ContentView: Setting the ControlTemplate dynamically causes the control to disappear

[vanka78bg]

Description

I have noticed that ContentView does not support setting the ControlTemplate dynamically at runtime. When the ControlTemplate is set initially in XAML or in the Page's constructor, everything works as expected. When the ControlTemplate is set at a later stage, the ContentView just disappears. Some preliminary investigation leads me to conclude this has something to do with the ContentViews Handler. If the Handler is not created yet, setting the ControlTemplate would work as expected. If the Handler is already created, setting the ControlTemplate would make the control disappear.

While debugging, I have also noticed the ContentView inherits from the legacy Layout class. Setting the ControlTemplate at runtime would invalidate the measure, but calling IView.Measure after that on the ContentView would always return a zero Size. This might be some incompatibility between the old and the new layout systems, but I have not investigated that further.

Steps to Reproduce

1. Run the attached sample project
   • The first ContentView has a ControlTemplate set in XAML
   • The second ContentView has a custom Style specifying a ControlTemplate in XAML
   • The third and fourth ContentViews do not have a ControlTemplate specified initially
2. Click the Set Custom Template button
   • This sets a ControlTemplate to the third ContentView. Notice the ContentView disappearing.
3. Click the Set Custom Style button
   • This sets a Style specifying a ControlTemplate to the fourth ContentView. Notice the ContentView disappearing.

Version with bug

Preview 11

Last version that worked well

Unknown/Other

Affected platforms

iOS, Android, Windows, macOS

Affected platform versions

I have not tested on various versions of the different platforms.

Did you find any workaround?

The only workaround I have found so far is to replace the ContentView with a new instance, that has the desired ControlTemplate set initially. This is rather inconvenient, as changing the Style of a ContentView to a new one, which might potentially update the ControlTemplate, would require re-creating the entire ContentView every time, to avoid the bug.

Relevant log output

No log output available at this time.

Sample project

TestApp.zip

[Amir-Care]

Repro on VS 17.2.0 Preview 2.0 [32208.484.main]

[mfe-]

I'm having the same issue on the Windows Platform. Can't change the ControlTemplate during runtime.

                <!--<controls:CardView.Triggers>
                    <DataTrigger Binding="{Binding Player2Container.SelectedCardPlayer,Converter={StaticResource IsNullConverter}}" Value="True" 
                                 TargetType="{x:Type controls:CardView}">
                        <Setter Property="ControlTemplate" Value="{StaticResource CardViewBackControlTemplate}" />
                    </DataTrigger>
                    <DataTrigger Binding="{Binding Player2Container.SelectedCardPlayer,Converter={StaticResource IsNullConverter}}" Value="False" 
                                 TargetType="{x:Type controls:CardView}">
                        <Setter Property="ControlTemplate" Value="{StaticResource CardViewControlTemplate}" />
                    </DataTrigger>
                </controls:CardView.Triggers>-->

Setting it from Codebehind also doesn't change the appearance of the control.
I'm using Visual Studio 17.3.0 Preview 1.0