[BUG] Binding does not work for Platform dependent Behaviors

[rachelkang]

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Issue moved from dotnet/maui#11729

• Please respond to @YMichurin.

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From @YMichurin on Tuesday, November 29, 2022 4:07:21 PM

Description

Binding to observable property does not work in platform behaviors. Try any platform behavior community mvvm toolkit provides:

https://github.com/CommunityToolkit/Maui/tree/main/src/CommunityToolkit.Maui/Behaviors/PlatformBehaviors

or create your own, you would get the same result.

Here is an original stackoverflow thread https://stackoverflow.com/questions/74607699/binding-does-not-work-for-platform-dependent-behaviors

Steps to Reproduce

Take for example StatusBarBehavior, write something like

    <ContentPage.Behaviors>
        <toolkit:StatusBarBehavior StatusBarColor="{Binding StatusBarColorProp}" StatusBarStyle="LightContent" />
    </ContentPage.Behaviors>

create the property in your view model

    [ObservableProperty]
    private Color _statusBarColorProp;

Update the property value in code-behind or model like StatusBarColorProp=Color.FromRgb(255,0,0). You'll see status bar color does not change with StatusBarBehavior property change in runtime. Same for all the rest of behaviors. It works fine for non-bindings setters like StatusBarColor="Red".

Link to public reproduction project repository

https://github.com/CommunityToolkit/Maui/tree/main/src/CommunityToolkit.Maui/Behaviors/PlatformBehaviors

Version with bug

7.0 (current)

Last version that worked well

Unknown/Other

Affected platforms

I was not able test on other platforms

Affected platform versions

at least Android API 32 that I tested on, but does not seem to be platform dependent

Did you find any workaround?

interestingly while binding does not work for viewmodel, it does if you bind it to other control.

For example if you take BlurBehaviour from the repository https://github.com/VladislavAntonyuk/MauiSamples/tree/main/MauiImageEffects.

This code works fine:

<Image.Behaviors>
   <bh:BlurBehavior Radius="{Binding Value, Source={x:Reference imageBlurSlider}}"/>
</Image.Behaviors>

But this one does not

<Image.Behaviors>
   <bh:BlurBehavior Radius="{Binding MyMvvmBlurProperty}"/>
</Image.Behaviors>

Relevant log output

No response

[pictos]

I believe it's the default behavior, if I'm not wrong, since XF the bindingContext isn't passed to behavior automatically, if need to the BindingContext by your self, or use the {x:Reference} or RelativeToSource markup

[YMichurin]

if I see a control with a binding property, as its consumer I would expect binding to ViewModel work out of the box. Strange to hear that it's a default behavior, I feel something is definitely off here, either in implementation of community toolkit controls, or Maui core lib, or Maui design as a framework

[pictos]

@YMichurin it's been this way since XF. from docs

Important

.NET MAUI does not set the BindingContext of a behavior, because behaviors can be shared and applied to multiple controls through styles.

[pictos]

With that, I'll close this issue. Since it's this way by design