Articolo
11/17/2011

Label Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Displays a caption, required field indicator, and validation error indicator for an associated control.

Inheritance Hierarchy

System.Object
  System.Windows.DependencyObject
    System.Windows.UIElement
      System.Windows.FrameworkElement
        System.Windows.Controls.Control
          System.Windows.Controls.ContentControl
            System.Windows.Controls.Label

Namespace: System.Windows.Controls
Assembly: System.Windows.Controls.Data.Input (in System.Windows.Controls.Data.Input.dll)

Syntax

'Declaration
<TemplateVisualStateAttribute(Name := "Invalid", GroupName := "ValidationStates")> _
<TemplateVisualStateAttribute(Name := "Disabled", GroupName := "CommonStates")> _
<TemplateVisualStateAttribute(Name := "Normal", GroupName := "CommonStates")> _
<TemplateVisualStateAttribute(Name := "Valid", GroupName := "ValidationStates")> _
<TemplateVisualStateAttribute(Name := "NotRequired", GroupName := "RequiredStates")> _
<TemplateVisualStateAttribute(Name := "Required", GroupName := "RequiredStates")> _
Public Class Label _
    Inherits ContentControl

[TemplateVisualStateAttribute(Name = "Invalid", GroupName = "ValidationStates")]
[TemplateVisualStateAttribute(Name = "Disabled", GroupName = "CommonStates")]
[TemplateVisualStateAttribute(Name = "Normal", GroupName = "CommonStates")]
[TemplateVisualStateAttribute(Name = "Valid", GroupName = "ValidationStates")]
[TemplateVisualStateAttribute(Name = "NotRequired", GroupName = "RequiredStates")]
[TemplateVisualStateAttribute(Name = "Required", GroupName = "RequiredStates")]
public class Label : ContentControl

<sdk:Label .../>
-or-
<sdk:Label>
  singleObject
</sdk:Label>
-or-
<sdk:Label>stringContent</sdk:Label>

XAML Values

singleObject
A single object element that declares the content.
stringContent
A string that is displayed as content through the default template ContentPresenter. For more information, see "String Content of a ContentControl" section of ContentControl.

The Label type exposes the following members.

Constructors

	Name	Description
	Label	Initializes a new instance of the Label class.

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Properties

	Name	Description
	ActualHeight	Gets the rendered height of a FrameworkElement. (Inherited from FrameworkElement.)
	ActualWidth	Gets the rendered width of a FrameworkElement. (Inherited from FrameworkElement.)
	AllowDrop	Gets or sets a value that determines whether this UIElement can be a drop target for purposes of Silverlight drag-and-drop operations. (Inherited from UIElement.)
	Background	Gets or sets a brush that provides the background of the control. (Inherited from Control.)
	BorderBrush	Gets or sets a brush that describes the border background of a control. (Inherited from Control.)
	BorderThickness	Gets or sets the border thickness of a control. (Inherited from Control.)
	CacheMode	Gets or sets a value that indicates that rendered content should be cached when possible. (Inherited from UIElement.)
	CharacterSpacing	Gets or sets the distance between characters of text in the control measured in 1000ths of the font size. (Inherited from Control.)
	Clip	Gets or sets the Geometry used to define the outline of the contents of a UIElement. (Inherited from UIElement.)
	Content	Gets or sets the value of the ContentControl dependency property. (Inherited from ContentControl.)
	ContentTemplate	Gets or sets the data template that is used to display the content of the ContentControl. (Inherited from ContentControl.)
	Cursor	Gets or sets the cursor image that displays while the mouse pointer is over a FrameworkElement. (Inherited from FrameworkElement.)
	DataContext	Gets or sets the data context for a FrameworkElement when it participates in data binding. (Inherited from FrameworkElement.)
	DefaultStyleKey	Gets or sets the key that references the default style for the control. (Inherited from Control.)
	DesiredSize	Gets the size that this UIElement computed during the measure pass of the layout process. (Inherited from UIElement.)
	Dispatcher	Gets the Dispatcher this object is associated with. (Inherited from DependencyObject.)
	Effect	Gets or sets the pixel shader effect to use for rendering this UIElement. (Inherited from UIElement.)
	FlowDirection	Gets or sets the direction that text and other user interface elements flow within any parent element that controls their layout. (Inherited from FrameworkElement.)
	FontFamily	Gets or sets the font used to display text in the control. (Inherited from Control.)
	FontSize	Gets or sets the size of the text in this control. (Inherited from Control.)
	FontStretch	Gets or sets the degree to which a font is condensed or expanded on the screen. (Inherited from Control.)
	FontStyle	Gets or sets the style in which the text is rendered. (Inherited from Control.)
	FontWeight	Gets or sets the thickness of the specified font. (Inherited from Control.)
	Foreground	Gets or sets a brush that describes the foreground color. (Inherited from Control.)
	Height	Gets or sets the suggested height of a FrameworkElement. (Inherited from FrameworkElement.)
	HorizontalAlignment	Gets or sets the horizontal alignment characteristics that are applied to a FrameworkElement when it is composed in a layout parent, such as a panel or items control. (Inherited from FrameworkElement.)
	HorizontalContentAlignment	Gets or sets the horizontal alignment of the control's content. (Inherited from Control.)
	IsEnabled	Gets or sets a value indicating whether the user can interact with the control. (Inherited from Control.)
	IsHitTestVisible	Gets or sets whether the contained area of this UIElement can return true values for hit testing. (Inherited from UIElement.)
	IsRequired	Gets or sets a value that indicates whether the property bound to the Target field is required.
	IsTabStop	Gets or sets a value that indicates whether a control is included in tab navigation. (Inherited from Control.)
	IsValid	Gets a value that indicates whether the Target field data is valid.
	Language	Gets or sets localization/globalization language information that applies to a FrameworkElement. (Inherited from FrameworkElement.)
	Margin	Gets or sets the outer margin of a FrameworkElement. (Inherited from FrameworkElement.)
	MaxHeight	Gets or sets the maximum height constraint of a FrameworkElement. (Inherited from FrameworkElement.)
	MaxWidth	Gets or sets the maximum width constraint of a FrameworkElement. (Inherited from FrameworkElement.)
	MinHeight	Gets or sets the minimum height constraint of a FrameworkElement. (Inherited from FrameworkElement.)
	MinWidth	Gets or sets the minimum width constraint of a FrameworkElement. (Inherited from FrameworkElement.)
	Name	Gets or sets the identifying name of the object. When a XAML processor creates the object tree from XAML markup, run-time code can refer to the XAML-declared object by this name. (Inherited from FrameworkElement.)
	Opacity	Gets or sets the degree of the object's opacity. (Inherited from UIElement.)
	OpacityMask	Gets or sets the brush used to alter the opacity of regions of this object. (Inherited from UIElement.)
	Padding	Gets or sets the padding inside a control. (Inherited from Control.)
	Parent	Gets the parent object of this FrameworkElement in the object tree. (Inherited from FrameworkElement.)
	Projection	Gets or sets the perspective projection (3-D effect) to apply when rendering this UIElement. (Inherited from UIElement.)
	PropertyPath	Gets or sets the path to the dependency property on the DataContext of the Target control that this Label is associated with.
	RenderSize	Gets the final render size of a UIElement. (Inherited from UIElement.)
	RenderTransform	Gets or sets transform information that affects the rendering position of a UIElement. (Inherited from UIElement.)
	RenderTransformOrigin	Gets or sets the origin point of any possible render transform declared by RenderTransform, relative to the bounds of the UIElement. (Inherited from UIElement.)
	Resources	Gets the locally defined resource dictionary. In XAML, you can establish resource items as child object elements of a frameworkElement.Resources property element, through XAML implicit collection syntax. (Inherited from FrameworkElement.)
	Style	Gets or sets an instance Style that is applied for this object during rendering. (Inherited from FrameworkElement.)
	TabIndex	Gets or sets a value that determines the order in which elements receive focus when the user navigates through controls by using the TAB key. (Inherited from Control.)
	TabNavigation	Gets or sets a value that modifies how tabbing and TabIndex work for this control. (Inherited from Control.)
	Tag	Gets or sets an arbitrary object value that can be used to store custom information about this object. (Inherited from FrameworkElement.)
	Target	Gets or sets the control that this Label is associated with.
	Template	Gets or sets a control template. (Inherited from Control.)
	Triggers	Gets the collection of triggers for animations that are defined for a FrameworkElement. (Inherited from FrameworkElement.)
	UseLayoutRounding	Gets or sets a value that determines whether rendering for the object and its visual subtree should use rounding behavior that aligns rendering to whole pixels. (Inherited from UIElement.)
	VerticalAlignment	Gets or sets the vertical alignment characteristics that are applied to a FrameworkElement when it is composed in a parent object such as a panel or items control. (Inherited from FrameworkElement.)
	VerticalContentAlignment	Gets or sets the vertical alignment of the control's content. (Inherited from Control.)
	Visibility	Gets or sets the visibility of a UIElement. A UIElement that is not visible does not render and does not communicate its desired size to layout. (Inherited from UIElement.)
	Width	Gets or sets the width of a FrameworkElement. (Inherited from FrameworkElement.)

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Methods

	Name	Description
	AddHandler	Adds a routed event handler for a specified routed event, adding the handler to the handler collection on the current element. Specify handledEventsToo as true to have the provided handler be invoked for routed event that had already been marked as handled by another element along the event route. (Inherited from UIElement.)
	ApplyTemplate	Loads the relevant control template so that its parts can be referenced. (Inherited from Control.)
	Arrange	Positions child objects and determines a size for a UIElement. Parent objects that implement custom layout for their child elements should call this method from their layout override implementations to form a recursive layout update. (Inherited from UIElement.)
	ArrangeOverride	Provides the behavior for the Arrange pass of Silverlight layout. Classes can override this method to define their own Arrange pass behavior. (Inherited from FrameworkElement.)
	CaptureMouse	Sets mouse capture to a UIElement. (Inherited from UIElement.)
	CheckAccess	Determines whether the calling thread has access to this object. (Inherited from DependencyObject.)
	ClearValue	Clears the local value of a dependency property. (Inherited from DependencyObject.)
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	FindName	Retrieves an object that has the specified identifier name. (Inherited from FrameworkElement.)
	Focus	Attempts to set the focus on the control. (Inherited from Control.)
	GetAnimationBaseValue	Returns any base value established for a Silverlight dependency property, which would apply in cases where an animation is not active. (Inherited from DependencyObject.)
	GetBindingExpression	Retrieves the BindingExpression for a dependency property where a binding is established. (Inherited from FrameworkElement.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetTemplateChild	Retrieves the named element in the instantiated ControlTemplate visual tree. (Inherited from Control.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetValue	Returns the current effective value of a dependency property from a DependencyObject. (Inherited from DependencyObject.)
	InvalidateArrange	Invalidates the arrange state (layout) for a UIElement. After the invalidation, the UIElement will have its layout updated, which will occur asynchronously. (Inherited from UIElement.)
	InvalidateMeasure	Invalidates the measurement state (layout) for a UIElement. (Inherited from UIElement.)
	Measure	Updates the DesiredSize of a UIElement. Typically, objects that implement custom layout for their layout children call this method from their own MeasureOverride implementations to form a recursive layout update. (Inherited from UIElement.)
	MeasureOverride	Provides the behavior for the Measure pass of Silverlight layout. Classes can override this method to define their own Measure pass behavior. (Inherited from FrameworkElement.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	OnApplyTemplate	Builds the visual tree for the Label control when a new template is applied. (Overrides FrameworkElement.OnApplyTemplate().)
	OnContentChanged	Called when the value of the Content property changes. (Overrides ContentControl.OnContentChanged(Object, Object).)
	OnCreateAutomationPeer	Returns a LabelAutomationPeer for use by the Silverlight automation infrastructure. (Overrides UIElement.OnCreateAutomationPeer().)
	OnDragEnter	Called before the DragEnter event occurs. (Inherited from Control.)
	OnDragLeave	Called before the DragLeave event occurs. (Inherited from Control.)
	OnDragOver	Called before the DragOver event occurs. (Inherited from Control.)
	OnDrop	Called before the Drop event occurs. (Inherited from Control.)
	OnGotFocus	Called before the GotFocus event occurs. (Inherited from Control.)
	OnKeyDown	Called before the KeyDown event occurs. (Inherited from Control.)
	OnKeyUp	Called before the KeyUp event occurs. (Inherited from Control.)
	OnLostFocus	Called before the LostFocus event occurs. (Inherited from Control.)
	OnLostMouseCapture	Called before the LostMouseCapture event occurs to provide handling for the event in a derived class without attaching a delegate. (Inherited from Control.)
	OnMouseEnter	Called before the MouseEnter event occurs. (Inherited from Control.)
	OnMouseLeave	Called before the MouseLeave event occurs. (Inherited from Control.)
	OnMouseLeftButtonDown	Called before the MouseLeftButtonDown event occurs. (Inherited from Control.)
	OnMouseLeftButtonUp	Called before the MouseLeftButtonUp event occurs. (Inherited from Control.)
	OnMouseMove	Called before the MouseMove event occurs. (Inherited from Control.)
	OnMouseRightButtonDown	Called before the MouseRightButtonDown event occurs. (Inherited from Control.)
	OnMouseRightButtonUp	Called before the MouseRightButtonUp event occurs. (Inherited from Control.)
	OnMouseWheel	Called before the MouseWheel event occurs to provide handling for the event in a derived class without attaching a delegate. (Inherited from Control.)
	OnTextInput	Called before the TextInput event occurs. (Inherited from Control.)
	OnTextInputStart	Called before the TextInputStart event occurs. (Inherited from Control.)
	OnTextInputUpdate	Called before the TextInputUpdate event occurs. (Inherited from Control.)
	ReadLocalValue	Returns the local value of a dependency property, if a local value is set. (Inherited from DependencyObject.)
	Refresh	Reloads the metadata from the Target element.
	ReleaseMouseCapture	Removes mouse capture from a UIElement. After this call, typically no object holds mouse capture. (Inherited from UIElement.)
	RemoveHandler	Removes the specified routed event handler from this UIElement. (Inherited from UIElement.)
	SetBinding	Attaches a binding to a FrameworkElement, using the provided binding object, and returns a BindingExpressionBase for possible later use. (Inherited from FrameworkElement.)
	SetValue	Sets the local value of a dependency property on a DependencyObject. (Inherited from DependencyObject.)
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	TransformToVisual	Returns a transform object that can be used to transform coordinates from the UIElement to the specified object. (Inherited from UIElement.)
	UpdateLayout	Ensures that all positions of child objects of a UIElement are properly updated for layout. (Inherited from UIElement.)

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Events

	Name	Description
	BindingValidationError	Occurs when a data validation error is reported by a binding source. (Inherited from FrameworkElement.)
	DataContextChanged	Occurs when the data context for this element changes. (Inherited from FrameworkElement.)
	DragEnter	Occurs when the input system reports an underlying drag event with this element as the target. (Inherited from UIElement.)
	DragLeave	Occurs when the input system reports an underlying drag event with this element as the origin. (Inherited from UIElement.)
	DragOver	Occurs when the input system reports an underlying drag event with this element as the potential drop target. (Inherited from UIElement.)
	Drop	Occurs when the input system reports an underlying drop event with this element as the drop target. (Inherited from UIElement.)
	GotFocus	Occurs when a UIElement receives focus. (Inherited from UIElement.)
	IsEnabledChanged	Occurs when the IsEnabled property changes. (Inherited from Control.)
	KeyDown	Occurs when a keyboard key is pressed while the UIElement has focus. (Inherited from UIElement.)
	KeyUp	Occurs when a keyboard key is released while the UIElement has focus. (Inherited from UIElement.)
	LayoutUpdated	Occurs when the layout of the Silverlight visual tree changes. (Inherited from FrameworkElement.)
	Loaded	Occurs when a FrameworkElement has been constructed and added to the object tree. (Inherited from FrameworkElement.)
	LostFocus	Occurs when a UIElement loses focus. (Inherited from UIElement.)
	LostMouseCapture	Occurs when the UIElement loses mouse capture. (Inherited from UIElement.)
	MediaCommand	Occurs when a button is pressed on a remote control. (Inherited from UIElement.)
	MouseEnter	Occurs when the mouse (or a stylus) enters the bounding area of a UIElement. (Inherited from UIElement.)
	MouseLeave	Occurs when the mouse (or the stylus) leaves the bounding area of a UIElement. (Inherited from UIElement.)
	MouseLeftButtonDown	Occurs when the left mouse button is pressed (or when the tip of the stylus touches the tablet) while the mouse pointer is over a UIElement. (Inherited from UIElement.)
	MouseLeftButtonUp	Occurs when the left mouse button is released (or the tip of the stylus is removed from the tablet) while the mouse (or the stylus) is over a UIElement (or while a UIElement holds mouse capture). (Inherited from UIElement.)
	MouseMove	Occurs when the coordinate position of the mouse (or stylus) changes while over a UIElement (or while a UIElement holds mouse capture). (Inherited from UIElement.)
	MouseRightButtonDown	Occurs when the right mouse button is pressed while the mouse pointer is over a UIElement. (Inherited from UIElement.)
	MouseRightButtonUp	Occurs when the right mouse button is released while the mouse pointer is over a UIElement. However, this event will only be raised if a caller marks the preceding MouseRightButtonDown event as handled; see Remarks. (Inherited from UIElement.)
	MouseWheel	Occurs when the user rotates the mouse wheel while the mouse pointer is over a UIElement, or the UIElement has focus. (Inherited from UIElement.)
	SizeChanged	Occurs when either the ActualHeight or the ActualWidth properties change value on a FrameworkElement. (Inherited from FrameworkElement.)
	TextInput	Occurs when a UI element gets text in a device-independent manner. (Inherited from UIElement.)
	TextInputStart	Occurs when a UI element initially gets text in a device-independent manner. (Inherited from UIElement.)
	TextInputUpdate	Occurs when text continues to be composed via an input method editor (IME). (Inherited from UIElement.)
	Unloaded	Occurs when this object is no longer connected to the main object tree. (Inherited from FrameworkElement.)

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Fields

	Name	Description
	IsRequiredProperty	Identifies the IsRequired dependency property.
	IsValidProperty	Identifies the IsValid dependency property.
	PropertyPathProperty	Identifies the PropertyPath dependency property.
	TargetProperty	Identifies the Target dependency property.

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Remarks

A Label control displays a caption, required field indicator, and validation error indicator to the user. It is typically used together with an input control, such as a TextBox. If you do not need to display required field or validation indicators, you can use the TextBlock control instead.

To associate a Label with another control, you set the Target property of the Label. The Target is a reference to a UIElement. You can set the Target in code or through an ElementName binding in XAML.

When the Target property is set, a Label inspects each DependencyProperty on the Target control for a Binding. For each Binding that is found, it inspects the Source of the Binding for metadata. The metadata can be used to set the caption text, specify whether the field is required, and specify validation rules. If the Target control has more than one Binding, you can specify the one to retrieve metadata from by setting the PropertyPath property.

You use the Content property to set the caption of a Label. For more information about the content model for Label, see Control Content Models. If the property associated with the Label has a DisplayAttribute and the Name property is not nulla null reference (Nothing in Visual Basic) or an empty string, the Content will be set to the value of the DisplayAttribute.Name property. For more information, see Using Data Annotations to Customize Data Classes.

By default, the Label control indicates a required field by making the caption text bold. You put the Label in the Required visual state by setting the IsRequired property to true, or by putting a RequiredAttribute on the property the Label is associated with.

By default, the Label control indicates a validation error by making the caption text red. When the Target property is set, a Label responds to the BindingValidationError event for the Target control. It changes to its Invalid visual state when an error occurs, and to its Valid visual state when the error is resolved. In order to receive error notifications, you must set the ValidatesOnExceptions and NotifyOnValidationError properties on the Target controls Binding to true.

Note:
The Label control in Silverlight does not provide support for access keys.

Note:
The Label control is available as part of the libraries in the Silverlight Software Development Kit (SDK). For more information, see the Silverlight Tools.

Customizing the Label Control

To apply the same property settings to multiple Label controls, use the Style property. To change the visual structure and visual behavior of a Label, copy and modify its default style and template. For more information, see Control Customization.

Dependency properties for this control might be set by the default style of the control. If a dependency property for a Label is set by its default style, the property might change from its default value when the Label appears in the application. For more information, see Dependency Property Value Precedence. You can get the default style and template for Label from Label Styles and Templates.

Note:
Setting a visual property will only have an effect if that property is both present in Label control's default template and is set by using a TemplateBinding. You can find a list of visual properties in the "Changing the Visual Structure of a Control" section of Customizing the Appearance of an Existing Control by Using a ControlTemplate.

Examples

The following example demonstrates two Label controls on a form. The first Label is used unbound to identify a DatePicker control. The second Label is bound to a TextBox named tbIdNumber, which is bound to the IdNumber property of a Customer object. This example is part of a larger example available in the ValidationSummary class overview.

Run this sample

<!-- Unbound Date of Birth field -->
<sdk:Label Content="Date of Birth" IsRequired="True" Margin="5" />
<StackPanel Orientation="Horizontal" Grid.Column="1">
    <sdk:DatePicker Height="23" />
    <sdk:DescriptionViewer Description="Please enter your date of birth."/>
</StackPanel>

<!-- ID Number field -->
<sdk:Label Grid.Row="1" Margin="5" 
                 Target="{Binding ElementName=tbIdNumber}" />
<StackPanel Orientation="Horizontal" Grid.Column="1" Grid.Row="1">
    <TextBox x:Name="tbIdNumber" Height="23" Width="100"
             Text="{Binding IdNumber, Mode=TwoWay, 
                    ValidatesOnExceptions=true, NotifyOnValidationError=true}" />
    <sdk:DescriptionViewer Target="{Binding ElementName=tbIdNumber}"/>
</StackPanel>

Version Information

Silverlight

Supported in: 5, 4, 3

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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