Question

I know there is Thread.Sleep and System.Windows.Forms.Timer and Monitor.Wait in C# and Windows Forms. I just can’t seem to be able to figure out how to wait for X seconds and then do something else – without locking the thread.

I have a form with a button. On button click a timer shall start and wait for 5 seconds. After these 5 seconds some other control on the form is colored green. When using Thread.Sleep, the whole application would become unresponsive for 5 seconds – so how do I just “do something after 5 seconds”?

Answer 1

(transcribed from Ben as comment)

just use System.Windows.Forms.Timer. Set the timer for 5 seconds, and handle the Tick event. When the event fires, do the thing.

…and disable the timer (IsEnabled=false) before doing your work in oder to suppress a second.

The Tick event may be executed on another thread that cannot modify your gui, you can catch this:

private System.Windows.Forms.Timer myTimer = new System.Windows.Forms.Timer();

    private void StartAsyncTimedWork()
    {
        myTimer.Interval = 5000;
        myTimer.Tick += new EventHandler(myTimer_Tick);
        myTimer.Start();
    }

    private void myTimer_Tick(object sender, EventArgs e)
    {
        if (this.InvokeRequired)
        {
            /* Not on UI thread, reenter there... */
            this.BeginInvoke(new EventHandler(myTimer_Tick), sender, e);
        }
        else
        {
            lock (myTimer)
            {
                /* only work when this is no reentry while we are already working */
                if (this.myTimer.Enabled)
                {
                    this.myTimer.Stop();
                    this.doMyDelayedWork();
                    this.myTimer.Start(); /* optionally restart for periodic work */
                }
            }
        }
    }

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Just for completeness: with async/await, one can delay execute something very easy (one shot, never repeat the invocation):

private async Task delayedWork()
{
    await Task.Delay(5000);
    this.doMyDelayedWork();
}

//This could be a button click event handler or the like */
private void StartAsyncTimedWork()
{
    Task ignoredAwaitableResult = this.delayedWork();
}

For more, see "async and await" in MSDN.

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more completeness:
Depending on your Framework, there is a good chance you will have DispatcherTimer class that can handle the invocation internally (WPF-variants). (finde details in ms docs)