Sleep task (System.Threading.Tasks)

Question

I need to create thread which will replace photo in Windows Forms window, than waits for ~1second and restore the previous photo.

I thought that the following code:

TaskScheduler ui = TaskScheduler.FromCurrentSynchronizationContext();
var task = Task.Factory.StartNew(() =>
{
    pic.Image = Properties.Resources.NEXT;
    Thread.Sleep(1000);
    pic.Image = Properties.Resources.PREV;
}, CancellationToken.None, TaskCreationOptions.LongRunning, ui)

do the job, but unfortunately doesn't. It freezes main UI thread.

That's because it's not guaranteed that there is one thread per one task. One thread can be used for processing several tasks. Even TaskCreationOptions.LongRunning option can't help.

How I can fix it?

Answer 1

Thread.Sleep is a synchronous delay. If you want an asynchronous delay then use Task.Delay.

In C# 5, which is at present in beta release, you can simply say

await Task.Delay(whatever);

in an asynchronous method, and the method will automatically pick up where it left off.

If you are not using C# 5 then you can "manually" set whatever code you want to be the continuation of the delay yourself.