It is possible to pass data to EventArgs without creating derived class?

Question

I am a bit confused. I know I can create class derived from EventArgs in order to have custom event data. But can I employ the base class EventArgs somehow? Like the mouse butto

Answer 1

Is it possible to just use the EventArgs datatype raw? Absolutely. According to MSDN:

This class contains no event data; it is used by events that do not pass state information to an event handler when an event is raised. If the event handler requires state information, the application must derive a class from this class to hold the data.

http://msdn.microsoft.com/en-us/library/system.eventargs.aspx

    private event TestEventEventHandler TestEvent;
    private delegate void TestEventEventHandler(EventArgs e);

    private void button1_Click(object sender, EventArgs e)
    {
        TestEvent += TestEventHandler;
        if (TestEvent != null)
        {
            TestEvent(new EventArgs());
        }
    }
    private void TestEventHandler(EventArgs e)
    {
        System.Diagnostics.Trace.WriteLine("hi");
    }

Should you ever do it? Not for any reason I can think if. If you want to create your own clicks you can just instantiate the MouseEventArgs on your own, too:

MouseEventArgs m = new MouseEventArgs(System.Windows.Forms.MouseButtons.Left, 1, 42, 42, 1);

Answer 2

You can use the EventArgs class through the Generic Types approach. In this sample, i will use the Rect class with as return type:

public EventHandler<Rect> SizeRectChanged;

Raising the event:

if(SizeRectChanged != null){
   Rect r = new Rect(0,0,0,0);
   SizeRectChanged(this,r);
}

Listening the event:

anyElement.SizeRectChanged += OnSizeRectChanged;

public void OnSizeRectChanged(object sender, Rect e){
    //TODO abything using the Rect class
    e.Left = e.Top = e.Width = e.Height = 50;
}

So, don't need to create new events classes or delegates, simply create a EventHandler passing the specific type T.

Answer 3

Nope. The EventArgs base class is just a way to allow for some standard event delegate types. Ultimately, to pass data to a handler, you'll need to subclass EventArgs. You could use the sender arg instead, but that should really be the object that fired the event.