Indexer in C #

The ndexer in C # helps index objects, such as an array. When you define an indexer for a class, this class operates similarly to a virtual array . Then you can access the instance of this class with the array access operator in C # ([]).

Indexer syntax

In C #, one-way Indexer has the following syntax:

 
ki ể u_ph ầ n_t ử this [ int index ] { get { // trả về giá trị được xác định bởi index } set { // thiết lập giá trị được xác định bởi index } } 

Use Indexer in C #

Indexer behavior declaration is similar to attribute declaration. You use get and set to define an Indexer. However, the properties return or set a specific data member, but, the Indexer returns or sets a specific value from the instance of the object. In other words, it divides instance data into smaller parts and indexes each section, grabs or sets each section.

The difference is, you need to provide the attribute name when declaring the attribute, and the Indexer needs the name, you only need the this keyword to refer to the instance of the object. The following example illustrates this:

 using System ; namespace QTMCSharp { class IndexedNames { private string [] danhSachTen = new string [ size ]; static public int size = 10 ; public IndexedNames () { for ( int i = 0 ; i < size ; i ++) danhSachTen [ i ] = "N. A." ; } public string this [ int index ] { get { string tmp ; if ( index >= 0 && index <= size - 1 ) { tmp = danhSachTen [ index ]; } else { tmp = "" ; } return ( tmp ); } set { if ( index >= 0 && index <= size - 1 ) { danhSachTen [ index ] = value ; } } } static void Main ( string [] args ) { IndexedNames names = new IndexedNames (); names [ 0 ] = "Anh" ; names [ 1 ] = "Hoàng" ; names [ 2 ] = "Hoa" ; names [ 3 ] = "Thám" ; names [ 4 ] = "Bình" ; names [ 5 ] = "Định" ; names [ 6 ] = "Vương" ; for ( int i = 0 ; i < IndexedNames . size ; i ++ ) { Console . WriteLine ( names [ i ]); } Console . ReadKey (); } } } 

Compiling and running the C # program on your side will have the following results:

 Brother 
 Hoang 
 flower 
 Detective 
 jar 
 Dinh 
 Wang 
 NA 
 NA 
 NA 

Load Indexer stack in C #

Indexer can be overloaded in C #. Indexer can also be declared with multiple parameters and each parameter can be a different type. Indexers are not necessarily integers. C # allows indexes to be other value types, such as strings.

The following example will illustrate how to load Indexer in C #:

 using System ; namespace IndexerApplication { class IndexedNames { private string [] danhSachTen = new string [ size ]; static public int size = 10 ; public IndexedNames () { for ( int i = 0 ; i < size ; i ++) { danhSachTen [ i ] = "N. A." ; } } public string this [ int index ] { get { string tmp ; if ( index >= 0 && index <= size - 1 ) { tmp = danhSachTen [ index ]; } else { tmp = "" ; } return ( tmp ); } set { if ( index >= 0 && index <= size - 1 ) { danhSachTen [ index ] = value ; } } } public int this [ string name ] { get { int index = 0 ; while ( index < size ) { if (danhSachTen [ index ] == name ) { return index ; } index ++; } return index ; } } static void Main ( string [] args ) { IndexedNames names = new IndexedNames (); names [ 0 ] = "Anh" ; names [ 1 ] = "Hoàng" ; names [ 2 ] = "Hoa" ; names [ 3 ] = "Thám" ; names [ 4 ] = "Bình" ; names [ 5 ] = "Định" ; names [ 6 ] = "Vương" ; //sử dụng indexer đầu tiên với tham số int for ( int i = 0 ; i < IndexedNames . size ; i ++) { Console . WriteLine ( names [ i ]); } //sử dụng indexer thứ 2 với tham số string Console . WriteLine ( names [ "Vương" ]); Console . ReadKey (); } } } 

Running the code above we will get the following result:

 Brother 
 Hoang 
 flower 
 Detective 
 jar 
 Dinh 
 Wang 
 NA 
 NA 
 NA 
 6 

According to Tutorialspoint

Previous article: Reflection in C #

Next article: Delegate in C #