How to Use Resources in WPF

This article will show how to use resources in WPF.

There are two types of resources; they are:

1. Static Resources
2. Dynamic Resources

Static Resources: A Static Resource will be resolved and assigned to the property during the loading of the XAML that occurs before the application is actually run. It will only be assigned once and any changes to the resource dictionary is ignored.

Static resource references work best for the following circumstances:

• Your application design concentrates most of its resources into page or application level resource dictionaries. Static resource references are not re-evaluated based on runtime behaviours such as reloading a page, and therefore there can be some performance benefit to avoiding large numbers of dynamic resource references when they are not necessary per your resource and application design.
• You are setting the value of a property that is not on a Dependency Object or a freezable.
• You are creating a resource dictionary that will be compiled into a DLL, and packaged as part of the application or shared between applications.
• You are creating a theme for a custom control, and are defining resources that are used within the themes. For this case, you typically do not want the dynamic resource reference lookup behaviour; you instead want the static resource reference behaviour so that the lookup is predictable and self-contained in the theme. With a dynamic resource reference, even a reference within a theme is left unevaluated until runtime, and there is a chance that when the theme is applied, some local element will redefine a key that your theme is trying to reference, and the local element will fall prior to the theme itself in the lookup. If that happens then your theme will not behave in an expected manner.
• You are using resources to set large numbers of dependency properties. Dependency properties have effective value caching as enabled by the property system, so if you provide a value for a dependency property that can be evaluated at load time then the dependency property does not need to check for a re-evaluated expression and can return the last effective value. This technique can be a performance benefit.
• You want to change the underlying resource for all consumers, or you want to maintain separate writable instances for each consumer using the x: Shared Attribute.

Example:

<Window.Resources>

        <SolidColorBrush x:Key="MyBrush" Color="Gold"/>

        <Style TargetType="Border" x:Key="PageBackground">

            <Setter Property="Background" Value="black"/>

        </Style>

        <Style TargetType="TextBlock" x:Key="TitleText">

            <Setter Property="Background" Value="Green"/>

            <Setter Property="DockPanel.Dock" Value="Top"/>

            <Setter Property="FontSize" Value="14"/>

            <Setter Property="Foreground" Value="#4E87D4"/>

            <Setter Property="FontFamily" Value="Tahoma"/>

            <Setter Property="Margin" Value="0,40,10,10"/>

            <Setter Property="Width" Value="300"></Setter>

        </Style>

        <Style TargetType="TextBlock" x:Key="Label">

            <Setter Property="DockPanel.Dock" Value="Right"/>

            <Setter Property="FontSize" Value="8"/>

            <Setter Property="Foreground" Value="{StaticResource MyBrush}"/>

            <Setter Property="FontFamily" Value="Arial"/>

            <Setter Property="FontWeight" Value="Bold"/>

            <Setter Property="Margin" Value="0,3,10,0"/>

            <Setter Property="Width" Value="100"></Setter>

            <Setter Property="Height" Value="20"></Setter>

        </Style>

</Window.Resources>

This is how we use a resource in controls:

<Grid>

        <StackPanel>

            <Border Style="{StaticResource PageBackground}">

                <DockPanel>

                    <TextBlock Style="{StaticResource TitleText}">Welcome to the static resource page</TextBlock>

                    <TextBlock Style="{StaticResource Label}">This is label text</TextBlock>

                    <TextBlock DockPanel.Dock="Top" HorizontalAlignment="Left" FontSize="20" Foreground="{StaticResource MyBrush}" Text="Hello Rajkumar Welcome !" Margin="20" />

                    <Button DockPanel.Dock="Top" HorizontalAlignment="Left" Height="30" Background="{StaticResource MyBrush}" Margin="40">Click To Enter :)</Button>

                    <Ellipse DockPanel.Dock="Top" HorizontalAlignment="Left" Width="100" Height="100" Fill="{StaticResource MyBrush}" />

                </DockPanel>

            </Border>

        </StackPanel>

</Grid>

Run the application and see the result like this:

 

Image 1.

Dynamic Resources: A Dynamic Resource assigns an Expression object to the property during loading but does not actually lookup the resource until runtime when the Expression object is asked for the value. This defers looking up the resource until it is needed at runtime. A good example would be a forward reference to a resource defined later on in the XAML. Another example is a resource that will not even exist until runtime. It will update the target if the source's resource dictionary is changed.

Dynamic resources work best for the following circumstances:

• The value of the resource depends on conditions that are not known until runtime. This includes system resources, or resources that are otherwise user settable. For example, you can create setter values that refer to system properties, as exposed by System Colours, System Fonts, or System Parameters. These values are truly dynamic because they ultimately come from the runtime environment of the user and operating system. You might also have application-level themes that can change, where page-level resource access must also capture the change.
• You are creating or referencing theme styles for a custom control.
• You intend to adjust the contents of a Resource Dictionary during an application lifetime.
• You have a complicated resource structure that has interdependencies, where a forward reference may be required. Static resource references do not support forward references, but dynamic resource references do support them because the resource does not need to be evaluated until runtime, and forward references are therefore not a relevant concept.
• You are referencing a resource that is particularly large from the perspective of a compile or working set, and the resource might not be used immediately when the page loads. Static resource references always load from XAML when the page loads; however, a dynamic resource reference does not load until it is actually used.
• You are creating a style where setter values might come from other values that are influenced by themes or other user settings.
• You are applying resources to elements that might be represented in the logical tree during application lifetime. Changing the parent also potentially changes the resource lookup scope, so if you want the resource for a represented element to be revaluated based on the new scope; always use a dynamic resource reference.

Example:

<Window.Resources>

        <SolidColorBrush x:Key="brush" Color="Green"  />

        <Style TargetType="Border" x:Key="PageBackground">

            <Setter Property="Background" Value="Gold"/>

        </Style>

</Window.Resources>

<Grid>

        <Border Style="{DynamicResource PageBackground}">

        <Button x:Name="btn" Content="Rajkumar Test" Click="Button_Click" Background="{DynamicResource brush}" Height="30" Margin="53,130,85,130" />

        </Border>

</Grid>

You can apply on code behind like this.

private void Button_Click(object sender, RoutedEventArgs e)

{

   this.btn.SetResourceReference(BackgroundProperty, "brush");

}

The output will be like this: