How to determine if there are any event handlers for DataGridView.CellFormatting event?

Question

I'm writing a control which inherits from a DataGridView. One of the things I would like to do is to handle the bug whereby a column's format provider is not used without handling the CellFormatting event (and doing the formatting myself) .

I thought I would write an "OnCellFormatting" method which says "if there's a column format provider, and there's no CellFormatting event handler(s), do the formatting" .

The important bit (I thought) was "...and there's no CellFormatting event handler" .

Now, in the past when I've written controls with events, I've done something like this:

  public event EventHandler SomethingHappened;

  protected void OnSomethingHappened(EventArgs e)
  {
     EventHandler handler = this.SomethingHappened;
     if (handler != null) handler(this, e);
  }

This works fine and my understanding is that this pattern determines if handlers are attached to the event and, if so, invoke those handlers. Fair enough, but why can't I do this:

  protected void OnCellFormatting(EventArgs e)
  {
     EventHandler handler = this.CellFormatting;
     if (handler == null) DoSomething();
  }

The error is "The event 'System.Windows.Forms.DataGridView.CellFormatting' can only appear on the left hand side of += or -="

What's different about this (type of) event ?

If I go to the definition of the event, and create my own, ie.

public event DataGridViewCellFormattingEventHandler CellFormatting2

...the compiler is quite happy to assign this to my "handler" variable, so my question is - what's different with the CellFormatting event (and, one presumes, many others) that I cannot determine if there are any event handlers for it ?

Thanks, Ross

Answer 1

Only the class that declares the event has full access to it.

For instance, you cannot invoke an event from other classes - even derived ones.

You are in this situation, because you are deriving from DataGridView .

---

You may be able to use reflection:

How do I raise an event via reflection in .NET (c#)?

MSDN: Type.GetEvent Method

Answer 2

That shows the assignment can't be performed because it's read only. May be you can try declaring the handler private?