What's new in XAML of .NET 4.0

Easy Object References with {x:Reference}
Built-in Types
Generics in XAML with x:TypeArguments
Support for Arbitrary Dictionary Keys
Use of Non-Default Constructors with x:Arguments
Use of Static Factory Methods with x:FactoryMethod


With .NET 4.0 Microsoft will bring up a improved version of XAML. This arcitle shows you the language enhancements they made.

Easy Object References with {x:Reference}

If you want to create an object reference today you need to do a databinding and declare the source with an ElementName. In XAML 2009 you can use the new {x:Reference} markup extension

 
<!-- XAML 2006 -->
<Label Target="{Binding ElementName=firstName}">FirstName</Label>
<TextBox x:Name="firstName" />
 
<!-- XAML 2009 -->
<Label Target="{x:Reference firstName}">FirstName</Label>
<TextBox x:Name="firstName" />
 
 

Built-in Types

If you want to add objects of simple types like string or double to a resource dictionary today you need to map the needed clr-namespaces to an XML namespaces. In XAML 2009 we a lot of simple types that are included in the XAML language.

 
<!-- XAML 2006 -->
<sys:String xmlns:sys="clr-namespace:System;assembly=mscorlib >Test</sys:String>
 
<!-- XAML 2009 -->
<x:String>Test</x:String>
 
 

The following types are included into the XAML language:

• <x:Object/>
• <x:Boolean/>
• <x:Char/>
• <x:String/>
• <x:Decimal/>
• <x:Single/>
• <x:Double/>
• <x:Int16/>
• <x:Int32/>
• <x:Int64/>
• <x:TimeSpan/>
• <x:Uri/>
• <x:Byte/>
• <x:Array/>
• <x:List/>
• <x:Dictionary/>

Generics in XAML with x:TypeArguments

If you want to use an ObservableCollection<Employee> in XAML you need to create a type that derives from ObservableCollection because you cannot declare it in XAML. With XAML 2009 you can use the x:TypeArguments attribute to define the type of a generic type.

 
<!-- XAML 2006 -->
class EmployeeCollection : ObservableCollection<Employee>
{
}
 
<l:EmployeeCollection>
    <l:Employee FirstName="John" Name="Doe" />
    <l:Employee FirstName="Tim" Name="Smith" />
</lEmployeeCollection>
 
<!-- XAML 2009 -->
<ObservableCollection x:TypeArguments="Employee">
    <l:Employee FirstName="John" Name="Doe" />
    <l:Employee FirstName="Tim" Name="Smith" />
</ObservableCollection />
 
 

Support for Arbitrary Dictionary Keys

In XAML 2006 all explicit x:Key value were threated as strings. In XAML 2009 you can define any type of key you like by writing the key in ElementSyntax.

 
<!-- XAML 2006 -->
<StreamGeometry x:Key="CheckGeometry">M 0 0 L 12 8 l 9 12 z</StreamGeometry>
 
<!-- XAML 2009 -->
<StreamGeometry>M 0 0 L 12 8 l 9 12 z
    <x:Key><x:Double>10.0</x:Double></x:Key>
</StreamGeometry>
 
 

Use of Non-Default Constructors with x:Arguments

In XAML 2006 objects must have a public default constructor to use them. In XAML 2009 you can pass constructor arguments by using the x:Arguments syntax.

 
<!-- XAML 2006 -->
<DateTime>00:00:00.0000100</DateTime>
 
<!-- XAML 2009 -->
<DateTime>
    <x:Arguments>
        <x:Int64>100</x:Int64>
    </x:Arguments>
</DateTime>
 
 

Use of Static Factory Methods with x:FactoryMethod

When you have a type that has no public constructor but a static factory method you had to create that type in code in XAML 2006. With XAML 2009 you can use the x:FactoryMethodx:Arguments attribute to pass the argument values.

 
<!-- XAML 2006 -->
Guid id = Guid.NewGuid();
 
<!-- XAML 2009 -->
<Guid x:FactoryMethod="Guid.NewGuid" />