Tasks: ContinueWith on UI Thread

Sometimes we need to perform a task in the background, but then we want to update the UI when it is completed.

We can make use of a Task and the ContinueWith method so that we can chain tasks together. To ensure that a task is performed on a specific thread, we specify which TaskSheduler to use. To get the UI thread scheduler, we can use TaskScheduler.FromCurrentSynchronizationContext() when we are on the UI thread:

If we are going to run a background task:

var uiThread = TaskScheduler.FromCurrentSynchronizationContext();
Task.Run(() => {
    // do some work on a background thread
}).ContinueWith(task => {
    // do some work on the UI thread
}, uiThread);

If we need to carry a result from the previous background task:

var uiThread = TaskScheduler.FromCurrentSynchronizationContext();
Task.Run(() => {
    // do some work on a background thread

    // return a value for the next task
    return true;
}).ContinueWith(task => {
    // do some work on the UI thread

    if (task.Result) {
        // make use of the result from the previous task
    }
}, uiThread));

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