Bug 34016 - InvalidOperationException should be thrown when calling getter of C# delegate event properties if delegate class property is already set
Summary: InvalidOperationException should be thrown when calling getter of C# delegate...
Alias: None
Product: Xamarin.Mac
Classification: Desktop
Component: Other ()
Version: 2.0.2
Hardware: Macintosh Mac OS
: Normal normal
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2015-09-16 15:15 UTC by Sandy Armstrong [MSFT]
Modified: 2016-09-26 21:59 UTC (History)
2 users (show)

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

Simple test case (12.12 KB, application/zip)
2015-09-16 15:15 UTC, Sandy Armstrong [MSFT]

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Description Sandy Armstrong [MSFT] 2015-09-16 15:15:27 UTC
Created attachment 12917 [details]
Simple test case

In Xamarin.Mac, when handling view events, you are not supposed to mix using delegate classes with using C# delegate events.  An InvalidOperationException helps to prevent this. For example, if I do the following, I will get an exception on the last line:

			var tv = new NSTableView ();
			tv.Delegate = new NSTableViewDelegate();
			var cgrv = tv.CoreGetRowView;

This is good. It prevents the NSTableView.Delegate we set from getting messed with.

However, the exception fails to get thrown if I am working with the subclass NSOutlineView:

			var ov = new NSOutlineView ();
			ov.Delegate = new NSOutlineViewDelegate();
			var cgrv = ov.CoreGetRowView;
			// Now ov.Delegate shows as null

Accessing the getter of the C# delegate event property causes the underlying delegate class to be replaced. It's especially confusing because it's replaced with an NSTableViewDelegate, and therefore can only be accessed by downcasting the NSOutlineView to an NSTableView. NSOutlineView.Delegate returns null.

We came across this while working on the inspector, which inspects property values for selected view. View event handling would break simply by accessing the getters on these C# delegate event properties.

Test case attached.