شرح ال Indexer

أخواني ،، احببت ان أشرح القليل عن الـ Indexer لأني تغلبت لما فهمته .. و ان شالله تعم الفائده ،،

و أنا جاهز لاي استفسار ...

بسم الله نبدأ ،،

Indexer

كما هو معروف ،، فإن الـ Class يستخدم This كــــ keyword ،، و ذلك لتعريف الاندكسير Indexer ،،

و هذا من شأنه السماح للـ array بالوصول الى العناصر و المتغيرات بالـClass

allow array-style indexed access to lists of elements in a class

الـ Syntax للـ Indexer كالتالي :

accessModifier returnType this[ IndexType1 name1, IndexType2 name2, … ]
{	
   get	
			 {		  // use name1, name2, ... here to get data   }
  set	   
			 {		// use name1, name2, ... here to set data	}
}

كن حذراً .. فإن تعريف الـ Indexer كـــ Static هو : syntax Error

و هذا مثال للتوضيح ،،

	1	//  Box.cs
	2	// Box class definition represents a box with length, 
	3	// width and height dimensions with indexers.
	4	public class Box
	5	{
	6	   private string[] names = { "length", "width", "height" };
	7	   private double[] dimensions = new double[ 3 ];
	8	
	9	   // constructor
	10	   public Box( double length, double width, double height )
	11	   {
	12		  dimensions[ 0 ] = length;
	13		  dimensions[ 1 ] = width;
	14		  dimensions[ 2 ] = height;
	15	   }
	16	
	17	   // indexer to access dimensions by integer index number
	18	   public double this[ int index ]							 
	19	   {														   
	20		  get													  
	21		  {														
	22			 // validate index to get							  
	23			 if ( ( index < 0 ) || ( index >= dimensions.Length ) )
	24				return -1;										 
	25			 else												  
	26				return dimensions[ index ];						
	27		  } // end get											 
	28		  set													  
	29		  {														
	30			 if ( index >= 0 && index < dimensions.Length )		
	31				dimensions[ index ] = value;					   
	32		  } // end set											 
	33	   } // end numeric indexer									
	34	
	35	   // indexer to access dimensions by their string names				  
	36	   public double this[ string name ]						 
	37	   {														 
	38		  get													
	39		  {													  
	40			 // locate element to get							
	41			 int i = 0;										  
	42			 while ( ( i < names.Length ) &&					 
	43				( name.ToLower() != names[ i ] ) )			   
	44				i++;											 
	45																 
	46			 return ( i == names.Length ) ? -1 : dimensions[ i ];
	47		  } // end get										   
	48		  set													
	49		  {													  
	50			 // locate element to set							
	51			 int i = 0;										  
	52			 while ( ( i < names.Length ) &&					 
	53				( name.ToLower() != names[ i ] ) )			   
	54				i++;											 
	55																 
	56			 if ( i != names.Length )							
	57				dimensions[ i ] = value;						 
	58		  } // end set										   
	59	   } // end string indexer								   
	60	} // end class Box

Box.cs

1	//BoxTest.cs
	2	// Indexers provide access to a Box object's members.
	3	using System;
	4	
	5	public class BoxTest
	6	{
	7	   public static void Main( string[] args )
	8	   {
	9		  // create a box
	10		  Box box = new Box( 30, 30, 30 );
	11	
	12		  // show dimensions with numeric indexers
	13		  Console.WriteLine( "Created a box with the dimensions:" );
	14		  Console.WriteLine( "box[ 0 ] = {0}", box[ 0 ] );
	15		  Console.WriteLine( "box[ 1 ] = {0}", box[ 1 ] );
	16		  Console.WriteLine( "box[ 2 ] = {0}", box[ 2 ] );
	17	
	18		  // set a dimension with the numeric indexer
	19		  Console.WriteLine( "\nSetting box[ 0 ] to 10...\n" );
	20		  box[ 0 ] = 10;
	21	
	22		  // set a dimension with the string indexer
	23		  Console.WriteLine( "Setting box[ \"width\" ] to 20...\n" );
	24		  box[ "width" ] = 20;
	25	
	26		  // show dimensions with string indexers
	27		  Console.WriteLine( "Now the box has the dimensions:" );
	28		  Console.WriteLine( "box[ \"length\" ] = {0}", box[ "length" ] );
	29		  Console.WriteLine( "box[ \"width\" ] = {0}", box[ "width" ] );
	30		  Console.WriteLine( "box[ \"height\" ] = {0}", box[ "height" ] );
	31	   } // end method Main
	32	} // end class BoxTest

BoxTest.cs

أما نتيجة التنفيذ ،، فهي كالتالي :

Created a box with the dimensions:
box[ 0 ] = 30
box[ 1 ] = 30
box[ 2 ] = 30

Setting box[ 0 ] to 10...

Setting box[ "width" ] to 20...

Now the box has the dimensions:
box[ "length" ] = 10
box[ "width" ] = 20
box[ "height" ] = 30

أتمنى أن يكون واضح ،،