Question

I am writing a WPF application.
I want to trigger an event once the mouse stops moving.

This is how I tried to do it. I created a timer which counts down to 5 seconds. This timer is “reset” every time the mouse moves.
This idea is that the moment the mouse stops moving, the timer stops being reset, and counts down from 5 to zero, and then calls the tick event handler, which displays a message box.

Well, it doesn’t work as expected, and it floods me with alert messages. What am I doing wrong?

DispatcherTimer timer;

private void Window_MouseMove(object sender, MouseEventArgs e)
{
    timer = new DispatcherTimer();
    timer.Interval = new TimeSpan(0, 0, 5);
    timer.Tick += new EventHandler(timer_Tick);
    timer.Start();
}

void timer_Tick(object sender, EventArgs e)
{
    MessageBox.Show("Mouse stopped moving");
}

Answer 1

You need to unhook the event before hooking it again like this –

private void poc_MouseMove(object sender, MouseEventArgs e)
{
   if (timer != null)
   {
      timer.Tick-= timer_Tick;
   }
   timer = new DispatcherTimer();
   timer.Interval = new TimeSpan(0, 0, 5);
   timer.Tick += new EventHandler(timer_Tick);
   timer.Start();
}

Explanation

What you doing is whenever a mouse moves, you create a new instance of DispatcherTimer and hook Tick event to it without unhooking the event for previous instance. Hence, you see flooded messages once timer stops for all the instances.

Also, you should unhook it otherwise previous instance won’t be garbage collected since they are still strongly referenced.