How to await an event click [duplicate]

Answer 1

Here is an extension method you can use. Unsubscribing from the Click event is important to avoid memory leaks, because event publishers keep references of event subscribers.

public static Task OnClickAsync(this Control source)
{
    var tcs = new TaskCompletionSource<bool>();
    source.Click += OnClick;
    return tcs.Task;

    void OnClick(object sender, EventArgs e)
    {
        source.Click -= OnClick;
        tcs.SetResult(true);
    }
}

Usage example:

await Button1.OnClickAsync();

Answer 2

This is the fix for my initial code, that makes it work as expected. I had to define a closure for the callback

AsyncCallback callback;

Then I had to pass the callback to the closure from the beginMethod:

private IAsyncResult beginMethod(AsyncCallback callback, object state)
{
    this.callback = callback;
    return Task.FromResult(true);
}

and finally invoke it from the event (i.e. the Command method in the MVVM for WPF)

private async void RunNext()
{
    IsBusy = true;
    ProgressMessage = "Wait 10 seconds...";
    await workToDo();
    ProgressMessage = "Work done!";
    IsBusy = false;
    if (callback != null)
    {
        callback.Invoke(Task.FromResult(true));
    }
}

Answer 3

To await something, it needs to be a Task (this is an oversimplification, but that's the important part) _{(C# can await any object that exposes a TaskAwaiter GetAwaiter() method, but 95% of the time C# developers will be consuming Task/Task<T> objects).}.

To create a Task you use TaskCompletionSource. This is how you can create a Task representation around other conceptual "tasks", like the IAsyncResult-style APIs, threads, overlapped IO, and so on.

Assuming this is WinForms, then do this:

class MyForm : Form
{
    // Note that `TaskCompletionSource` must have a generic-type argument.
    // If you don't care about the result then use a dummy null `Object` or 1-byte `Boolean` value.
    private TaskCompletionSource<Button> tcs;

    private readonly Button button;

    public MyForm()
    {
        this.button = new Button() { Text = "Click me" };
        this.Controls.Add( this.button );
        this.button.Click += this.OnButtonClicked;
    }

    private void OnButtonClicked( Object sender, EventArgs e )
    {
        if( this.tcs == null ) return;

        this.tcs.SetResult( (Button)sender );
    }

    internal async Task BatchLogicAsync()
    {
        this.tcs = new TaskCompletionSource<Button>();

        ProgressMessage = "Batch Logic Starts";

        Button clickedButton = await this.tcs.Task;

        ProgressMessage = "Batch Logic Ends";
    }
}