Bug 45860 - “Control” Property In Custom Renderers and Effects Is Null For Layouts
Summary: “Control” Property In Custom Renderers and Effects Is Null For Layouts
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: unspecified
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Paul DiPietro [MSFT]
Depends on:
Reported: 2016-10-25 01:04 UTC by Hakan
Modified: 2017-08-04 13:33 UTC (History)
4 users (show)

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

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Description Hakan 2016-10-25 01:04:05 UTC
When I try to write a custom renderer for any of the layout classes, the "Control" property appears null. It is OK since the renderer already is the wrapper for the native control but it is a problem when creating an Effect. So I cannot do any customization with the layout classes using Effects since Control property is not assigned.
Comment 1 Paul DiPietro [MSFT] 2017-03-01 15:39:06 UTC
Can you upload a project example of what you're attempting to do? Are you using SetNativeControl() at all?
Comment 2 Hakan 2017-05-04 18:28:03 UTC
I am not using SetNativeControl. You can create a barebone custom renderer class for a ContentView and AbsoluteLayout to try debugging the Control property. It will always be null.

It is not a problem for custom renderers because we can access the corresponding native View since the renderer inherits from it but that is not the case for Effects.
Comment 3 Paul DiPietro [MSFT] 2017-05-04 19:14:35 UTC
You should use SetNativeControl. Similar to the docs (https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/custom-renderer/view/#Creating_the_Custom_Renderer_on_Android), you can have a custom renderer inherit from ViewRenderer<AbsoluteLayout, Android.Views.View> like this:

	public class TestLayoutRenderer : ViewRenderer<AbsoluteLayout, AView>
		protected override void OnElementChanged(ElementChangedEventArgs<AbsoluteLayout> e)
			if (Control == null)
				var view = new AView(this.Context);

I've just used this and the Control is not null after calling SetNativeControl.
Comment 4 Hakan 2017-05-05 01:59:02 UTC
I was familiar with that approach for complex renderers where the author is adding native controls into the renderer but I was thinking of a simple AbsoluteLayout renderer similar to a ButtonRenderer.

For example when I create a button renderer, Control property is already set, I don't have to do anything. I thought layouts would be the same. But apparently I am mistaken. Thanks for the clarification. 

I am using a ContentView render without setting any native controls. So now I wonder, how does that work? Should I be setting a native AView for that, too?

Is there a documentation or code sample that shows simple layout/contentview renderers for both Android and iOS? (Because I didn't know about AView etc. before, so such examples would be nice)