Markup extensions

Markup extensions are special expressions enclosed in curly braces {} that provide dynamic values in XAML. They extend what you can express beyond simple string literals.

Binding

Creates a data binding between a control property and a source property:

<TextBlock Text="{Binding UserName}" />

Common binding parameters

Parameter	Description
Path	The property path on the source object. This is the default parameter.
Mode	The binding direction: OneWay, TwoWay, OneTime, OneWayToSource, Default.
Converter	An IValueConverter that transforms the value.
ConverterParameter	A parameter passed to the converter.
StringFormat	A format string applied to the bound value.
FallbackValue	The value used when the binding fails.
TargetNullValue	The value used when the source value is null.
Source	An explicit source object (overrides DataContext).
ElementName	Binds to a named element in the same XAML scope.
RelativeSource	Binds to a relative element (e.g., TemplatedParent, Self).

<TextBlock Text="{Binding Price, StringFormat='Price: {0:C}'}" />
<TextBox Text="{Binding Name, Mode=TwoWay}" />
<TextBlock Text="{Binding Amount, Converter={StaticResource CurrencyConverter}}" />
<Image Source="{Binding ImageUrl, FallbackValue={x:Null}}" />

info

For a comprehensive guide to binding syntax, see Data Binding Syntax.

CompiledBinding

A compile-time validated binding. Functionally equivalent to {Binding} when x:CompileBindings="True" is set, but can be used explicitly:

<TextBlock Text="{CompiledBinding UserName}" />

Compiled bindings require an x:DataType to be set in scope. They provide compile-time checking of binding paths and better runtime performance.

ReflectionBinding

A reflection-based binding that bypasses compile-time validation. Use this when binding to dynamic or late-bound properties:

<TextBlock Text="{ReflectionBinding DynamicProperty}" />

StaticResource

Looks up a resource by key from the current element's resource chain, walking up through parent elements to Application.Resources. The lookup happens once at load time.

<TextBlock Foreground="{StaticResource PrimaryBrush}" />

If the resource is not found, an exception is thrown at runtime.

Resource lookup order

1. The current element's Resources dictionary.
2. Parent elements' Resources dictionaries, walking up the logical tree.
3. The Application.Resources dictionary.
4. Theme resources.

DynamicResource

Similar to StaticResource, but the value updates automatically if the resource changes at runtime (e.g., when switching themes):

<TextBlock Foreground="{DynamicResource SystemAccentColor}" />

Use DynamicResource for:

• Theme-dependent values (colors, brushes, sizes)
• Resources that change at runtime (e.g., user preferences)
• Resources defined in theme dictionaries

Use StaticResource for:

• Values that never change at runtime
• Performance-sensitive scenarios (static lookup is slightly faster)

TemplateBinding

A lightweight binding used inside ControlTemplate definitions that binds to a property of the templated parent control:

<ControlTemplate TargetType="Button">
    <Border Background="{TemplateBinding Background}"
            Padding="{TemplateBinding Padding}"
            CornerRadius="{TemplateBinding CornerRadius}">
        <ContentPresenter Content="{TemplateBinding Content}" />
    </Border>
</ControlTemplate>

TemplateBinding is equivalent to {Binding RelativeSource={RelativeSource TemplatedParent}} but more efficient.

info

TemplateBinding only supports OneWay mode. If you need TwoWay binding inside a template, use {Binding RelativeSource={RelativeSource TemplatedParent}} instead.

OnPlatform

Returns a different value depending on the current operating system:

<TextBlock FontSize="{OnPlatform Default=14, macOS=13, Android=16}" />

<Window Width="{OnPlatform 800, macOS=900}" />

Supported platform values: Default, Windows, macOS, Linux, Android, iOS, Browser.

For complex values, use nested syntax:

<TextBlock>
    <TextBlock.Margin>
        <OnPlatform>
            <On Options="Windows">8,4</On>
            <On Options="macOS">12,6</On>
            <On Options="Default">8,4</On>
        </OnPlatform>
    </TextBlock.Margin>
</TextBlock>

OnFormFactor

Returns a different value based on the device form factor:

<TextBlock FontSize="{OnFormFactor Default=14, Desktop=14, Mobile=18}" />

Supported values: Default, Desktop, Mobile.

RelativeSource

Specifies a binding source relative to the binding target's position in the visual or logical tree. Used within {Binding}:

<!-- Bind to self -->
<Border Tag="{Binding Width, RelativeSource={RelativeSource Self}}" />

<!-- Bind to templated parent -->
<TextBlock Text="{Binding Header, RelativeSource={RelativeSource TemplatedParent}}" />

<!-- Bind to an ancestor by type -->
<TextBlock Text="{Binding DataContext.Title,
    RelativeSource={RelativeSource FindAncestor, AncestorType=Window}}" />

Markup extension syntax rules

Basic syntax

Property="{ExtensionName}"
Property="{ExtensionName Value}"
Property="{ExtensionName Param1=Value1, Param2=Value2}"

Nesting

Markup extensions can be nested:

<TextBlock Text="{Binding Name, Converter={StaticResource UpperCaseConverter}}" />

Escaping

To set a property to a literal string that starts with {, use an empty set of braces:

<TextBlock Text="{}{This is literal text, not a markup extension}" />

See also

• XAML Reference: Overview of XAML syntax.
• x: Directives: XAML language directives.
• Data Binding Syntax: Comprehensive binding syntax reference.
• Compiled Bindings: Compile-time validated bindings.
• Markup Extensions (Data Binding): Binding-specific markup extension details.