Implementing ShowDialog() style functionality without disabling any other windows

I need a simple prompt window to ask the user to do something with an OK/Cancel return. But I also need all Windows to remain functional, so a xx.ShowDialog isn't appropriate.

This is my attempt. DialogWindow takes a Delegate in the constructor and calls it when OK or Cancel is clicked with a True/False parameter respectively. The Window is coded to take top Z priority.

It seems to work but I'm not very knowledgeable on await usage. Is there an easier way?

bool result;
        ManualResetEvent manualReset = new ManualResetEvent(false);
        DialogWindow myDialog = new DialogWindow((dialogResult) =>
        {
            result = dialogResult;
            manualReset.Set();
        });
        myDialog.Show();
        await Task.Factory.StartNew(() =>
        {
            manualReset.WaitOne();
        });
        //Do something with result

Using ManualResetEvent this way means that you're blocking a thread unnecessarily while the dialog is shown. Instead, you should use TaskCompletionSource, which allows you to create a Task that completes when you want it to.

Encapsulated into a method, the code could look something like this:

public static Task ShowAsync()
{
    var tcs = new TaskCompletionSource();
    var dialog = new DialogWindow(tcs.SetResult);
    dialog.Show();
    return tcs.Task;
}

StackExchange Code Review Q#65183, answer score: 4