Delegates: How to check for target methods

[Einar Høst]

Hi,

I'm using delegates to show progress when performing certain tasks. However,
I'd like to check to see that there actually is a method available for the
delegate to call. What's the correct way of doing that? Looking at the
documentation for delegates, I've come up with:

if (MyEvent.Target != null)
{
MyEvent(this, new MyEventArgs());
}

Still, this would be correct for instance methods only, right? Would this be
better?

if (MyEvent.Method != null)
{
MyEvent(this, new MyEventArgs());
}

Thanks,
Einar.

--
"If it was so, it might be; and if it were so, it would be; but as it isn't,
it ain't. That's logic" -- Lewis Carroll

[Jon Skeet [C# MVP]]

Einar Høst <_e*******@hotmail.com> wrote:

I'm using delegates to show progress when performing certain tasks. However,
I'd like to check to see that there actually is a method available for the
delegate to call. What's the correct way of doing that? Looking at the
documentation for delegates, I've come up with:

if (MyEvent.Target != null)
{
MyEvent(this, new MyEventArgs());
}

Still, this would be correct for instance methods only, right? Would thisbe
better?

if (MyEvent.Method != null)
{
MyEvent(this, new MyEventArgs());
}

Could you give an example of how you'd construct a delegate which
*didn't* have a method to call?

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Mattias Sjögren]

Einar,

However,
I'd like to check to see that there actually is a method available for the
delegate to call.

As long as the delegate isn't a null reference there is at least one
method to call, so you just have to do

MyEventHandler h = MyEvent;
if ( h != null )
h(this, new MyEventArgs());

Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Kjetil Bjerknes]

"Einar Høst" <_e*******@hotmail.com> wrote in message news:<eq**************@TK2MSFTNGP09.phx.gbl>...

Hi,

I'm using delegates to show progress when performing certain tasks. However,
I'd like to check to see that there actually is a method available for the
delegate to call. What's the correct way of doing that? Looking at the
documentation for delegates, I've come up with:

if (MyEvent.Target != null)
{
MyEvent(this, new MyEventArgs());
}

Still, this would be correct for instance methods only, right? Would this be
better?

if (MyEvent.Method != null)
{
MyEvent(this, new MyEventArgs());
}

Thanks,
Einar.

You should simply check if the delegate variable is null. An example:

[...]
private delegate void MyEventDelegate();

private MyEventDelegate myEvent;

private void button2_Click(object sender, System.EventArgs e) {
if (myEvent != null) {
myEvent();
} else {
Console.WriteLine("Empty Delegate. Adding methods");
myEvent += new MyEventDelegate(MyStaticMethod);
myEvent += new MyEventDelegate(MyInstanceMethod);
}
}

private static void MyStaticMethod() {
Console.WriteLine("Hello from MyStaticMethod()");
}

private void MyInstanceMethod() {
Console.WriteLine("Hello from MyInstanceMethod()");
}
[...]

[Einar Høst]

Hi, thanks for responses, I believe 'if (MyEvent != null)' does the trick.
Obviously, I'm new to the whole delegate thing, so my understanding of it is
a bit muddled.

- Einar