Bug 16800 - Rx Observable.FromEventPattern doesn't work in Release mode on Android 4.3
Summary: Rx Observable.FromEventPattern doesn't work in Release mode on Android 4.3
Status: RESOLVED FEATURE
Alias: None
Product: Android
Classification: Xamarin
Component: Bindings ()
Version: 4.10.1
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: ---
Assignee: Atsushi Eno
URL:
Depends on:
Blocks:
 
Reported: 2013-12-14 10:26 UTC by Jakub Arnold
Modified: 2013-12-16 03:30 UTC (History)
1 user (show)

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

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Status:
RESOLVED FEATURE

Description Jakub Arnold 2013-12-14 10:26:59 UTC
I have a simple activity with a TextView. The following code
    
    Observable.FromEventPattern<TextChangedEventArgs>(textbox, "TextChanged");

works just fine in Debug configuration, but if I switch to release it fails with

    [mono-rt] [ERROR] FATAL UNHANDLED EXCEPTION: System.InvalidOperationException: Could not find event 'TextChanged' on object of type 'Android.Widget.TextView'.
Comment 1 Atsushi Eno 2013-12-14 23:33:59 UTC
Because you have to specify linking description.
http://docs.xamarin.com/guides/android/advanced_topics/linking/

Observable.FromEventPattern() specifies event by name, thus gets the member using reflection, which doesn't count the member to preserve.
Comment 2 Jakub Arnold 2013-12-15 04:26:43 UTC
If I understand this correctly the linker will strip away the `TextChanged` event from the textbox, because I'm not referencing it directly.

But I'm not sure how to use the [Preserve] annotation for a builtin type such as TextView. It seems that the only way to make this work is by fake-assigning an event handler (as the guide suggests).

	var ignore = false;
	if (ignore)
	{
		searchBox.TextChanged += (sender, e)
		{
		};				
	}

Isn't there a more clean way to do this? If I omit the `ignore` var the compiler complains with unreachable code warning, and I can't really make an empty lambda expression without { }
Comment 3 Atsushi Eno 2013-12-16 03:30:05 UTC
[Preserve] is not applicable if you don't own the sources of the library. TextView is in Mono.Android.dll and you don't build it, so this attribute is not for you.

With Custom Linking with LinkDescription xml, you don't have to make your code dirty.