Provides a mechanism for executing a method at specified intervals. This class cannot be inherited.
Assembly: mscorlib (in mscorlib.dll)
Thetype exposes the following members.
|Timer(TimerCallback)||Initializes a new instance of the class with an infinite interval and an infinite due time, using the newly created object as the state object.|
|Timer(TimerCallback, Object, Int32, Int32)||Initializes a new instance of the class, using a 32-bit signed integer to specify the time interval.|
|Timer(TimerCallback, Object, Int64, Int64)||Initializes a new instance of the class, using 64-bit signed integers to measure time intervals.|
|Timer(TimerCallback, Object, TimeSpan, TimeSpan)||Initializes a new instance of the class, using TimeSpan values to measure time intervals.|
|Timer(TimerCallback, Object, UInt32, UInt32)||Initializes a new instance of the class, using 32-bit unsigned integers to measure time intervals.|
|Change(Int32, Int32)||Changes the start time and the interval between method invocations for a timer, using 32-bit signed integers to measure time intervals.|
|Change(Int64, Int64)||Changes the start time and the interval between method invocations for a timer, using 64-bit signed integers to measure time intervals.|
|Change(TimeSpan, TimeSpan)||Changes the start time and the interval between method invocations for a timer, using TimeSpan values to measure time intervals.|
|Change(UInt32, UInt32)||Changes the start time and the interval between method invocations for a timer, using 32-bit unsigned integers to measure time intervals.|
|Dispose||Releases all resources used by the current instance of .|
|Dispose(WaitHandle)||Releases all resources used by the current instance of and signals when the timer has been disposed of.|
|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.)|
|ToString||Returns a string that represents the current object. (Inherited from Object.)|
Use a TimerCallback delegate to specify the method you want the to execute. The timer delegate is specified when the timer is constructed, and cannot be changed. The method does not execute on the thread that created the timer; it executes on a ThreadPool thread that is supplied by the system.
When you create a timer, you can specify an amount of time to wait before the first execution of the method (due time), and an amount of time to wait between subsequent executions (period). You can change these values or disable the timer by using the Change method.
As long as you are using a , you must keep a reference to it. As with any managed object, a is subject to garbage collection when there are no references to it. The fact that a is still active does not prevent it from being collected.
When a timer is no longer needed, use the Dispose method to free the resources held by the timer. To receive a signal when the timer is disposed, use the Dispose(WaitHandle) method overload that takes a WaitHandle. The WaitHandle is signaled when the timer has been disposed.
The callback method executed by the timer should be reentrant, because it is called on ThreadPool threads. The callback can be executed simultaneously on two thread pool threads if the timer interval is less than the time required to execute the callback, or if all thread pool threads are in use and the callback is queued multiple times.
is a simple, lightweight timer that uses callback methods and is served by thread pool threads. It is not recommended for scenarios in which the user interface must be updated, because its callbacks do not occur on the user interface thread. System.Windows.Threading.DispatcherTimer is a better choice in those scenarios, because its events are raised on the user interface thread.
The example displays its output in a TextBlock on the UI thread. To access the TextBlock from the callback thread, the example uses the Dispatcher property to obtain a Dispatcher object for the TextBlock, and then uses the Dispatcher.BeginInvoke method to make the cross-thread call.
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.
Imports System.Threading ' The following Imports are not required for the timer. They merely simplify ' the code. Imports System.Windows.Controls Imports System.Windows.Input ' The Example class holds a reference to the timer, and contains the ' event handler for the MouseLeftButtonUp events that control the demo. ' Public Class Example ' The Shared Demo method sets the starting message and creates an ' instance of Example, which hooks up the handler for the MouseLeftButtonUp ' event. Public Shared Sub Demo(ByVal outputBlock As TextBlock) outputBlock.Text &= "Click to create the timer." & vbLf Dim dummy As New Example(outputBlock) End Sub ' Instance data for the demo. Private phase As Integer = 0 Private t As Timer Public Sub New(ByVal outputBlock As TextBlock) ' Hook up the mouse event when a new Example object is created. Note ' that this keeps garbage collection from reclaiming the Example ' object. AddHandler outputBlock.MouseLeftButtonUp, AddressOf Me.MouseUp End Sub Private Sub MouseUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs) Dim outputBlock As TextBlock = CType(sender, TextBlock) If phase = 0 Then ' On the first click, create the timer. outputBlock.Text &= vbLf & "Creating the timer at " & _ DateTime.Now.ToString("h:mm:ss.fff") & _ ", to start in 1 second with a half-second interval." & vbLf & _ "Click to change the interval from 1/2 second to 1 second." & vbLf & vbLf ' Create a timer that invokes the callback method after one second ' (1000 milliseconds) and every 1/2 second thereafter. The TextBlock ' that is used for output is passed as the state object. Visual Basic ' infers the delegate type, as if you had typed the following: ' New TimerCallback(AddressOf MyTimerCallback) ' t = New Timer(AddressOf MyTimerCallback, outputBlock, 1000, 500) ElseIf phase = 1 Then ' On the next click, change the timer interval to every second. outputBlock.Text &= vbLf & "Changing the interval to one second." & vbLf & _ "Click to destroy the timer." & vbLf & vbLf t.Change(0, 1000) Else ' On the last click, destroy the timer and shut down the demo. outputBlock.Text &= vbLf & "Destroying the timer." & vbLf & _ "Refresh the page to run the demo again." RemoveHandler outputBlock.MouseLeftButtonUp, AddressOf Me.MouseUp t.Dispose() End If phase += 1 End Sub ' The shared callback method is invoked on a ThreadPool thread by the Timer. ' The state object is passed to the callback method on each invocation. In this ' example, the state object is the TextBlock that displays output. In order to ' update the TextBlock object, which is on the UI thread, you must make the ' cross-thread call by using the Dispatcher object that is associated with the ' TextBlock. Private Shared Sub MyTimerCallback(ByVal state As Object) Dim outputBlock As TextBlock = CType(state, TextBlock) Dim msg As String = DateTime.Now.ToString("h:mm:ss.fff") & _ " MyTimerCallback was called." & vbLf outputBlock.Dispatcher.BeginInvoke(displayHelper, outputBlock, msg) End Sub ' The DisplayOutput helper method and its delegate, displayHelper, are used by ' the BeginInvoke method of the Dispatcher object. Private Shared displayHelper _ As New Action(Of TextBlock, String)(AddressOf DisplayOutput) Private Shared Sub DisplayOutput(ByVal tb As TextBlock, ByVal msg As String) tb.Text &= msg End Sub End Class ' This example produces output similar to the following: ' 'Click to create the timer. ' 'Creating the timer at 3:17:36.980, to start in 1 second with a half-second interval. 'Click to change the interval from 1/2 second to 1 second. ' '3:17:38.072 MyTimerCallback was called. '3:17:38.586 MyTimerCallback was called. '3:17:39.101 MyTimerCallback was called. '3:17:39.580 MyTimerCallback was called. ' 'Changing the interval to one second. 'Click to destroy the timer. ' '3:17:39.656 MyTimerCallback was called. '3:17:40.689 MyTimerCallback was called. ' 'Destroying the timer. 'Refresh the page to run the demo again.
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.