Implementing a blocking modal view/dialog like in Windows Forms - is it possible?

In short:

I want to show a view or action sheet and only continue code execution after the user has dismissed the view / sheet. So: line one shows the view, line two reads some result variable.

In detail why I would need this:

I'm porting a Windows Forms application over to the iPad. The original implementation has a communication class which uses a web service to communicate with the server. It offers a couple of methods to get data. Conveniently it checks prior to each call if the user still has a valid connection or if he has to re-enter his password for security reasons. If the password is required, the .NET class shows a modal dialog which blocks any further code executio and if the password was entered, retries the last call it has made before showing the dialog.

Now using CocoaTouch I'm facing a problem. I replaced the code that shows the dialog with a UIActionSheet. Works great but code execution continues immediately, whereas in Windows Forms it is blocked (the next line in Windows Forms after showing the dialogs is to read the entered password from the dialog) until the dialog has been closed.

I tried a Thread.Sleep() until the user dismisses the UIActionSheet but the Thread.Sleep() also blocks the main loop and my view won't even be drawn.

The alternative I currently see is to change all methods in the already working class and give them a return value: if password required, handle it, then retry.

But this means that all over my code I will have to add t开发者_如何学编程hese checks because at any given moment the password might be needed. That's why it is nested in communication class in Windows Forms.

Any other ideas?

René

Yes, it is possible.

To do this, what you can do is to run the mainloop manually. I have not managed to stop the mainloop directly, so I instead run the mainloop for 0.5 seconds and wait until the user responds.

The following function shows how you could implement a modal query with the above approach:

int WaitForClick ()
{
    int clicked = -1;
    var x = new UIAlertView ("Title", "Message",  null, "Cancel", "OK", "Perhaps");
    x.Show ();
    bool done = false;
    x.Clicked += (sender, buttonArgs) => {
        Console.WriteLine ("User clicked on {0}", buttonArgs.ButtonIndex);
 clicked = buttonArgs.ButtonIndex;
    };    
    while (clicked == -1){
        NSRunLoop.Current.RunUntil (NSDate.FromTimeIntervalSinceNow (0.5));
        Console.WriteLine ("Waiting for another 0.5 seconds");
    }

    Console.WriteLine ("The user clicked {0}", clicked);
    return clicked;
}

I think this approach using async/await is much better, and doesn't suffer from freezing the app when rotating the device, or when the autoscrolling interferes and leaves you stuck in the RunUntil loop forever without the ability to click a button (at least these problems are easy to reproduce on iOS7).

Modal UIAlertView

Task<int> ShowModalAletViewAsync (string title, string message, params string[] buttons)
{
    var alertView = new UIAlertView (title, message,  null, null, buttons);
    alertView.Show ();
    var tsc = new TaskCompletionSource<int> ();

    alertView.Clicked += (sender, buttonArgs) => {
        Console.WriteLine ("User clicked on {0}", buttonArgs.ButtonIndex);      
        tsc.TrySetResult(buttonArgs.ButtonIndex);
    };    
    return tsc.Task;
}