DispatcherTimer Class

Definition

public ref class DispatcherTimer

public class DispatcherTimer

type DispatcherTimer = class

Public Class DispatcherTimer

Inheritance

Object

DispatcherTimer

Examples

The following example creates a DispatcherTimer that updates the contents of a Label and calls the InvalidateRequerySuggested method on the CommandManager.

A DispatcherTimer object named dispatcherTimer is created. The event handler dispatcherTimer_Tick is added to the Tick event of dispatcherTimer. The Interval is set to 1 second using a TimeSpan object, and the timer is started.

//  DispatcherTimer setup
dispatcherTimer = new System.Windows.Threading.DispatcherTimer();
dispatcherTimer.Tick += new EventHandler(dispatcherTimer_Tick);
dispatcherTimer.Interval = TimeSpan.FromSeconds(1);
dispatcherTimer.Start();

'  DispatcherTimer setup
dispatcherTimer = New Threading.DispatcherTimer()
AddHandler dispatcherTimer.Tick, AddressOf dispatcherTimer_Tick
dispatcherTimer.Interval = New TimeSpan(0,0,1)
dispatcherTimer.Start()

The Tick event handler updates a Label that displays the current second, and it calls InvalidateRequerySuggested on the CommandManager.

//  System.Windows.Threading.DispatcherTimer.Tick handler
//
//  Updates the current seconds display and calls
//  InvalidateRequerySuggested on the CommandManager to force 
//  the Command to raise the CanExecuteChanged event.
private void dispatcherTimer_Tick(object sender, EventArgs e)
{
    // Updating the Label which displays the current second
    lblSeconds.Content = DateTime.Now.Second;

    // Forcing the CommandManager to raise the RequerySuggested event
    CommandManager.InvalidateRequerySuggested();
}

'  System.Windows.Threading.DispatcherTimer.Tick handler
'
'  Updates the current seconds display and calls
'  InvalidateRequerySuggested on the CommandManager to force 
'  the Command to raise the CanExecuteChanged event.
Private Sub dispatcherTimer_Tick(ByVal sender As Object, ByVal e As EventArgs)
    ' Updating the Label which displays the current second
    lblSeconds.Content = Date.Now.Second

    ' Forcing the CommandManager to raise the RequerySuggested event
    CommandManager.InvalidateRequerySuggested()
End Sub

Remarks

The DispatcherTimer is reevaluated at the top of every Dispatcher 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 Dispatcher queue like other operations. When the DispatcherTimer operation executes is dependent on the other jobs in the queue and their priorities.

If a System.Timers.Timer is used in a WPF application, it is worth noting that the System.Timers.Timer runs on a different thread than the user interface (UI) thread. In order to access objects on the user interface (UI) thread, it is necessary to post the operation onto the Dispatcher of the user interface (UI) thread using Invoke or BeginInvoke. Reasons for using a DispatcherTimer as opposed to a System.Timers.Timer are that the DispatcherTimer runs on the same thread as the Dispatcher and a DispatcherPriority can be set on the DispatcherTimer.

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

Constructors

Properties

Methods

Events

Applies to