avalonia-data-binding

Avalonia Data Binding

Overview

(12.0+) compiled bindings are on by default (AvaloniaUseCompiledBindingsByDefault defaults true). {Binding} without x:DataType fails to compile. Compiled bindings are verified at build time and generate no reflection. Opt out per scope with x:CompileBindings="False", per binding with {ReflectionBinding}, or globally with <AvaloniaUseCompiledBindingsByDefault>false</AvaloniaUseCompiledBindingsByDefault>.

(11.x) compiled bindings are opt-in: set <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault> or x:CompileBindings="True"; otherwise {Binding} is reflection-based and {CompiledBinding} must be explicit.

Binding API in C# code

11.x	12.0+
IBinding	BindingBase (ReflectionBinding, CompiledBinding, TemplateBinding, IndexerBinding derive from it)
InstancedBinding	BindingExpressionBase
new Binding("Path")	new ReflectionBinding("Path") (Binding kept for compatibility = ReflectionBinding) or CompiledBinding

// (12.0+) typed compiled binding from a lambda
var b = CompiledBinding.Create((Item item) => item.Value);

Binding plugins (BindingPlugins) are removed in 12; data-annotations validation is off by default (11.x: on).

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Binding Modes

Mode	Direction	Updates
OneWay	Source → Target	On source change
TwoWay	Source ↔ Target	On either change
OneTime	Source → Target	Once at bind time
OneWayToSource	Target → Source	On target change
Default	Per-property default	Typically TwoWay for input controls, OneWay for display

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Basic Binding Syntax

<!-- Compiled binding — requires x:DataType on scope root -->
<Window xmlns:vm="using:MyApp.ViewModels"
        x:DataType="vm:MainViewModel">
    <TextBox Text="{Binding Name}"/>
    <TextBlock Text="{Binding Name, Mode=OneWay}"/>
    <TextBlock Text="{Binding Name, StringFormat='Hello, {0}!'}"/>
</Window>

<!-- Opt out per-binding (reflection binding) -->
<TextBox Text="{Binding Name, x:CompileBindings=False}"/>

<!-- Explicit compiled binding syntax (default in 12.0+; required in 11.x unless compiled-by-default is set) -->
<TextBox Text="{CompiledBinding Name}"/>