Template Selectors

Template selectors (i.e., DataTemplateSelector) are primarily used with a ContentPresenter to automatically select the best DataTemplate for the current Content.

ImageTemplateSelector Overview

The ImageTemplateSelector can be used to define an image from multiple sources. The following DataTemplate properties are supported:

Property	Description
DefaultTemplate	Defines the template to be used for `null` data values. This property is typically undefined but can be populated to insert a placeholder for undefined image data instead of leaving it empty.
GeometryTemplate	Defines the template to be used with `Geometry` data values. This is typically a `Path` filled with the `TextElement.Foreground` brush.
ImageSourceTemplate	Defines the template to be used with `ImageSource` data values. This is typically a DynamicImage control.

Some controls will have their image properties based on the object data type instead of ImageSource. For those controls, the corresponding control template will use a ContentPresenter with the image property as Content and assign a default instance of ImageTemplateSelector for the ContentTemplateSelector.

The following example demonstrates creating an instance of ImageTemplateSelector using templates that are consistent with typical usage scenarios:

xmlns:shared="http://schemas.actiprosoftware.com/winfx/xaml/shared"
...

<shared:ImageTemplateSelector x:Key="ImageTemplateSelector">

	<shared:ImageTemplateSelector.GeometryTemplate>
		<DataTemplate>
			<Viewbox>
				<Path Fill="{Binding Path=(TextElement.Foreground), RelativeSource={RelativeSource Mode=Self}}" Data="{Binding}" />
			</Viewbox>
		</DataTemplate>
	</shared:ImageTemplateSelector.GeometryTemplate>

	<shared:ImageTemplateSelector.ImageSourceTemplate>
		<DataTemplate>
			<shared:DynamicImage Source="{Binding}" />
		</DataTemplate>
	</shared:ImageTemplateSelector.ImageSourceTemplate>

</shared:ImageTemplateSelector>

The following data values are recognized by the ImageTemplateSelector:

Content	Description
`Geometry`	`Geometry` values (i.e. path data) will use GeometryTemplate
`ImageSource`	`ImageSource` values will use ImageSourceTemplate
`null`	`null` values will use DefaultTemplate.
`string`	`string` values will be analyzed to determine the type of data represented by the `string` and use the most appropriate template. See the "String Value Processing" section below for more details.
`Uri`	`Uri` values will use ImageSourceTemplate.

Note

Non-null data values will return a null reference as the DataTemplate that allows the ContentPresenter to use default logic for presenting the data .

String Value Processing

A string value is analyzed to determine the type of data represented so the best template can be used.

Any string that starts with "/" or "pack::" is assumed to be a Uri for an ImageSource and will use ImageSourceTemplate. Set the AllowStringUri instance property to false to prevent processing a string value as a Uri. The DefaultAllowStringUri static property can be set to false to disable Uri processing for all new class instances.

Any string that can be parsed by Geometry.Parse without throwing an exception will use GeometryTemplate. Set the AllowStringGeometry instance property to false to prevent processing a string value as a Geometry. The DefaultAllowStringGeometry static property can be set to false to disable Geometry processing for all new class instances.

Important

When AllowStringGeometry is true, a FormatException can be thrown when attempting to parse the string. This exception is handled but may appear in the Output window of debuggers like Visual Studio. If Geometry strings are not used by an application, set the DefaultAllowStringGeometry static property to false to prevent exceptions from failed parse attempts.

The following demonstrates several common ways to define a custom icon for the InfoBar control which utilizes ImageTemplateSelector:

xmlns:shared="http://schemas.actiprosoftware.com/winfx/xaml/shared"
...

<!-- String URI will use ImageSourceTemplate -->
<shared:InfoBar ... Icon="/Images/Icons/Help16.png" />

<!-- String Geometry will use GeometryTemplate -->
<shared:InfoBar ... Icon="M 0,0 L 10,10 M 0,10 L 10,0" />

<!-- Any unrecognized non-null data type is used directly -->
<shared:InfoBar ... >
	<shared:InfoBar.Icon>
		<Border BorderThickness="1" BorderBrush="Black">
			<Image Source="/Images/Icons/Help16.png" />
		</Border>
	</shared:InfoBar.Icon>
</shared:InfoBar>

In This Article

Template Selectors

ImageTemplateSelector Overview

Note

String Value Processing

Important