This article demonstrates how to implement timer in WPF
using the DispatchTimer class.
In this article and the attached project, I am going to
create a WPF application that has a ListBox control and this control is being
updated every second with current time. The
application looks like Figure 1.
Figure 1
Creating a DispatchTimer
XAML does not support any timer feature and WPF does not
have a Timer control or class. The DispatchTimer class defined in the
System.Windows.Threading namespace is used to add timer functionality in WPF.
The following code snippet creates a DispatchTimer object.
DispatcherTimer
dispatcherTimer = new DispatcherTimer();
Setting Tick and Interval
The Tick event handler executes when a DispatchTimer is
started on a given Interval. The following code snippet sets the Tick and
Interval of a DispatchTimer.
dispatcherTimer.Tick += new EventHandler(dispatcherTimer_Tick);
dispatcherTimer.Interval = new TimeSpan(0, 0,
1);
Start DispatchTimer
The Start method is used to start a DispatchTimer.
dispatcherTimer.Start();
Complete Code Example
The code snippet in
Listing 1 creates a DispatchTimer, sets its Tick event and Interval property
and calls its Start method. The Start method starts the timer and the Tick
event handler is executed on the given Interval value. In this code, on the
Tick event handler, I update a ListBox control and add the current time. I also
set the selected item of the ListBox to the currently added item and make sure
this item is visible in the ListView.
private void Window_Loaded(object
sender, RoutedEventArgs e)
{
DispatcherTimer
dispatcherTimer = new DispatcherTimer();
dispatcherTimer.Tick += new EventHandler(dispatcherTimer_Tick);
dispatcherTimer.Interval = new TimeSpan(0, 0,
1);
dispatcherTimer.Start();
}
private void dispatcherTimer_Tick(object
sender, EventArgs e)
{
listBox1.Items.Add(DateTime.Now.Hour.ToString()
+ ":" +
DateTime.Now.Second.ToString());
CommandManager.InvalidateRequerySuggested();
listBox1.Items.MoveCurrentToLast();
listBox1.SelectedItem =
listBox1.Items.CurrentItem;
listBox1.ScrollIntoView(listBox1.Items.CurrentItem);
}
Listing 1
Complete Code Example in VB.NET
Imports
System.Windows.Threading
Class Window1
Private Sub Window_Loaded(ByVal
sender As System.Object,
ByVal e As
System.Windows.RoutedEventArgs) _
Handles MyBase.Loaded
Dim dt As DispatcherTimer
= New DispatcherTimer()
AddHandler
dt.Tick, AddressOf dispatcherTimer_Tick
dt.Interval = New TimeSpan(0, 0, 1)
dt.Start()
End Sub
Public Sub dispatcherTimer_Tick(ByVal
sender As Object,
ByVal e As EventArgs)
listBox1.Items.Add(DateTime.Now.Hour.ToString() + ":" + DateTime.Now.Second.ToString())
CommandManager.InvalidateRequerySuggested()
listBox1.Items.MoveCurrentToLast()
listBox1.SelectedItem = listBox1.Items.CurrentItem
listBox1.ScrollIntoView(listBox1.Items.CurrentItem)
End Sub
End Class
Summary
In this article, I discussed how we can create a DispatchTimer
control to build timer applications in WPF and C#. We saw, how to update a ListBox control every
second with the current time.