Timer.Change Method (TimeSpan, TimeSpan)
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Changes the start time and the interval between method invocations for a timer, using TimeSpan values to measure time intervals.
Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Function Change ( _
dueTime As TimeSpan, _
period As TimeSpan _
) As Boolean
public bool Change(
TimeSpan dueTime,
TimeSpan period
)
Parameters
- dueTime
Type: System.TimeSpan
The amount of time to delay before invoking the callback method that was specified when the Timer was constructed. Specify -1 (negative one) milliseconds to prevent the timer from restarting. Specify 0 (zero) to restart the timer immediately.
- period
Type: System.TimeSpan
The time interval between invocations of the callback method that was specified when the Timer was constructed. Specify -1 (negative one) milliseconds to disable periodic signaling.
Return Value
Type: System.Boolean
true if the timer was successfully updated; otherwise, false.
Exceptions
| Exception | Condition |
|---|---|
| ObjectDisposedException | The Timer has already been disposed. |
| ArgumentOutOfRangeException | The dueTime or period parameter is negative and is not equal to -1 (negative one) milliseconds. -or- The dueTime or period parameter is greater than 4294967294 (UInt32.MaxValue - 1) milliseconds. |
Remarks
The callback method is invoked once after dueTime elapses, and thereafter each time the time interval specified by period elapses.
If dueTime is 0 (zero), the callback method is invoked immediately. If dueTime is -1 (negative one) milliseconds, the callback method is never invoked; the timer is disabled but can be re-enabled by calling Change and specifying a positive value for dueTime.
If period is 0 (zero) or -1 (negative one) milliseconds, and dueTime is positive, the callback method is invoked once; the periodic behavior of the timer is disabled but can be re-enabled by calling Change and specifying a value greater than zero for period.
Examples
The following example demonstrates how to start a Timer and, after a number of invocations, change its period.
This example creates a timer, uses the Timer.Change method to change its interval, and then uses the Timer.Dispose method to destroy it.
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.
.gif "Note") Note: |
|---|
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
Public Class Example
' The Shared Demo method sets the starting message and hooks up the handler
' for the MouseLeftButtonUp event, which controls the demo.
Public Shared Sub Demo(ByVal outputBlock As TextBlock)
outputBlock.Text &= "Click to create the timer." & vbLf
Example.outputBlock = outputBlock
AddHandler outputBlock.MouseLeftButtonUp, AddressOf MouseUp
End Sub
' Data for the demo.
Private Shared phase As Integer = 0
Private Shared t As Timer
Private Shared outputBlock As TextBlock
Private Shared Sub MouseUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs)
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
' and every 1/2 second (500 milliseconds) thereafter. Visual Basic
' infers the delegate type, as if you had typed the following:
' New TimerCallback(AddressOf MyTimerCallback)
'
t = New Timer(AddressOf MyTimerCallback, Nothing, _
New TimeSpan(0, 0, 1), New TimeSpan(0, 0, 0, 0, 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(New TimeSpan(0), New TimeSpan(0, 0, 1))
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 MouseUp
t.Dispose()
End If
phase += 1
End Sub
' The shared callback method is invoked on a ThreadPool thread by the Timer. In
' this example, the state object is not used. 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 msg As String = DateTime.Now.ToString("h:mm:ss.fff") & _
" MyTimerCallback was called." & vbLf
outputBlock.Dispatcher.BeginInvoke(displayHelper, 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 String)(AddressOf DisplayOutput)
Private Shared Sub DisplayOutput(ByVal msg As String)
outputBlock.Text &= msg
End Sub
End Class
' This example produces output similar to the following:
'
'Click to create the timer.
'
'Creating the timer at 4:14:48.114, to start in 1 second with a half-second interval.
'Click to change the interval from 1/2 second to 1 second.
'
'4:14:49.221 MyTimerCallback was called.
'4:14:49.736 MyTimerCallback was called.
'4:14:50.211 MyTimerCallback was called.
'
'Changing the interval to one second.
'Click to destroy the timer.
'
'4:14:50.640 MyTimerCallback was called.
'4:14:51.676 MyTimerCallback was called.
'
'Destroying the timer.
'Refresh the page to run the demo again.
using System;
using System.Threading;
// The following Imports are not required for the timer. They merely simplify
// the code.
using System.Windows.Controls;
using System.Windows.Input;
public class Example
{
// The static Demo method sets the starting message and hooks up the handler
// for the MouseLeftButtonUp event, which controls the demo.
public static void Demo(TextBlock outputBlock)
{
outputBlock.Text += "Click to create the timer.\n";
Example.outputBlock = outputBlock;
outputBlock.MouseLeftButtonUp += new MouseButtonEventHandler(MouseUp);
}
// Data for the demo.
private static int phase = 0;
private static Timer t;
private static TextBlock outputBlock;
private static void MouseUp(object sender, MouseButtonEventArgs e)
{
if (phase==0)
{
// On the first click, create the timer.
outputBlock.Text += "\nCreating the timer at " +
DateTime.Now.ToString("h:mm:ss.fff") +
", to start in 1 second with a half-second interval.\n" +
"Click to change the interval from 1/2 second to 1 second.\n\n";
// 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. C# infers the
// delegate type, as if you had typed the following:
// new TimerCallback(MyTimerCallback)
//
t = new Timer(MyTimerCallback, outputBlock,
new TimeSpan(0, 0, 1), new TimeSpan(0, 0, 0, 0, 500));
}
else if (phase==1)
{
outputBlock.Text += "\nChanging the interval to one second.\n" +
"Click to destroy the timer.\n\n";
t.Change(new TimeSpan(0), new TimeSpan(0, 0, 1));
}
else
{
// On the last click, destroy the timer and shut down the demo.
outputBlock.Text += "\nDestroying the timer.\n" +
"Refresh the page to run the demo again.";
outputBlock.MouseLeftButtonUp -= new MouseButtonEventHandler(MouseUp);
t.Dispose();
}
phase += 1;
}
// The static callback method is invoked on a ThreadPool thread by the Timer. In
// this example, the state object is not used. 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 static void MyTimerCallback(object state)
{
TextBlock outputBlock = (TextBlock) state;
string msg = DateTime.Now.ToString("h:mm:ss.fff") + " MyTimerCallback was called.\n";
outputBlock.Dispatcher.BeginInvoke(delegate () { outputBlock.Text += msg; });
}
}
/* This example produces output similar to the following:
Click to create the timer.
Creating the timer at 4:27:38.623, to start in 1 second with a half-second interval.
Click to change the interval from 1/2 second to 1 second.
4:27:39.731 MyTimerCallback was called.
4:27:40.245 MyTimerCallback was called.
4:27:40.719 MyTimerCallback was called.
Changing the interval to one second.
Click to destroy the timer.
4:27:40.895 MyTimerCallback was called.
4:27:41.945 MyTimerCallback was called.
Destroying the timer.
Refresh the page to run the demo again.
*/
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, 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.