Custom event handler not getting initialized

Question

Following is the Code i am using

class ImpersonatedTab : System.Windows.Forms.TabPage  
    {
        Credentials _cred = new Credentials();

        public delegate void Savesetting(TabData Tb);
        public event Savesetting TriggerSaveSetting;


        public ImpersonatedTab(TabData tb)
        {          
            ........
        }

        private void SaveData()
        {
            TriggerSaveSetting(_tabdata);
        }

       private Onclick()
       {
         SaveData();
       }


     }

When i call Onclick function within ImpersonatedTab class it returns error saying TriggerSaveSetting is null

I initialize this call like

ImpersonatedTab Tab = new ImpersonatedTab(tb);
Tab.TriggerSaveSetting += new ImpersonatedTab.Savesetting(Tab_TriggerSaveSetting);

i have created events earlier, but am not able to figure out whats wrong with this one.. i am sure should be some silly mistake.

Answer 1

One possible case where this could happen is if you try to call the event from within the constructor of the ImpersonatedTab class. There where you put those ... . Also it is a good practice to check if the event handler has been initialized before calling it.

Answer 2

Change your code to this:

    public delegate void Savesetting(TabData Tb);
    private Savesetting saveSettingDlg;

    public event Savesetting TriggerSaveSetting {
        add { saveSettingDlg += value; }
        remove { saveSettingDlg -= value; }
    }

    private void SaveData() {
        var handler = saveSettingDlg;
        if (handler != null) handler(_tabdata);
    }

You can now set a breakpoint on the add accessor and SaveData() and verify that event subscription is working correctly. If you do see the add accessor getting called but still get a null for handler then there's a problem with the object reference.

Answer 3

You are trying to invoke the TriggerSaveSetting event handlers before any handler was attached to it. Make sure, to check, the event has been some handlers attached:

private void OnTriggerSaveSetting(_tabdata)
{
    if (TriggerSaveSetting != null)
        TriggerSaveSetting(_tabdata);
}