EventHandler in C#

mironline

Dear Friends.

here is my code :

Expand|Select|Wrap|Line Numbers

 class test

{

    public event EventHandler RequestStart;

    public event EventHandler RequestFailed;
 
    public void Start(){

      RequestStart("string" , new EventArgs());

      return ; 

    }

}
 
class app

{
 
  public app(){

   test _t = new test();

   _t.RequestFailed += new EventHandler(fa);

   _t.Start();

   } 
 
    void fa(object sender, EventArgs e){}

}

I have a "Object reference not set to an instance of an object." exception in line : 7
What is problem ?

Thank you .
Ali.MZ

Plater

You did not assign a handler to RequestStart, but are trying to use it.

mironline

solution:

Expand|Select|Wrap|Line Numbers

 class test

{

    public event EventHandler RequestStart;

    public event EventHandler RequestFailed;
 
  protected virtual void OnRequestStart(...........)

        {

            if (RequestStart != null) RequestStart(........);

        }

    public void Start(){

      OnRequestStart("string" , new EventArgs());

      return ; 

    }

}
 
class app

{
 
  public app(){

   test _t = new test();

   _t.RequestFailed += new EventHandler(fa);

   _t.Start();

   } 
 
    void fa(object sender, EventArgs e){}

}

EventHandler in C#

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re: EventHandler in C#

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