Continuation of the task in the user interface thread, when launched from the background thread

Question

If the following code is running in the background thread, how can I continue with Continue using the main thread?

var task = Task.Factory.StartNew(() => Whatever()); task.ContinueWith(NeedThisMethodToBeOnUiThread), TaskScheduler.FromCurrentSynchronizationContext()) 

The above will not work because the current synchronization context is already a background thread.

Answer 1

You need to get a link to TaskScheduler.FromCurrentSynchronizationContext () from the user interface stream and pass it on.

Similar to this. http://reedcopsey.com/2009/11/17/synchronizing-net-4-tasks-with-the-ui-thread/

 private void Form1_Load(object sender, EventArgs e) { // This requires a label titled "label1" on the form... // Get the UI thread context var context = TaskScheduler.FromCurrentSynchronizationContext(); this.label1.Text = "Starting task..."; // Start a task - this runs on the background thread... Task task = Task.Factory.StartNew( () => { // Do some fake work... double j = 100; Random rand = new Random(); for (int i = 0; i < 10000000; ++i) { j *= rand.NextDouble(); } // It possible to start a task directly on // the UI thread, but not common... var token = Task.Factory.CancellationToken; Task.Factory.StartNew(() => { this.label1.Text = "Task past first work section..."; }, token, TaskCreationOptions.None, context); // Do a bit more work Thread.Sleep(1000); }) // More commonly, we'll continue a task with a new task on // the UI thread, since this lets us update when our // "work" completes. .ContinueWith(_ => this.label1.Text = "Task Complete!", context); }