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

Question

Hi, 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 button click, in the subscriber method, there is always "EventArgs e" parameter. Can I create somehow the method that will pass data this way, I mean they will be passed in the base Eventargs?

Answer 1

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.

Answer 2

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);