website/archived/monotouch_events.md

title	lastmodified	redirect_from
MonoTouch Events	2009-08-05	/MonoTouch_Events/

MonoTouch Events

If you want to intercept events from UIControl, you have a range of options: from using the C# lambdas and delegate functions to using the low-level Objective-C APIs.

The following shows how you would capture the TouchDown event on a button, depending on how much control you need:

C# Style

Using the delegate syntax:

UIButton button = MakeTheButton ();
button.TouchDown += delegate {
    Console.WriteLine ("Touched");
};

If you like lambdas instead:

button.TouchTown += () => {
   Console.WriteLine ("Touched");
};

If you want to have multiple buttons use the same handler to share the same code:

void handler (object sender, EventArgs args)
{
   if (sender == button1)
      Console.WriteLine ("button1");
   else
      Console.WriteLine ("some other button");
}
 
button1.TouchDown += handler;
button2.TouchDown += handler;

Monitoring more than one kind of Event

The C# events for UIControlEvent flags have a one to one mapping to individual flags. Sometimes you might want to have the same piece of code handle two or more events, in that case, use the UIControl.AddTarget method:

button.AddTarget (handler, UIControlEvent.TouchDown | UIControl.TouchCancel);

Using the lambda syntax:

button.AddTarget (()=> Console.WriteLine ("An event happened"), UIControlEvent.TouchDown | UIControl.TouchCancel);

If you need to use low-level features of Objective-C, like hooking up to a particular object instance and invoke a particular selector:

[Export ("MySelector")]
void MyObjectiveCHandler ()
{
    Console.WriteLine ("Hello!");
}
 
// In some other place:
 
button.AddTarget (this, new Selector ("MySelector"), UIControlEvent.TouchDown);