Resources in WPF and difference between Static Resource and Dynamic Resource

In WPF, Resources  are objects which can be reused anywhere in a WPF application. For example styles, brushes, Bitmap images etc. can be used as resources in different places in your WPF application.

Here’s a list of place where your resources can be declared:

• As global application scope within the application App.xaml file
• As Window level scope within the Resources property of the current Window
• Within the Resources property of any FrameworkElement or FrameworkContentElement.
• Separate XAML resource file.

  Here’s a diagrammatic representation of the places where resources can be declared:

As seen here, WPF resources can be declared at application level in the App.xaml file. You can also declare WPF Resources at Window/User Control level or declare them at panel level.

In case your resources are growing, then you can declare them in a separate file called as Resource Dictionary which you can refer at application level or any other level which you want to.

Let's see some examples of declaring resources at various levels -

Application Level Resources -

<Application.Resources>
    <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" x:Key="myBackgroundColor">
        <GradientStop Offset="0" Color="Blue"/>
        <GradientStop Offset="0.4" Color="Red"/>
        <GradientStop Offset="0.7" Color="Purple"/>
        <GradientStop Offset="1" Color="Yellow"/>
    </LinearGradientBrush>
</Application.Resources>

Window Level Resources -

<Window.Resources>
    <SolidColorBrush x:Key="textForeColorResource" Color="Blue"/>
</Window.Resources>

Panel Level Resources -

<Grid.Resources>
    <BitmapImage x:Key="bitmapImageResource" UriSource="Koala.jpg" Rotation="Rotate90"/>
    <clrType:String x:Key="titleResource">WelCome To www.dotnetcurry.com</clrType:String>
</Grid.Resources>

Please note that <clrType:String/> is coming from the imported namespace "System" -

xmlns:clrType="clr-namespace:System;assembly=mscorlib"

Utilizing WPF Resources

Let's see how to utilize these resources in our WPF Application. Resources declared in WPF application can be utilized in two different ways -

1. Static Resource - Static resources are the resources which you cannot manipulate at runtime. The static resources are evaluated only once by the element which refers them during the loading of XAML.

2. Dynamic Resource - Dynamic resources are the resources which you can manipulate at runtime and are evaluated at runtime. If your code behind changes the resource, the elements referring resources as dynamic resources will also change.

For example, if you use "bitmapImageResource" as a static resource, it will not change even if you manipulate the images source at runtime.

However let us say, if you are referring "textForeColorResource" as a dynamic resource and if your code behind logic changes the color at runtime, the elements which are referring this resource will get affected.

Note: Using Static Resources improves the performance of your WPF application. When you are using Dynamic Resources, make sure that the Element Properties must be Dependency Property. This behavior is because, DPs have Change Notification support implicitly implemented, which in turn updates your UI.

Let's see how to use these resources and change them at runtime -

<Window x:Class="WPFResources.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"
        xmlns:clrType="clr-namespace:System;assembly=mscorlib"
        >
    <Window.Resources>
        <SolidColorBrush x:Key="textForeColorResource" Color="Blue"/>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Grid.Resources>
            <BitmapImage x:Key="bitmapImageResource" UriSource="Koala.jpg" Rotation="Rotate90"/>
            <clrType:String x:Key="titleResource">WelCome To www.dotnetcurry.com</clrType:String>
        </Grid.Resources>
        <StackPanel Orientation="Horizontal" Grid.Row="0">
            <Image Name="firstImage" Source="{StaticResource ResourceKey=bitmapImageResource}" Height="100" Width="100" Stretch="Fill"/>
        </StackPanel>
        <TextBlock Text="WelCome" FontSize="18" Grid.Row="1" Foreground="{DynamicResource ResourceKey=textForeColorResource}"/>
        <Button Height="50" Width="200" Background="{StaticResource ResourceKey=myBackgroundColor}" Content="{StaticResource ResourceKey=titleResource}" Name="clickMe" Click="clickMe_Click"/>
    </Grid>
</Window>

Now let's write the following code which will change our SolidColorBrush to Red color on a button click event.

private void clickMe_Click(object sender, RoutedEventArgs e)
{
    SolidColorBrush findSolidColorBrush= this.FindResource("textForeColorResource") as SolidColorBrush;
    findSolidColorBrush.Color=Colors.Red;
    this.Resources.Remove("textForeColorResource");
    this.Resources.Add("textForeColorResource", findSolidColorBrush);
}

The output will look like the following-

Declare and refer resources in Resource Dictionary

To add a Resource Dictionary into your WPF application, right click the WPF project > add a Resource Dictionary.

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <LinearGradientBrush StartPoint="0,0" EndPoint="1,1" x:Key="myAnotherBackgroundColor">
        <GradientStop Offset="0" Color="Green"/>
        <GradientStop Offset="0.4" Color="PeachPuff"/>
        <GradientStop Offset="0.7" Color="Pink"/>
        <GradientStop Offset="1" Color="Silver"/>
    </LinearGradientBrush>
</ResourceDictionary>

Once you declare the resource dictionary, you can refer them at application level as shown below -

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="MyResourcesDictionary.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

Now apply the resource "myAnotherBackgroundColor" to button background and observe the changes.

This article has been editorially reviewed by Suprotim Agarwal.

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