Bug 2441 - InvalidCastException in CALayer.ActionForKey(System.String eventKey)
Summary: InvalidCastException in CALayer.ActionForKey(System.String eventKey)
Alias: None
Product: iOS
Classification: Xamarin
Component: Xamarin.iOS.dll ()
Version: 5.0
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2011-12-09 14:34 UTC by Jon Lipsky
Modified: 2011-12-19 16:03 UTC (History)
3 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Jon Lipsky 2011-12-09 14:34:16 UTC
I'm receiving the following exception when I try to override the "ActionForKey" method in the CALayer class.  Specifically, I get this exception when calling "base.ActionForKey(eventKey)".

[FATAL] Unable to cast object of type 'MonoTouch.CoreAnimation.CABasicAnimation' to type 'MonoTouch.CoreAnimation.CAAction'.
System.InvalidCastException: Unable to cast object of type 'MonoTouch.CoreAnimation.CABasicAnimation' to type 'MonoTouch.CoreAnimation.CAAction'.
  at MonoTouch.CoreAnimation.CALayer.ActionForKey (System.String eventKey) [0x00049] in /Developer/MonoTouch/Source/monotouch/src/CoreAnimation/CALayer.g.cs:601
Comment 1 Rolf Bjarne Kvinge [MSFT] 2011-12-09 19:07:58 UTC
According to Apple's documentation the return value for actionForKey: must implement the CAAction protocol. CABasicAnimation does implement the CAAction protocol, but the managed CABasicAnimation class doesn't (and can't) inherit from the (managed) CAAction class. This means that this exception is thrown when managed code tries to cast the returned CABasicAnimation instance to CAAction.

In short: ActionForKey's return type is wrong, it should be declared as NSObject, since it can actually be any object. Unfortunately this is a breaking change.

Miguel: how can this best be solved? ActionForKey is apparently unusable as it is, so I think this breaking change should be ok.
Comment 2 Miguel de Icaza [MSFT] 2011-12-09 22:01:19 UTC
Agreed, we need to change the return to be NSObject and deal with it that way.
Comment 3 Rolf Bjarne Kvinge [MSFT] 2011-12-12 18:06:39 UTC
Jon, do you have some sample code I can use to create a test case out of?
Comment 4 Jon Lipsky 2011-12-12 18:35:39 UTC
Here's the test class I created to test this on my machine:

public class TestLayer : CALayer
    	public bool AnimationsEnabled {get;set;}
        public TestLayer () : base()
        	AnimationsEnabled = true;    
        public override CAAction ActionForKey (string eventKey)
            if (AnimationsEnabled)
            	return base.ActionForKey(eventKey);
            return null;
        public override void DrawInContext (CGContext ctx)
            // Do anything here with the context  

I just added an instance of that layer to a UIView and called "SetNeedsDisplay()"
Comment 5 Rolf Bjarne Kvinge [MSFT] 2011-12-15 09:55:19 UTC
Fixes committed (maccore/f997c11). I also found a few more properties using CAAction which I also fixed. This will be included in the next beta (5.1.2).

In the meantime you can use this as a workaround:

[Export ("actionForKey:")]
public new NSObject ActionForKey (string eventKey)
  return Runtime.GetNSObject (Messaging.IntPtr_objc_msgSendSuper_IntPtr (SuperHandle, new Selector ("actionForKey:").Handle, new NSString (eventKey).Handle));

Note that the fixes will change the signature of ActionForKey, so you'll get a compiler error with the current ActionForKey overload once you upgrade.

Thanks for the test case!