Bug 25020 - MouseEntered NSEvent causes assertion failure
Summary: MouseEntered NSEvent causes assertion failure
Alias: None
Product: Xamarin.Mac
Classification: Desktop
Component: Other ()
Version: 1.10.0
Hardware: PC Mac OS
: --- critical
Target Milestone: ---
Assignee: Chris Hamons
Depends on:
Reported: 2014-12-02 19:50 UTC by Cody Beyer (MSFT)
Modified: 2014-12-03 01:36 UTC (History)
2 users (show)

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

TestCase (23.17 KB, application/zip)
2014-12-02 19:50 UTC, Cody Beyer (MSFT)

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Description Cody Beyer (MSFT) 2014-12-02 19:50:17 UTC
Created attachment 8948 [details]

### Description

When calling an NSEvent within a MouseEntered event, there is an AssertionFailure

### Test Case


### Steps to Reproduce

1. Open attached test case
2. Run in Debug
3. Mouse over the main window
4. Notice failure in Application Output

### Error Details

>2014-12-02 16:46:39.941 MouseEnter[2838:727846] *** Assertion failure in -[NSEvent clickCount], /SourceCache/AppKit/AppKit-1343.16/AppKit.subproj/NSEvent.m:1636
>2014-12-02 16:46:39.942 MouseEnter[2838:727846] Invalid message sent to event "NSEvent: type=MouseEntered loc=(290.188,352.395) time=20614.8 flags=0x100 win=0x6e8a400 winNum=10055 ctxt=0x22283 evNum=2292 trackNum=2bb810 userData=0x0"
>2014-12-02 16:46:39.943 MouseEnter[2838:727846] 

### Version

=== Xamarin Studio ===

Version 5.5.4 (build 15)
Installation UUID: 3e4348fa-e0b3-46a4-8426-58f27e19159e
	Mono 3.10.0 ((detached/92c4884)
	GTK+ 2.24.23 (Raleigh theme)

	Package version: 310000031

=== Apple Developer Tools ===

Xcode 6.1 (6604)
Build 6A1052d

=== Xamarin.iOS ===

Version: (Business Edition)
Hash: 840a925
Build date: 2014-11-16 21:03:22-0500

=== Xamarin.Android ===

Version: (Business Edition)
Android SDK: /Users/codybeyer/Library/Developer/Xamarin/android-sdk-macosx
	Supported Android versions:
		2.1    (API level 7)
		2.2    (API level 8)
		2.3    (API level 10)
		3.1    (API level 12)
		4.0    (API level 14)
		4.0.3  (API level 15)
		4.1    (API level 16)
		4.2    (API level 17)
		4.4    (API level 19)
		4.4.87 (API level 20)
Java SDK: /usr
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

=== Xamarin.Mac ===

Version: (Business Edition)

=== Build Information ===

Release ID: 505040015
Git revision: f93940a35458a18052f1a25e106e62ca970d9c40
Build date: 2014-11-19 15:32:41-05
Xamarin addins: dc23cbd91a3a0e1d326328e1229e86c942a49ec8

=== Operating System ===

Mac OS X 10.10.1
Darwin Codys-MacBook-Pro.local 14.0.0 Darwin Kernel Version 14.0.0
    Fri Sep 19 00:26:44 PDT 2014
    root:xnu-2782.1.97~2/RELEASE_X86_64 x86_64
Comment 1 Chris Hamons 2014-12-03 01:36:27 UTC
So, I'm marking this bug invalid, as we're echoing what the underlying runtime is doing. However, I realize that isn't very helpful, so let me explain.

If you do the same thing your example does in objective-c:


You'll get the same assertion:


Now the deeper and more interesting question, is why are you seeing this. Let's take look at the documentation:


"Raises an NSInternalInconsistencyException if sent to a non-mouse event." "The return value of this method is meaningless for events other than mouse-down or mouse-up events."

Since you can send any message to any objective-c instance, and NSEvent is a base type of many events that could occur, Apple could have chosen to have "invalid" selectors, such as clickCount on an event that isn't related to clicking, act as any other does not respond message. However, Apple has chosen to throw this assert to help you figure out that you are treating this NSEvent incorrectly.

These are the only valid messages to send to any NSEvent:


The exposed C# properties are somewhat straightforward to find. 

Beyond that, you need to check the type of the event and only query properties that make sense for that type.

The NSEvent API that apple exposed (and Xamarin.Mac exposed to c#) is less pleasant than many other APIs where the specific events only have properties for the valid event type. 

As a side note, this also means that expanding an NSEvent inside the debugger may/will cause your application to crash. This is unfortunate, and a known issue. We're working with the XS team to fix this long term.