| title | description | ms.date | dev_langs | helpviewer_keywords | ms.assetid | |||||
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Panels Overview |
Windows Presentation Foundation provides predefined Panel elements that control the rendering of elements. Learn how to construct custom Panel elements. |
03/30/2017 |
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f73644af-9941-4611-8754-6d4cef03fc44 |
xref:System.Windows.Controls.Panel elements are components that control the rendering of elements—their size and dimensions, their position, and the arrangement of their child content. The Windows Presentation Foundation (WPF) provides a number of predefined xref:System.Windows.Controls.Panel elements as well as the ability to construct custom xref:System.Windows.Controls.Panel elements.
This topic contains the following sections.
xref:System.Windows.Controls.Panel is the base class for all elements that provide layout support in Windows Presentation Foundation (WPF). Derived xref:System.Windows.Controls.Panel elements are used to position and arrange elements in Extensible Application Markup Language (XAML) and code.
The WPF includes a comprehensive suite of derived panel implementations that enable many complex layouts. These derived classes expose properties and methods that enable most standard user interface (UI) scenarios. Developers who are unable to find a child arrangement behavior that meets their needs can create new layouts by overriding the xref:System.Windows.FrameworkElement.ArrangeOverride%2A and xref:System.Windows.FrameworkElement.MeasureOverride%2A methods. For more information on custom layout behaviors, see Custom Panel Elements.
All xref:System.Windows.Controls.Panel elements support the base sizing and positioning properties defined by xref:System.Windows.FrameworkElement, including xref:System.Windows.FrameworkElement.Height%2A, xref:System.Windows.FrameworkElement.Width%2A, xref:System.Windows.FrameworkElement.HorizontalAlignment%2A, xref:System.Windows.FrameworkElement.VerticalAlignment%2A, xref:System.Windows.FrameworkElement.Margin%2A, and xref:System.Windows.FrameworkElement.LayoutTransform%2A. For additional information on positioning properties defined by xref:System.Windows.FrameworkElement, see Alignment, Margins, and Padding Overview.
xref:System.Windows.Controls.Panel exposes additional properties that are of critical importance in understanding and using layout. The xref:System.Windows.Controls.Panel.Background%2A property is used to fill the area between the boundaries of a derived panel element with a xref:System.Windows.Media.Brush. xref:System.Windows.Controls.Panel.Children%2A represents the child collection of elements that the xref:System.Windows.Controls.Panel is comprised of. xref:System.Windows.Controls.Panel.InternalChildren%2A represents the content of the xref:System.Windows.Controls.Panel.Children%2A collection plus those members generated by data binding. Both consist of a xref:System.Windows.Controls.UIElementCollection of child elements hosted within the parent xref:System.Windows.Controls.Panel.
Panel also exposes a xref:System.Windows.Controls.Panel.ZIndex%2A?displayProperty=nameWithType attached property that can be used to achieve layered order in a derived xref:System.Windows.Controls.Panel. Members of a panel's xref:System.Windows.Controls.Panel.Children%2A collection with a higher xref:System.Windows.Controls.Panel.ZIndex%2A?displayProperty=nameWithType value appear in front of those with a lower xref:System.Windows.Controls.Panel.ZIndex%2A?displayProperty=nameWithType value. This is particularly useful for panels such as xref:System.Windows.Controls.Canvas and xref:System.Windows.Controls.Grid which allow children to share the same coordinate space.
xref:System.Windows.Controls.Panel also defines the xref:System.Windows.Controls.Panel.OnRender%2A method, which can be used to override the default presentation behavior of a xref:System.Windows.Controls.Panel.
Derived panel elements make extensive use of attached properties. An attached property is a specialized form of dependency property that does not have the conventional common language runtime (CLR) property "wrapper". Attached properties have a specialized syntax in Extensible Application Markup Language (XAML), which can be seen in several of the examples that follow.
One purpose of an attached property is to allow child elements to store unique values of a property that is actually defined by a parent element. An application of this functionality is having child elements inform the parent how they wish to be presented in the user interface (UI), which is extremely useful for application layout. For more information, see Attached Properties Overview.
Many objects derive from xref:System.Windows.Controls.Panel, but not all of them are intended for use as root layout providers. There are six defined panel classes (xref:System.Windows.Controls.Canvas, xref:System.Windows.Controls.DockPanel, xref:System.Windows.Controls.Grid, xref:System.Windows.Controls.StackPanel, xref:System.Windows.Controls.VirtualizingStackPanel, and xref:System.Windows.Controls.WrapPanel) that are designed specifically for creating application UI.
Each panel element encapsulates its own special functionality, as seen in the following table.
| Element Name | UI Panel? | Description |
|---|---|---|
| xref:System.Windows.Controls.Canvas | Yes | Defines an area within which you can explicitly position child elements by coordinates relative to the xref:System.Windows.Controls.Canvas area. |
| xref:System.Windows.Controls.DockPanel | Yes | Defines an area within which you can arrange child elements either horizontally or vertically, relative to each other. |
| xref:System.Windows.Controls.Grid | Yes | Defines a flexible grid area consisting of columns and rows. Child elements of a xref:System.Windows.Controls.Grid can be positioned precisely using the xref:System.Windows.FrameworkElement.Margin%2A property. |
| xref:System.Windows.Controls.StackPanel | Yes | Arranges child elements into a single line that can be oriented horizontally or vertically. |
| xref:System.Windows.Controls.Primitives.TabPanel | No | Handles the layout of tab buttons in a xref:System.Windows.Controls.TabControl. |
| xref:System.Windows.Controls.Primitives.ToolBarOverflowPanel | No | Arranges content within a xref:System.Windows.Controls.ToolBar control. |
| xref:System.Windows.Controls.Primitives.UniformGrid | No | xref:System.Windows.Controls.Primitives.UniformGrid is used to arrange children in a grid with all equal cell sizes. |
| xref:System.Windows.Controls.VirtualizingPanel | No | Provides a base class for panels that can "virtualize" their children collection. |
| xref:System.Windows.Controls.VirtualizingStackPanel | Yes | Arranges and virtualizes content on a single line oriented horizontally or vertically. |
| xref:System.Windows.Controls.WrapPanel | Yes | xref:System.Windows.Controls.WrapPanel positions child elements in sequential position from left to right, breaking content to the next line at the edge of the containing box. Subsequent ordering happens sequentially from top to bottom or right to left, depending on the value of the xref:System.Windows.Controls.WrapPanel.Orientation%2A property. |
There are six panel classes available in WPF that are optimized to support UI scenarios: xref:System.Windows.Controls.Canvas, xref:System.Windows.Controls.DockPanel, xref:System.Windows.Controls.Grid, xref:System.Windows.Controls.StackPanel, xref:System.Windows.Controls.VirtualizingStackPanel, and xref:System.Windows.Controls.WrapPanel. These panel elements are easy to use, versatile, and extensible enough for most applications.
Each derived xref:System.Windows.Controls.Panel element treats sizing constraints differently. Understanding how a xref:System.Windows.Controls.Panel handles constraints in either the horizontal or vertical direction can make layout more predictable.
| Panel Name | x-Dimension | y-Dimension |
|---|---|---|
| xref:System.Windows.Controls.Canvas | Constrained to content | Constrained to content |
| xref:System.Windows.Controls.DockPanel | Constrained | Constrained |
| xref:System.Windows.Controls.StackPanel (Vertical Orientation) | Constrained | Constrained to content |
| xref:System.Windows.Controls.StackPanel (Horizontal Orientation) | Constrained to content | Constrained |
| xref:System.Windows.Controls.Grid | Constrained | Constrained, except in cases where xref:System.Windows.GridUnitType.Auto apply to rows and columns |
| xref:System.Windows.Controls.WrapPanel | Constrained to content | Constrained to content |
More detailed descriptions and usage examples of each of these elements can be found below.
The xref:System.Windows.Controls.Canvas element enables positioning of content according to absolute x- and y- coordinates. Elements can be drawn in a unique location; or, if elements occupy the same coordinates, the order in which they appear in markup determines the order in which the elements are drawn.
xref:System.Windows.Controls.Canvas provides the most flexible layout support of any xref:System.Windows.Controls.Panel. Height and Width properties are used to define the area of the canvas, and elements inside are assigned absolute coordinates relative to the area of the parent xref:System.Windows.Controls.Canvas. Four attached properties, xref:System.Windows.Controls.Canvas.Left%2A?displayProperty=nameWithType, xref:System.Windows.Controls.Canvas.Top%2A?displayProperty=nameWithType, xref:System.Windows.Controls.Canvas.Right%2A?displayProperty=nameWithType and xref:System.Windows.Controls.Canvas.Bottom%2A?displayProperty=nameWithType, allow fine control of object placement within a xref:System.Windows.Controls.Canvas, allowing the developer to position and arrange elements precisely on the screen.
xref:System.Windows.Controls.Canvas can position child elements at any position on the screen, even at coordinates that are outside of its own defined xref:System.Windows.FrameworkElement.Height%2A and xref:System.Windows.FrameworkElement.Width%2A. Furthermore, xref:System.Windows.Controls.Canvas is not affected by the size of its children. As a result, it is possible for a child element to overdraw other elements outside the bounding rectangle of the parent xref:System.Windows.Controls.Canvas. The default behavior of a xref:System.Windows.Controls.Canvas is to allow children to be drawn outside the bounds of the parent xref:System.Windows.Controls.Canvas. If this behavior is undesirable, the xref:System.Windows.UIElement.ClipToBounds%2A property can be set to true. This causes xref:System.Windows.Controls.Canvas to clip to its own size. xref:System.Windows.Controls.Canvas is the only layout element that allows children to be drawn outside its bounds.
This behavior is graphically illustrated in the Width Properties Comparison Sample.
A xref:System.Windows.Controls.Canvas can be instantiated simply by using Extensible Application Markup Language (XAML) or code. The following example demonstrates how to use xref:System.Windows.Controls.Canvas to absolutely position content. This code produces three 100-pixel squares. The first square is red, and its top-left (x, y) position is specified as (0, 0). The second square is green, and its top-left position is (100, 100), just below and to the right of the first square. The third square is blue, and its top-left position is (50, 50), thus encompassing the lower-right quadrant of the first square and the upper-left quadrant of the second. Because the third square is laid out last, it appears to be on top of the other two squares—that is, the overlapping portions assume the color of the third box.
[!code-csharpCanvasOvwSample#1] [!code-vbCanvasOvwSample#1] [!code-xamlCanvasOvwSample#1]
The compiled application yields a new UI that looks like this.
The xref:System.Windows.Controls.DockPanel element uses the xref:System.Windows.Controls.DockPanel.Dock%2A?displayProperty=nameWithType attached property as set in child content elements to position content along the edges of a container. When xref:System.Windows.Controls.DockPanel.Dock%2A?displayProperty=nameWithType is set to xref:System.Windows.Controls.Dock.Top or xref:System.Windows.Controls.Dock.Bottom, it positions child elements above or below each other. When xref:System.Windows.Controls.DockPanel.Dock%2A?displayProperty=nameWithType is set to xref:System.Windows.Controls.Dock.Left or xref:System.Windows.Controls.Dock.Right, it positions child elements to the left or right of each other. The xref:System.Windows.Controls.DockPanel.LastChildFill%2A property determines the position of the final element added as a child of a xref:System.Windows.Controls.DockPanel.
You can use xref:System.Windows.Controls.DockPanel to position a group of related controls, such as a set of buttons. Alternately, you can use it to create a "paned" UI, similar to that found in Microsoft Outlook.
If its xref:System.Windows.FrameworkElement.Height%2A and xref:System.Windows.FrameworkElement.Width%2A properties are not specified, xref:System.Windows.Controls.DockPanel sizes to its content. The size can increase or decrease to accommodate the size of its child elements. However, when these properties are specified and there is no longer room for the next specified child element, xref:System.Windows.Controls.DockPanel does not display that child element or subsequent child elements and does not measure subsequent child elements.
By default, the last child of a xref:System.Windows.Controls.DockPanel element will "fill" the remaining, unallocated space. If this behavior is not desired, set the xref:System.Windows.Controls.DockPanel.LastChildFill%2A property to false.
The following example demonstrates how to partition space using a xref:System.Windows.Controls.DockPanel. Five xref:System.Windows.Controls.Border elements are added as children of a parent xref:System.Windows.Controls.DockPanel. Each uses a different positioning property of a xref:System.Windows.Controls.DockPanel to partition space. The final element "fills" the remaining, unallocated space.
[!code-cppDockPanelOvwSample#1] [!code-csharpDockPanelOvwSample#1] [!code-vbDockPanelOvwSample#1] [!code-xamlDockPanelOvwSample#1]
The compiled application yields a new UI that looks like this.
The xref:System.Windows.Controls.Grid element merges the functionality of an absolute positioning and tabular data control. A xref:System.Windows.Controls.Grid enables you to easily position and style elements. xref:System.Windows.Controls.Grid allows you to define flexible row and column groupings, and even provides a mechanism to share sizing information between multiple xref:System.Windows.Controls.Grid elements.
xref:System.Windows.Documents.Table and xref:System.Windows.Controls.Grid share some common functionality, but each is best suited for different scenarios. A xref:System.Windows.Documents.Table is designed for use within flow content (see Flow Document Overview for more information on flow content). Grids are best used inside of forms (basically anywhere outside of flow content). Within a xref:System.Windows.Documents.FlowDocument, xref:System.Windows.Documents.Table supports flow content behaviors like pagination, column reflow, and content selection while a xref:System.Windows.Controls.Grid does not. A xref:System.Windows.Controls.Grid on the other hand is best used outside of a xref:System.Windows.Documents.FlowDocument for many reasons including xref:System.Windows.Controls.Grid adds elements based on a row and column index, xref:System.Windows.Documents.Table does not. The xref:System.Windows.Controls.Grid element allows layering of child content, allowing more than one element to exist within a single "cell." xref:System.Windows.Documents.Table does not support layering. Child elements of a xref:System.Windows.Controls.Grid can be absolutely positioned relative to the area of their "cell" boundaries. xref:System.Windows.Documents.Table does not support this feature. Finally, a xref:System.Windows.Controls.Grid is lighter weight than a xref:System.Windows.Documents.Table.
Columns and rows defined within a xref:System.Windows.Controls.Grid can take advantage of xref:System.Windows.GridUnitType.Star sizing in order to distribute remaining space proportionally. When xref:System.Windows.GridUnitType.Star is selected as the Height or Width of a row or column, that column or row receives a weighted proportion of remaining available space. This is in contrast to xref:System.Windows.GridUnitType.Auto, which will distribute space evenly based on the size of the content within a column or row. This value is expressed as * or 2* when using Extensible Application Markup Language (XAML). In the first case, the row or column would receive one times the available space, in the second case, two times, and so on. By combining this technique to proportionally distribute space with a xref:System.Windows.FrameworkElement.HorizontalAlignment%2A and xref:System.Windows.FrameworkElement.VerticalAlignment%2A value of Stretch it is possible to partition layout space by percentage of screen space. xref:System.Windows.Controls.Grid is the only layout panel that can distribute space in this manner.
The following example demonstrates how to build a UI similar to that found on the Run dialog available on the Windows Start menu.
[!code-csharpGridRunDialog#1] [!code-vbGridRunDialog#1]
The compiled application yields a new UI that looks like this.
A xref:System.Windows.Controls.StackPanel enables you to "stack" elements in an assigned direction. The default stack direction is vertical. The xref:System.Windows.Controls.StackPanel.Orientation%2A property can be used to control content flow.
Although xref:System.Windows.Controls.DockPanel can also "stack" child elements, xref:System.Windows.Controls.DockPanel and xref:System.Windows.Controls.StackPanel do not produce analogous results in some usage scenarios. For example, the order of child elements can affect their size in a xref:System.Windows.Controls.DockPanel but not in a xref:System.Windows.Controls.StackPanel. This is because xref:System.Windows.Controls.StackPanel measures in the direction of stacking at xref:System.Double.PositiveInfinity, whereas xref:System.Windows.Controls.DockPanel measures only the available size.
The following example demonstrates this key difference.
[!code-cppStackPanelOvw4#1] [!code-csharpStackPanelOvw4#1] [!code-vbStackPanelOvw4#1] [!code-xamlStackPanelOvw4#1]
The difference in rendering behavior can be seen in this image.
The following example demonstrates how to use a xref:System.Windows.Controls.StackPanel to create a set of vertically-positioned buttons. For horizontal positioning, set the xref:System.Windows.Controls.StackPanel.Orientation%2A property to xref:System.Windows.Controls.Orientation.Horizontal.
[!code-csharpStackPanel_ovw2#1] [!code-vbStackPanel_ovw2#1]
The compiled application yields a new UI that looks like this.
WPF also provides a variation of the xref:System.Windows.Controls.StackPanel element that automatically "virtualizes" data-bound child content. In this context, the word virtualize refers to a technique by which a subset of elements are generated from a larger number of data items based upon which items are visible on-screen. It is intensive, both in terms of memory and processor, to generate a large number of UI elements when only a few may be on the screen at a given time. xref:System.Windows.Controls.VirtualizingStackPanel (through functionality provided by xref:System.Windows.Controls.VirtualizingPanel) calculates visible items and works with the xref:System.Windows.Controls.ItemContainerGenerator from an xref:System.Windows.Controls.ItemsControl (such as xref:System.Windows.Controls.ListBox or xref:System.Windows.Controls.ListView) to only create elements for visible items.
The xref:System.Windows.Controls.VirtualizingStackPanel element is automatically set as the items host for controls such as the xref:System.Windows.Controls.ListBox. When hosting a data bound collection, content is automatically virtualized, as long as the content is within the bounds of a xref:System.Windows.Controls.ScrollViewer. This greatly improves performance when hosting many child items.
The following markup demonstrates how to use a xref:System.Windows.Controls.VirtualizingStackPanel as an items host. The xref:System.Windows.Controls.VirtualizingStackPanel.IsVirtualizingProperty?displayProperty=nameWithType attached property must be set to true (default) for virtualization to occur.
[!code-xamlVirtualizingStackPanel_Intro#1]
xref:System.Windows.Controls.WrapPanel is used to position child elements in sequential position from left to right, breaking content to the next line when it reaches the edge of its parent container. Content can be oriented horizontally or vertically. xref:System.Windows.Controls.WrapPanel is useful for simple flowing user interface (UI) scenarios. It can also be used to apply uniform sizing to all of its child elements.
The following example demonstrates how to create a xref:System.Windows.Controls.WrapPanel to display xref:System.Windows.Controls.Button controls that wrap when they reach the edge of their container.
[!code-cppWrapPanel_Intro#1] [!code-csharpWrapPanel_Intro#1] [!code-vbWrapPanel_Intro#1] [!code-xamlWrapPanel_Intro#1]
The compiled application yields a new UI that looks like this.
xref:System.Windows.Controls.Panel elements can be nested within each other in order to produce complex layouts. This can prove very useful in situations where one xref:System.Windows.Controls.Panel is ideal for a portion of a UI, but may not meet the needs of a different portion of the UI.
There is no practical limit to the amount of nesting that your application can support, however, it is generally best to limit your application to only use those panels that are actually necessary for your desired layout. In many cases, a xref:System.Windows.Controls.Grid element can be used instead of nested panels due to its flexibility as a layout container. This can increase performance in your application by keeping unnecessary elements out of the tree.
The following example demonstrates how to create a UI that takes advantage of nested xref:System.Windows.Controls.Panel elements in order to achieve a specific layout. In this particular case, a xref:System.Windows.Controls.DockPanel element is used to provide UI structure, and nested xref:System.Windows.Controls.StackPanel elements, a xref:System.Windows.Controls.Grid, and a xref:System.Windows.Controls.Canvas are used to position child elements precisely within the parent xref:System.Windows.Controls.DockPanel.
[!code-csharpNested_Panels#1] [!code-vbNested_Panels#1]
The compiled application yields a new UI that looks like this.
While WPF provides an array of flexible layout controls, custom layout behaviors can also be achieved by overriding the xref:System.Windows.FrameworkElement.ArrangeOverride%2A and xref:System.Windows.FrameworkElement.MeasureOverride%2A methods. Custom sizing and positioning can be accomplished by defining new positioning behaviors within these override methods.
Similarly, custom layout behaviors based on derived classes (such as xref:System.Windows.Controls.Canvas or xref:System.Windows.Controls.Grid) can be defined by overriding their xref:System.Windows.FrameworkElement.ArrangeOverride%2A and xref:System.Windows.FrameworkElement.MeasureOverride%2A methods.
The following markup demonstrates how to create a custom xref:System.Windows.Controls.Panel element. This new xref:System.Windows.Controls.Panel, defined as PlotPanel, supports the positioning of child elements through the use of hard-coded x- and y- coordinates. In this example, a xref:System.Windows.Shapes.Rectangle element (not shown) is positioned at plot point 50 (x), and 50 (y).
[!code-cppPlotPanel#1] [!code-csharpPlotPanel#1] [!code-vbPlotPanel#1]
To view a more complex custom panel implementation, see Create a Custom Content-Wrapping Panel Sample.
WPF supports a number of features that assist in the creation of localizable UI.
All panel elements natively support the xref:System.Windows.FrameworkElement.FlowDirection%2A property, which can be used to dynamically re-flow content based on a user's locale or language settings. For more information, see xref:System.Windows.FrameworkElement.FlowDirection%2A.
The xref:System.Windows.Window.SizeToContent%2A property provides a mechanism that enables application developers to anticipate the needs of localized UI. Using the xref:System.Windows.SizeToContent.WidthAndHeight value of this property, a parent xref:System.Windows.Window always sizes dynamically to fit content and is not constrained by artificial height or width restrictions.
xref:System.Windows.Controls.DockPanel, xref:System.Windows.Controls.Grid, and xref:System.Windows.Controls.StackPanel are all good choices for localizable UI. xref:System.Windows.Controls.Canvas is not a good choice, however, because it positions content absolutely, making it difficult to localize.
For additional information on creating WPF applications with localizable user interfaces (UIs)s, see the Use Automatic Layout Overview.