Binding resolution for TemplateBinding fails when value provided by upper Binding #33984
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I have a custom control Collection xaml <CollectionView ItemsSource="{Binding Source={x:Reference ThisPage}, Path=Categories}">
<CollectionView.ItemTemplate>
<DataTemplate x:DataType="models:ItemCategory">
<controls:Collapser
Label="{Binding Name}"> <!-- THIS CAUSES EXCEPTION -->
...
</controls:Collapser>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>Collapser xaml <ContentView xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:controls="clr-namespace:....Controls"
x:Class="ToolerMobile.Controls.Collapser">
<ContentView.Resources>
<ControlTemplate x:Key="CollapserControlTemplate">
<VerticalStackLayout>
<HorizontalStackLayout>
<Label
Text="{TemplateBinding Label}"/>
</HorizontalStackLayout>
<ContentPresenter/>
</VerticalStackLayout>
</ControlTemplate>
<Style TargetType="controls:Collapser">
<Setter Property="ControlTemplate" Value="{StaticResource CollapserControlTemplate}"/>
</Style>
</ContentView.Resources>
</ContentView>ItemCategory cs public class ItemCategory: ObservableObject
{
public string Id { get; set; }
public string Name { get; set; }
public ItemCategory[]? Subcategories { get; set; }
}Exception stack |
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Replies: 2 comments 6 replies
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I would name your property Collapser.LabelText instead of Collapser.Label. Also, I would implement it using C#, no need for XAML: using CommunityToolkit.Maui;
using CommunityToolkit.Maui.Markup;
public partial class Collapser : ContentView
{
[BindableProperty]
public partial string LabelText { get; set; } = string.Empty;
public Collapser()
{
ControlTemplate = new ControlTemplate(
() => new VerticalStackLayout
{
new HorizontalStackLayout { new Label().Bind(Label.TextProperty, (Collapser c) => c.LabelText, source: this) },
new ContentPresenter()
});
}
} |
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Well aside from "I would"s, does this actually fix the issue I was explaining? Preference between C# impl vs XAML isn't really what I am looking to solve here. |
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It’s hard to determine exactly what’s happening in your example. Including more code – especially the C# side of your In general, <VerticalStackLayout>
<HorizontalStackLayout
BindingContext="{Binding x:DataType='controls:Collapser', Source={RelativeSource TemplatedParent}"
x:DataType="controls:Collapser">
<Label Text="{Binding Label}"/>
</HorizontalStackLayout>
<ContentPresenter/>
</VerticalStackLayout> |
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Well even doing it with pure C# doesn't fix the problem as it still produces the same stack trace. Using just C# to declare isnt that much more straight forward. This view is very simple so even the C# side of it shouldnt be an issue public partial class Collapser: ContentView
{
private static readonly BindableProperty LabelProperty = BindableProperty.Create(nameof(Label), typeof(string), typeof(Collapser), "");
public Collapser()
{
InitializeComponent();
}
public string Label
{
get => (string)GetValue(LabelTextProperty);
set => SetValue(LabelTextProperty, value);
}
} |
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Your stack trace references code you haven’t provided, and without that missing context the issue can’t be reproduced. Using only the code you shared, I was able to build an application that runs without crashing, so the problem is likely in the parts you haven’t included. |
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Well unfortunately there is nothing else. All the code that affects this issue is already included. The rest of the stack trace that I did not provided does not reference my code and only Maui or Java.Interop. There is a difference between your test and my code in that I don't use Community attributes. Did you try it using the explicit BindableProperty way? |
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Feel free to fork and edit my code or create your own minimal reproducible example. |
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So turns out changing the BindableProperty to public instead of private fixed the issue. 🤦🏽♂️ |
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So turns out changing the BindableProperty to public instead of private fixed the issue. 🤦🏽♂️