Improve Compiled Bindings + Context

[wieslawsoltes]

PR Summary: Issue 973 – Compiled Bindings + Context

Overview

This PR addresses the compiled binding errors reported in issue 973 by documenting the correct binding pattern and updating the ItemsSource sample to be compiled-binding-safe. It also adds [DataType] metadata to template-like classes (DocumentTemplate, Document, Tool) to align with Avalonia’s DataTemplate conventions for better design-time inference.

Changes Included

Documentation

• Added a concise "compiled bindings + Context" note in dock-itemssource.md with a working pattern that rebases bindings onto the model via a nested DataContext.
• Added a troubleshooting entry in dock-content-guide.md for compiled binding errors involving Context.*, explaining the cause and the recommended fix pattern.

Sample Update

• Updated samples/DockXamlSample/ItemsSourceExample.axaml to:
  • Explicitly set x:DataType="dock:Document" on the template root.
  • Move x:DataType="local:MyDocumentModel" to a nested child under DataContext="{Binding Context}".
  • Bind model properties (Content, EditableContent, Status) under the nested model-typed subtree.

Metadata Improvements

Added [DataType] attributes to the following properties to enable Avalonia’s x:DataType inference and compiled binding metadata mapping:

• Dock.Model.Avalonia.Controls.DocumentTemplate.DataType
• Dock.Model.Avalonia.Controls.Document.DataType
• Dock.Model.Avalonia.Controls.Tool.DataType

Why This Works

DocumentTemplate uses Document as its data context. Document.Context is typed object?, so compiled bindings can’t resolve Context.SomeProperty directly. The nested DataContext="{Binding Context}" pattern provides a strongly-typed subtree for compiled bindings. Adding [DataType] to template-like types aligns with Avalonia’s conventions and improves design-time and compile-time metadata resolution.

Usage Guidance

When using ItemsSource + DocumentTemplate with compiled bindings:

<DocumentTemplate>
  <StackPanel x:DataType="dock:Document">
    <TextBox Text="{Binding Title}" />
    <StackPanel DataContext="{Binding Context}">
      <StackPanel x:DataType="local:MyDocumentModel">
        <TextBox Text="{Binding Content}" />
      </StackPanel>
    </StackPanel>
  </StackPanel>
</DocumentTemplate>

This avoids compile-time errors like:

• "Unable to resolve property 'Title' in data context of type 'ItemsSourceExampleViewModel'"
• "Unable to resolve property 'Context' in data context of type 'MyDocumentModel'"

Files Touched

• docfx/articles/dock-itemssource.md
• docfx/articles/dock-content-guide.md
• samples/DockXamlSample/ItemsSourceExample.axaml
• src/Dock.Model.Avalonia/Controls/DocumentTemplate.cs
• src/Dock.Model.Avalonia/Controls/Document.cs
• src/Dock.Model.Avalonia/Controls/Tool.cs

Notes

These changes do not alter runtime behavior of Context binding; they document and formalize the correct compiled-binding pattern and improve metadata for tooling and compile-time validation.

Fixes #973