Articolo
11/18/2011

DispatcherTimer Class

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

A timer that is integrated into the Dispatcher queue, which is processed at a specified interval of time and at a specified priority.

Inheritance Hierarchy

System.Object
System.Windows.Threading.DispatcherTimer

Namespace: System.Windows.Threading
Assembly: System.Windows (in System.Windows.dll)

Syntax

'Declaration
Public Class DispatcherTimer

public class DispatcherTimer

The DispatcherTimer type exposes the following members.

Constructors

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

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Properties

	Name	Description
	Interval	Gets or sets the amount of time between timer ticks.
	IsEnabled	Gets a value that indicates whether the timer is running.

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Methods

	Name	Description
	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.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Start	Starts the DispatcherTimer.
	Stop	Stops the DispatcherTimer.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Events

	Name	Description
	Tick	Occurs when the timer interval has elapsed.

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Remarks

The DispatcherTimer is reevaluated at the top of every DispatcherTimer loop.

Timers are not guaranteed to execute exactly when the time interval occurs, but they are guaranteed to not execute before the time interval occurs. This is because DispatcherTimer operations are placed on the DispatcherTimer queue like other operations. When the DispatcherTimer operation executes is dependent on the other jobs in the queue and their priorities.

If a System.Threading.Timer is used, it is worth noting that the Timer runs on a different thread then the user interface (UI) thread. In order to access objects on the UI thread, it is necessary to post the operation onto the UI thread using Dispatcher.BeginInvoke. This is unnecessary when using a DispatcherTimer.

A DispatcherTimer will keep an object alive whenever the object's methods are bound to the timer.

Examples

The following code example demonstrates how to use this class.

Private WithEvents counterPanel As Panel
Private WithEvents timer As DispatcherTimer = New DispatcherTimer()
Private counter As Integer = 0

Private Sub PanelClick(ByVal sender As System.Object, _
    ByVal e As System.Windows.Input.MouseButtonEventArgs) _
    Handles counterPanel.MouseLeftButtonDown

    If timer.IsEnabled Then timer.Stop() Else timer.Start()

End Sub

Private Sub TimerClick(ByVal sender As System.Object, _
    ByVal e As EventArgs) Handles timer.Tick

    counter += 1
    counterPanel.Children.Clear()
    Dim t As New TextBlock
    t.Text = counter.ToString
    counterPanel.Children.Add(t)

End Sub

Private Sub TestDispatcherTimer(ByVal p As Panel)

    Me.counterPanel = p
    timer.Interval = New TimeSpan(0, 0, 1)
    timer.Start()

End Sub

private void TestDispatcherTimer(Panel counterPanel)
{
    DispatcherTimer timer = new DispatcherTimer();
    int counter = 0;

    counterPanel.MouseLeftButtonDown += 
        delegate(object s, MouseButtonEventArgs args) {
            if (timer.IsEnabled) timer.Stop(); else timer.Start(); 
        };

    timer.Tick += 
        delegate(object s, EventArgs args) {
            counterPanel.Children.Clear();
            counterPanel.Children.Add( new TextBlock { 
                Text = counter++.ToString() });
        };

    timer.Interval = new TimeSpan(0, 0, 1); // one second
    timer.Start();
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

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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