Explain how async waits again

Question

This is my event handler code:

protected async void TestrunSaveExecute()
{
    bool saveResult = await SaveTestRunAsync();
}

To maintain responsiveness of the user interface, I used the async/ method await.

In my understanding, now I can perform some lengthy operations in SaveTestRunAsync()without blocking the user interface, since it is decoupled using a keyword await.

private async Task<bool> SaveTestRunAsync()
{
    //System.Threading.Thread.Sleep(5000); --> this blocks the UI
    await Task.Delay(5000); // this doesn't block UI

    return true;
}

Could you explain why the call Thread.Sleepstill blocks the user interface, but Task.Delaynot?

Answer 1

The code still runs in the user interface thread.

It does not work in the background thread.

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