Otimização de desempenho: Recursos do aplicativo

Artigo
08/04/2011

WPF allows you to share application resources so that you can support a consistent look or behavior across similar-typed elements. This topic provides a few recommendations in this area that can help you improve the performance of your applications.

For more information on resources, see Visão geral sobre Recursos.

If your application uses custom controls and defines resources in a ResourceDictionary (or XAML Resources node), it is recommended that you either define the resources at the Application or Window object level, or define them in the default theme for the custom controls. Defining resources in a custom control's ResourceDictionary imposes a performance impact for every instance of that control. For example, if you have performance-intensive brush operations defined as part of the resource definition of a custom control and many instances of the custom control, the application's working set will increase significantly.

To illustrate this point, consider the following. Let's say you are developing a card game using WPF. For most card games, you need 52 cards with 52 different faces. You decide to implement a card custom control and you define 52 brushes (each representing a card face) in the resources of your card custom control. In your main application, you initially create 52 instances of this card custom control. Each instance of the card custom control generates 52 instances of Brush objects, which gives you a total of 52 * 52 Brush objects in your application. By moving the brushes out of the card custom control resources to the Application or Window object level, or defining them in the default theme for the custom control, you reduce the working set of the application, since you are now sharing the 52 brushes among 52 instances of the card control.

If you have multiple elements using the same Brush object, define the brush as a resource and reference it, rather than defining the brush inline in XAML. This method will create one instance and reuse it, whereas defining brushes inline in XAML creates a new instance for each element.

The following markup sample illustrates this point:

<StackPanel.Resources>
  <LinearGradientBrush x:Key="myBrush" StartPoint="0,0.5" EndPoint="1,0.5" Opacity="0.5">
    <LinearGradientBrush.GradientStops>
      <GradientStopCollection>
        <GradientStop Color="GoldenRod" Offset="0" />
        <GradientStop Color="White" Offset="1" />
      </GradientStopCollection>
    </LinearGradientBrush.GradientStops>
  </LinearGradientBrush>
</StackPanel.Resources>

<!-- Non-shared Brush object. -->
<Label>
  Label 1
  <Label.Background>
    <LinearGradientBrush StartPoint="0,0.5" EndPoint="1,0.5" Opacity="0.5">
      <LinearGradientBrush.GradientStops>
        <GradientStopCollection>
          <GradientStop Color="GoldenRod" Offset="0" />
          <GradientStop Color="White" Offset="1" />
        </GradientStopCollection>
      </LinearGradientBrush.GradientStops>
    </LinearGradientBrush>
  </Label.Background>
</Label>

<!-- Shared Brush object. -->
<Label Background="{StaticResource myBrush}">Label 2</Label>
<Label Background="{StaticResource myBrush}">Label 3</Label>

Use Static Resources when Possible

A static resource provides a value for any XAML property attribute by looking up a reference to an already defined resource. Lookup behavior for that resource is analogous to compile-time lookup.

A dynamic resource, on the other hand, will create a temporary expression during the initial compilation and thus defer lookup for resources until the requested resource value is actually required in order to construct an object. Lookup behavior for that resource is analogous to run-time lookup, which imposes a performance impact. Use static resources whenever possible in your application, using dynamic resources only when necessary.

The following markup sample shows the use of both types of resources:

<StackPanel.Resources>
  <SolidColorBrush x:Key="myBrush" Color="Teal"/>
</StackPanel.Resources>

<!-- StaticResource reference -->
<Label Foreground="{StaticResource myBrush}">Label 1</Label>

<!-- DynamicResource reference -->
<Label Foreground="{DynamicResource {x:Static SystemColors.ControlBrushKey}}">Label 2</Label>