const int WEIGHT = 1000;

public readonly int y = 5;


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const and readonly

const


readonly





public readonly int y;


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const and readonly

const


readonly





public readonly int y;


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Casting


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Casting

Direct Casting as Keyword


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void Example(object o){

// Casting

string 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

Whats the difference? Output?


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// Casting


// -OR-


// -OR-


}

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.


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// Casting


// -OR-


// -OR-


}

Casting


Number (2) Assigns null to s if o is not a string or if o is null. Otherwise assign to s CANT BE A NULL VALUEFor this reason, you cannot use it with value types.


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// Casting


// -OR-


// -OR-


}

Casting


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


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// Casting


// -OR-


// -OR-


}

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 can

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


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// I swear o is a string, C# compiler! Im ordering you to cast, I know what am


// I Donna know whether o is a string or not, try a cast and tell me!


// Am programming badly with this code!


}

Casting

Meaning!


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}

Casting

Meaning!

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


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}

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;


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g y ;

class MyClass1{}

class MyClass2{}

public class IsTest

{

public static void Main()

{ object[] myObjects = new object[6];

myObjects[0] = new MyClass1();


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;


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g y

class MyClass1{}

class MyClass2{}

public class IsTest

{


{ object[] myObjects = new object[6];



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 st

1:not a st

2:'hello'

3:not a st

4:not a st

5:not a st


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is Keyword


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is Keyword

The is operator is used to check whether the run-time type of an ocompatible with a given type.

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

expression is type


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is Keyword

Lets have the following example

class Class1{}

class Class2{}

public class IsTest{


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is Keyword{

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)

{


b = (Class2)o;

// do something with b

}

else

{

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

}}


{

Class1 c1 = new Class1();


Test(c1);

Test(c2);

Test("a string");

}

}

d

public class IsTest{


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is Keyword{

public static void Test(object o)

{

Class1 a;

Class2 b;

if (o is Class1)

{


a = (Class1)o;

// do something with a}

else if (o is Class2)

{


b = (Class2)o;

// do something with b

}

else

{

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

}}


{



Test(c1);

Test(c2);

Test("a string");

}

}

o is Class1

o is Class2

o is neither Class1

Press any key to co


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enum


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enum

As easy as:

And thats 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

}


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Exception Handling

E i Hi h


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Exception Hierarchy

E ti H dli


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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?

E ti H dli


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Exception Handling

using System;

using System.IO;

class tryCatchDemo


{

try

{


}

catch(Exception ex)

{


}}

}

The output?

E ti H dli


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Exception Handling

using System;

using System.IO;

class tryCatchDemo


{

try

{


}

catch(Exception ex)

{


}

}

}

The output?

Exception Handling Multiple catchs


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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


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Exception Handling

Multiple catch statement?!

catch(FileNotFoundException e)

{

Console.WriteLine(e.ToString());

}

catch(Exception ex)

{


}

Exception Handling finally keyword


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Exception Handling finally keywordclass FinallyDemo

{

static void Main(string[] args)

{

FileStream outStream = null;

FileStream inStream = null;

try

{

outStream = File.OpenWrite("DestinationFile.txt");

inStream = File.OpenRead("BogusInputFile.txt");

}

catch(Exception ex)

{


}

finally

{

if (outStream!= null)

{outStream.Close();

Console.WriteLine("outStream closed.");

}

if (inStream!= null)

{

inStream.Close();

Console.WriteLine("inStream closed.");

}

}

}

}


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Throwing Exceptions

Throwing Exceptions


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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


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Searching for a catch

Caller chain is traversed backwards until a method with a matching cfound.

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

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


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Creating Exceptions

Creating Exceptions


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Creating Exceptions

Lets 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.");

}


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Unsafe Code!

Unsafe Code!


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Unsafe Code!

unsafe code == (code using explicit pointers and memory allocation

// 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;

}


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Nullable Types


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Nullable Types - The Concept

Nullable Types


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Nullable Types

Declaration

DateTime? startDate;

Nullable Types


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Nullable Types

Declaration


// You can assign a normal value to startDate like this:

startDate = DateTime.Now;

Nullable Types


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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


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yp

Declaration

// Here's another example that declares and initializes a

nullable int:

int? unitsInStock = 5;

Nullable Types


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yp

class Program

{

static void Main()

{

DateTime? startDate = DateTime.Now;

bool isNull = startDate == null;

Console.WriteLine("isNull: " + isNull);

}

}

Nullable Types


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yp

class Program

{

static void Main()

{

DateTime? startDate = DateTime.Now;

bool isNull = startDate == null;

Console.WriteLine("isNull: " + isNull);

}

}

isNull: False

Press any key to continue...

Nullable Types


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yp

class Program

{

static void Main()

{

int i = null;

}

}

Nullable Types


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yp

class Program

{

static void Main()

{

int i = null;

}

}

Compiler error, Cant convert from null to type int


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using keywordusing Directive - using statem


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using Directive

using Directive


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The using Directive has two uses:

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

To create an alias for a namespace or a type:

using System.Text;

using Project = PC.MyCompany.Project;

using Directive


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namespace PC

{

// Define an alias for the nested namespace.


class A{

void M()

{

// Use the alias

Project.MyClass mc = new Project.MyClass();

}

}

namespace MyCompany

{namespace Project

{

public class MyClass { }

}

}

}

using Directive


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namespace PC

{



class A{

void M()

{

// Use the alias


}

}

namespace MyCompany

{namespace Project

{


}

}

}

using Directive


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namespace PC

{



class A{

void M()

{

// Use the alias


}

}

namespace MyCompany

{namespace Project

{


}

}

}

using Directive


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namespace PC

{



class A{

void M()

{

// Use the alias


}

}

namespace MyCompany

{namespace Project

{


}

}

}


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using statement

using statement


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C#, through the.NET Framework common language runtime (CLR), areleases the memory used to store objects that are no longer require

The release of memory is non-deterministic; memory is released whCLR decides to perform garbage collection. However, it is usually beslimited resources such as file handles and network connections as qupossible.

using Directive


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Defines a scope, outside of which an object or objects will be dispose

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

{// Use font1

}

using Directive


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Defines a scope, outside of which an object or objects will be dispose

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 Directive


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class 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();

}

}

using Directive


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{


{


}


{


}

}

class Program


{


{


}


Console.ReadLine();

}

}

using Directive


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{


{


}


{


}

}

class Program


{


{


}


Console.ReadLine();

}

}

using Directive


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{


{


}


{


}

}

class Program


{


{


}


Console.ReadLine();

}

}

using Directive


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{


{


}


{


}

}

class Program

{

static void Main()

{


{


}


Console.ReadLine();

}

}

using Directive


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{


{


}


{


}

}

class Program

{

static void Main()

{


{


}


Console.ReadLine();

}

}

using Directive


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{


{


}


{


}

}

class Program

{

static void Main()

{


{


}


Console.ReadLine();

}

}

Using limited resource...

Disposing limited resource

Now outside using stateme


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Type Aliases

Type Aliases


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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");


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Files

Files, One Shot Reading


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// 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);


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FilesReading and Writing on a Text-based Fil

Files


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StreamWriter

Object for writing a stream down

StreamReader

Object for reading a stream up

using System;

using System.IO;


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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);

}

}

}

}

using System;

using System.IO;

Hello

And

Welcome


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{


{




{




}



{

string s = "";


{


}

}

}

}

Press any key to c

using System;

using System.IO;

bli ti l l T t

Hello

And

Welcome

P k t


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{


{




{




}



{

string s = "";


{


}

}

}

}

Press any key to c

using System;

using System.IO;

class Test


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class Test

{


{


if (!File.Exists(path))

{// Create a file to write to.

using (StreamWriter sw = File.CreateText(path))

{




}

}


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

{

string s = "";


{


}

}

}

}

using System;

using System.IO;

class Test


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class Test

{


{





{




}

}



{

string s = "";


{


}

}

}

}

using System;

using System.IO;

class Test


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class Test

{


{





{




}

}



{

string s = "";


{


}

}

}

}

using System;

using System.IO;

class Test


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class Test

{


{





{




}

}



{

string s = "";


{


}

}

}

}

using System;

using System.IO;

class Test


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{


{




using (StreamWriter sw = File.CreateText(path)){




}

}


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

string s = "";


{


}

}

}

}

Reading and Writing on a Binary Files


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Reading and Writing on a Binary FilesBinaryWriter and BinaryReader

// Change the file path here to where you want it.

String path = @C:/Users/Mhd/Desktop/test1.txt;

FileStream fileStream = File.OpenWrite(path);

BinaryWriter binaryWriter = new BinaryWriter(fileStream);

binaryWriter.Write(2);

binaryWriter.Write("Hello");

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


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Class Diagram

Class Diagram


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Windows Forms


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Windows Forms


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


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Thats it for today!

Date post:	02-Jun-2018
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