Was this page helpful?
Additional feedback?
1500 characters remaining
Export (0) Print
Expand All

Timer Constructor (TimerCallback, Object, Int32, Int32)


Initializes a new instance of the Timer class, using a 32-bit signed integer to specify the time interval.

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

public Timer(
	TimerCallback callback,
	object state,
	int dueTime,
	int period


Type: System.Threading.TimerCallback

A TimerCallback delegate representing a method to be executed.

Type: System.Object

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

Type: System.Int32

The amount of time to delay before callback is invoked, in milliseconds. Specify Timeout.Infinite to prevent the timer from starting. Specify zero (0) to start the timer immediately.

Type: System.Int32

The time interval between invocations of callback, in milliseconds. Specify Timeout.Infinite to disable periodic signaling.

Exception Condition

The dueTime or period parameter is negative and is not equal to Timeout.Infinite.


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 Timeout.Infinite, 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 Timeout.Infinite and dueTime is not Timeout.Infinite, 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.

using System;
using System.Threading;

class TimerExample
    static void Main()
        // Create an event to signal the timeout count threshold in the
        // timer callback.
        AutoResetEvent autoEvent     = new AutoResetEvent(false);

        StatusChecker  statusChecker = new StatusChecker(10);

        // Create an inferred delegate that invokes methods for the timer.
        TimerCallback tcb = statusChecker.CheckStatus;

        // Create a timer that signals the delegate to invoke 
        // CheckStatus after one second, and every 1/4 second 
        // thereafter.
        Console.WriteLine("{0} Creating timer.\n", 
        Timer stateTimer = new Timer(tcb, autoEvent, 1000, 250);

        // When autoEvent signals, change the period to every
        // 1/2 second.
        autoEvent.WaitOne(5000, false);
        stateTimer.Change(0, 500);
        Console.WriteLine("\nChanging period.\n");

        // When autoEvent signals the second time, dispose of 
        // the timer.
        autoEvent.WaitOne(5000, false);
        Console.WriteLine("\nDestroying timer.");

class StatusChecker
    private int invokeCount;
    private int  maxCount;

    public StatusChecker(int count)
        invokeCount  = 0;
        maxCount = count;

    // This method is called by the timer delegate.
    public void CheckStatus(Object stateInfo)
        AutoResetEvent autoEvent = (AutoResetEvent)stateInfo;
        Console.WriteLine("{0} Checking status {1,2}.", 

        if(invokeCount == maxCount)
            // Reset the counter and signal Main.
            invokeCount  = 0;

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top
Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
© 2015 Microsoft