C# EventHandlers... | Tech Off

ploe

Is there a difference between these two lines?

button.Click += new EventHandler(OnButtonClick);
button.Click += OnButtonClick;

Both compile and work from what I can see. Do they behave differently? Is one preferred over the other?

Yggdrasil
Pour me a cab, 'cause I can't drink no more.

They're identical. The second is simply a compiler trick that infers the right delegate automatically, so behind the scenes the second form is converted to the first.

Ion Todirel
buuu

In reply to Yggdrasil

#Jun 25th, 2008 @ 7:19 AM

yea, added in C# 2.0 and called "delegate inference" or something close to that...

littleguru
<3 Seattle

In reply to Yggdrasil

#Jun 25th, 2008 @ 7:19 AM

Exactly... using ILDASM will show you that both are the same once compiled.

Bas
It finds lightbulbs.

Why does Visual Studio still come up with the "New EventHandler(button_Click); (Press tab to insert)" tooltip when that approach is no longer necessary?

evildictaitor
if( !succeed( try() ) ) { while(true) try(); }

In reply to Bas

#Jun 26th, 2008 @ 4:32 AM

For big functions it's still nice, and you'll notice that at the point where TAB builds the stub, it's also got the button_Click bit highlighted, so you can immediately type (o,e) => someFunc(e)

TommyCarlier
I want my scalps!

In reply to evildictaitor

#Jun 26th, 2008 @ 5:39 AM

And if you press tab a second time, the method is created for you!

Bas
It finds lightbulbs.

In reply to evildictaitor

#Jun 26th, 2008 @ 5:39 AM

So why didn't they change it to just say "button_Click(); (Press Tab to insert)"?

evildictaitor
if( !succeed( try() ) ) { while(true) try(); }

In reply to Bas

#Jun 26th, 2008 @ 6:39 AM

I suspect they just haven't implemented it yet.

If they're sensible they should have it as an option, because lovely as lambda functions are, not everyone likes them.

The bit that impressed me was that lambda functions are in fact entirely syntactic sugar, and therefore also work under .NET 2.0, so you're right, there's a good argument that this should be changed in future versions of VS/C#.

TommyCarlier
I want my scalps!

In reply to evildictaitor

#Jun 26th, 2008 @ 6:58 AM

You can even make extension methods work in .NET 2.0, if you use a little (unsupported) trick.

Bas
It finds lightbulbs.

In reply to TommyCarlier

#Jun 26th, 2008 @ 7:08 AM

I get a 404 there. But you can actually get a lot of purely syntactic stuff, like automatic properties and such, to work in .NET 2.0 if you just use a 3.0 compiler and target the 2.0 framework. Does it work like that?

TommyCarlier
I want my scalps!

In reply to Bas

#Jun 26th, 2008 @ 7:24 AM

I fixed the link.

The problem is that the compiler needs the ExtensionAttribute-class, which is implemented in System.Core.dll (new in .NET 3.5). The solution is to add a class named ExtensionAttribute with the namespace System.Runtime.CompilerServices to your project. Like this:

namespace System.Runtime.CompilerServices
{
    public class ExtensionAttribute : Attribute { }
}