The error "Property Not Found" occurs when using x:DataType in a DataTemplate. about microsoft-ui-xaml

[kmgallahan]

Your sample project has 2 problems.

1. You are using x:DataType in a ResourceDictionary that does not have a code-behind file
2. You have a self-referential infinite loop of ContentTemplateSelector, as RootControl uses a selector that can select it

Getting rid of the infinite loop and doing this works:

<?xml version="1.0" encoding="utf-8" ?>
<Window
  x:Class="DockToy.MainWindow"
  xmlns:controls="using:DockToy.controls"
  xmlns:local="using:DockToy"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">

  <Page>
    <Page.Resources>
      <ResourceDictionary
        xmlns:local="using:DockToy"
        xmlns:models="using:DockToy.models"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">

        <DataTemplate x:Key="RootDockTemplate" x:DataType="models:IRoot">
          <local:RootControl Content="{x:Bind Content}" />
        </DataTemplate>

        <DataTemplate x:Key="DocumentDockTemplate" x:DataType="models:IDocument">
          <local:DocumentControl Content="{x:Bind Content}" />
        </DataTemplate>

        <local:DockTemplateSelector
          x:Key="DockControlSelector"
          DocumnentDockTemplate="{StaticResource DocumentDockTemplate}"
          RootDockTemplate="{StaticResource RootDockTemplate}" />
      </ResourceDictionary>
    </Page.Resources>
    <local:DockControl ContentTemplateSelector="{StaticResource DockControlSelector}">
      <controls:RootDock>
        <controls:DocumentDock>
          <TextBlock Text="I am a TextBlock" />
        </controls:DocumentDock>
      </controls:RootDock>
    </local:DockControl>
  </Page>
</Window>

Note that I used x:Bind here because as it has better performance, but Binding can be used if required.

Also note that a ContentControl, like UserControl, has special requirements on resource lookup:

https://learn.microsoft.com/en-us/windows/apps/design/style/xaml-resource-dictionary#usercontrol-usage-scope

[bpulliam]

Let us know if the suggestions don't work for you.

[github-actions]

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Please view the issues below to see if they solve your problem, and if the issue describes your problem please consider closing this one. Thank you!

Open similar issues:

• x:DataType doesn't work with nested types from other assemblies (#3238), similarity score: 0.73
• x:DataType="x:String" in DataTemplate of a ListView gives namespace issue (#6088), similarity score: 0.70

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• WinUI3 C++/WinRT - error when I create a DataTemplate Selector. (#7542), similarity score: 0.71

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[GochenRyan]

Thanks for the suggestion. While @kmgallahan recommendation is indeed effective, it doesn't align with the specific requirements I aim to address. In fact, I intend to create a WinUI Class Library, so ultimately, I won't have a Window.

Regarding the first problem, placing DataTemplates under ResourceDictionary is intended for inclusion in the MergedDictionaries section of app.xaml for sharing purposes. By setting ContentTemplateSelector on the subclass of ContentControl, for each Model object in the node tree Dock-RootDock-DocumentDock, DockControlSelector helps it find the corresponding control.

As for the second problem, to be honest, I haven't quite grasped it. Could you please provide further clarification on how I can replicate it? I've attempted to by placing breakpoints in SelectTemplateCore, but I haven't observed an infinite loop.

[GochenRyan]

<local:DockControl ContentTemplateSelector="{StaticResource DockControlSelector}">
    <controls:RootDock>
        <controls:DocumentDock>
            <TextBlock Text="I am a TextBlock" />
        </controls:DocumentDock>
    </controls:RootDock>
</local:DockControl>

If I write it this way, I can only set the control corresponding to RootDock, and subsequent child nodes cannot be processed.

[kmgallahan]

Here in RootControl you state you want DockControlSelector to be used to choose its content:

https://github.com/GochenRyan/WinUISample/blob/ba02c9cdbe365f69fb57f7b4d382ab724a205ae6/WinUISample/DockToy/RootControl.xaml#L10

And here DockControlSelector states it can pick RootControl to be the content:

https://github.com/GochenRyan/WinUISample/blob/ba02c9cdbe365f69fb57f7b4d382ab724a205ae6/WinUISample/DockToy/DockTemplate.xaml#L26

[GochenRyan]

Maybe I should create a new control to apply the selector to all nodes in its content