C# 4 and .NET 4

534 ❘ ChaPTer 20 threAds, tAsks, And synchrOnizAtiOn
If the time interval should be changed after creating the Timer object, you can pass new values with the
Change() method.
private static void ThreadingTimer()
{
var t1 = new System.Threading.Timer(
TimeAction, null, TimeSpan.FromSeconds(2),
TimeSpan.FromSeconds(3));
Thread.Sleep(15000);
}
t1.Dispose();
static void TimeAction(object o)
{
Console.WriteLine("System.Threading.Timer {0:T}", DateTime.Now);
}
code snippet TimerSample/Program.cs
The constructor of the Timer class from the System.Timers namespace requires just a time interval. The
method that should be invoked after the interval is specified by the Elapsed event. This event requires a
delegate of type ElapsedEventHandler, which requires object and ElapsedEventArgs parameters, as you
can see with the TimeAction method. The AutoReset property specifies whether the timer should be fired
repeatedly. If you set this property to false, the event is fired only once. Calling the Start method enables
the timer to fire the events. Instead of calling the Start method, you can set the Enabled property to true.
Behind the scenes Start() does nothing else. The Stop() method sets the Enabled property to false to
stop the timer.
private static void TimersTimer()
{
var t1 = new System.Timers.Timer(1000);
t1.AutoReset = true;
t1.Elapsed += TimeAction;
t1.Start();
Thread.Sleep(10000);
t1.Stop();
}
t1.Dispose();
static void TimeAction(object sender, System.Timers.ElapsedEventArgs e)
{
Console.WriteLine("System.Timers.Timer {0:T}", e.SignalTime );
}
eVenT-based asynChronous PaTTern
Earlier in this chapter, you saw the asynchronous pattern based on the IAsyncResult interface. With an
asynchronous callback, the callback thread is different from the calling thread. Using Windows Forms or
WPF, this is a problem, because Windows Forms and WPF controls are bound to a single thread. With every
control, you can invoke methods only from the thread that created the control. This also means that if you
have a background thread, you cannot directly access the UI controls from this thread.
The only methods with Windows Forms controls that you can invoke from a different thread than the creator
thread are Invoke(), BeginInvoke(), EndInvoke(), and the property InvokeRequired. BeginInvoke()
and EndInvoke() are asynchronous variants of Invoke(). These methods switch to the creator thread to
invoke the method that is assigned to a delegate parameter that you can pass to these methods. Using these
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