Andy (Steve) De George
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title, ms.date, dev_langs, helpviewer_keywords, ms.assetid
| title | ms.date | dev_langs | helpviewer_keywords | ms.assetid | |||||
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| Optimizing Performance: Layout and Design | 03/30/2017 |
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Optimizing Performance: Layout and Design
The design of your WPF application can impact its performance by creating unnecessary overhead in calculating layout and validating object references. The construction of objects, particularly at run time, can affect the performance characteristics of your application.
This topic provides performance recommendations in these areas.
Layout
The term "layout pass" describes the process of measuring and arranging the members of a xref:System.Windows.Controls.Panel-derived object's collection of children, and then drawing them onscreen. The layout pass is a mathematically-intensive process—the larger the number of children in the collection, the greater the number of calculations required. For example, each time a child xref:System.Windows.UIElement object in the collection changes its position, it has the potential to trigger a new pass by the layout system. Because of the close relationship between object characteristics and layout behavior, it's important to understand the type of events that can invoke the layout system. Your application will perform better by reducing as much as possible any unnecessary invocations of the layout pass.
The layout system completes two passes for each child member in a collection: a measure pass, and an arrange pass. Each child object provides its own overridden implementation of the xref:System.Windows.UIElement.Measure%2A and xref:System.Windows.UIElement.Arrange%2A methods in order to provide its own specific layout behavior. At its simplest, layout is a recursive system that leads to an element being sized, positioned, and drawn onscreen.
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A child xref:System.Windows.UIElement object begins the layout process by first having its core properties measured.
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The object's xref:System.Windows.FrameworkElement properties that are related to size, such as xref:System.Windows.FrameworkElement.Width%2A, xref:System.Windows.FrameworkElement.Height%2A, and xref:System.Windows.FrameworkElement.Margin%2A, are evaluated.
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xref:System.Windows.Controls.Panel-specific logic is applied, such as the xref:System.Windows.Controls.DockPanel.Dock%2A property of the xref:System.Windows.Controls.DockPanel, or the xref:System.Windows.Controls.StackPanel.Orientation%2A property of the xref:System.Windows.Controls.StackPanel.
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Content is arranged, or positioned, after all child objects have been measured.
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The collection of child objects is drawn to the screen.
The layout pass process is invoked again if any of the following actions occur:
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A child object is added to the collection.
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A xref:System.Windows.FrameworkElement.LayoutTransform%2A is applied to the child object.
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The xref:System.Windows.UIElement.UpdateLayout%2A method is called for the child object.
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When a change occurs to the value of a dependency property that is marked with metadata affecting the measure or arrange passes.
Use the Most Efficient Panel where Possible
The complexity of the layout process is directly based on the layout behavior of the xref:System.Windows.Controls.Panel-derived elements you use. For example, a xref:System.Windows.Controls.Grid or xref:System.Windows.Controls.StackPanel control provides much more functionality than a xref:System.Windows.Controls.Canvas control. The price for this greater increase in functionality is a greater increase in performance costs. However, if you do not require the functionality that a xref:System.Windows.Controls.Grid control provides, you should use the less costly alternatives, such as a xref:System.Windows.Controls.Canvas or a custom panel.
For more information, see Panels Overview.
Update Rather than Replace a RenderTransform
You may be able to update a xref:System.Windows.Media.Transform rather than replacing it as the value of a xref:System.Windows.UIElement.RenderTransform%2A property. This is particularly true in scenarios that involve animation. By updating an existing xref:System.Windows.Media.Transform, you avoid initiating an unnecessary layout calculation.
Build Your Tree Top-Down
When a node is added or removed from the logical tree, property invalidations are raised on the node's parent and all its children. As a result, a top-down construction pattern should always be followed to avoid the cost of unnecessary invalidations on nodes that have already been validated. The following table shows the difference in execution speed between building a tree top-down versus bottom-up, where the tree is 150 levels deep with a single xref:System.Windows.Controls.TextBlock and xref:System.Windows.Controls.DockPanel at each level.
| Action | Tree building (in ms) | Render—includes tree building (in ms) |
|---|---|---|
| Bottom-up | 366 | 454 |
| Top-down | 11 | 96 |
The following code example demonstrates how to create a tree top down.
[!code-csharpPerformance#PerformanceSnippet1] [!code-vbPerformance#PerformanceSnippet1]
For more information on the logical tree, see Trees in WPF.