Timer Constructor (TimerCallback, Object, TimeSpan, TimeSpan)

Timer Constructor (TimerCallback, Object, TimeSpan, TimeSpan)

 

Initializes a new instance of the Timer class, using TimeSpan values to measure time intervals.

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

Public Sub New (
	callback As TimerCallback,
	state As Object,
	dueTime As TimeSpan,
	period As TimeSpan
)

Parameters

callback
Type: System.Threading.TimerCallback

A delegate representing a method to be executed.

state
Type: System.Object

An object containing information to be used by the callback method, or null.

dueTime
Type: System.TimeSpan

The amount of time to delay before the callback parameter invokes its methods. Specify negative one (-1) milliseconds to prevent the timer from starting. Specify zero (0) to start the timer immediately.

period
Type: System.TimeSpan

The time interval between invocations of the methods referenced by callback. Specify negative one (-1) milliseconds to disable periodic signaling.

Exception Condition
ArgumentOutOfRangeException

The number of milliseconds in the value of dueTime or period is negative and not equal to Timeout.Infinite, or is greater than Int32.MaxValue.

ArgumentNullException

The callback parameter is null.

The delegate specified by the callback parameter is invoked once after dueTime elapses, and thereafter each time the period time interval elapses.

If dueTime is zero (0), callback is invoked immediately. If dueTime is negative one (-1) milliseconds, callback is not invoked; the timer is disabled, but can be re-enabled by calling the Change method.

Because the Timer class has the same resolution as the system clock, which is approximately 15 milliseconds on Windows 7 and Windows 8 systems, the callback delegate executes at intervals defined by the resolution of the system clock if period is less than the resolution of the system clock. If period is zero (0) or negative one (-1) milliseconds and dueTime is positive, callback is invoked once; the periodic behavior of the timer is disabled, but can be re-enabled using the Change method.

The method specified for callback should be reentrant, because it is called on ThreadPool threads. The method can be executed simultaneously on two thread pool threads if the timer interval is less than the time required to execute the method, or if all thread pool threads are in use and the method is queued multiple times.

The following code example shows how to create a TimerCallback delegate and initialize a new instance of the Timer class.

Imports Microsoft.VisualBasic
Imports System
Imports System.Threading

Public Class TimerExample

    <MTAThread> _
    Shared Sub Main()

        Dim autoEvent As New AutoResetEvent(False)
        Dim statusChecker As New StatusChecker(10)

        ' Create the delegate that invokes methods for the timer.
        Dim timerDelegate As TimerCallback = _
            AddressOf statusChecker.CheckStatus

        Dim delayTime As New TimeSpan(0, 0, 1)
        Dim intervalTime As New TimeSpan(0, 0, 0, 0, 250)

        ' Create a timer that signals the delegate to invoke 
        ' CheckStatus after one second, and every 1/4 second 
        ' thereafter.
        Console.WriteLine("{0} Creating timer." & vbCrLf, _
            DateTime.Now.ToString("h:mm:ss.fff"))
        Dim stateTimer As Timer = New Timer( _
            timerDelegate, autoEvent, delayTime, intervalTime)

        ' When autoEvent signals, change the period to every 
        ' 1/2 second.
        autoEvent.WaitOne(5000, False)
        stateTimer.Change( _
            new TimeSpan(0), intervalTime.Add(intervalTime))
        Console.WriteLine(vbCrLf & "Changing period." & vbCrLf)

        ' When autoEvent signals the second time, dispose of 
        ' the timer.
        autoEvent.WaitOne(5000, False)
        stateTimer.Dispose()
        Console.WriteLine(vbCrLf & "Destroying timer.")

    End Sub
End Class

Public Class StatusChecker

    Dim invokeCount, maxCount As Integer 

    Sub New(count As Integer)
        invokeCount  = 0
        maxCount = count
    End Sub

    ' This method is called by the timer delegate.
    Sub CheckStatus(stateInfo As Object)
        Dim autoEvent As AutoResetEvent = _
            DirectCast(stateInfo, AutoResetEvent)
        invokeCount += 1
        Console.WriteLine("{0} Checking status {1,2}.", _
            DateTime.Now.ToString("h:mm:ss.fff"), _
            invokeCount.ToString())

        If invokeCount = maxCount Then

            ' Reset the counter and signal to stop the timer.
            invokeCount  = 0
            autoEvent.Set()
        End If
    End Sub

End Class

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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