[RFC] Support for CancellationToken to cancel dialogs

[thoemmi]

As a possible solution for #2018 I implemented support for CancellationToken to cancel dialogs.

I added a CancellationToken to MetroDialogSettings and the handling of that token to InputDialog, LoginDialog, MessageDialog, and ProgressDialog. ProgressDialog's implementation is different from the others in that it only sets ProgressDialogManager.IsCanceled to true.

Of course, users of MahApps.Metro deriving their dialogs from BaseMetroDialog have to implement their own handling of the cancellation.

Usage

var cancellationTokenSource = new CancellationTokenSource();

var mySettings = new MetroDialogSettings()
{
    // ...
    CancellationToken = cancellationTokenSource.Token
};

Here's an example using a timer to cancel the message box (by calling cancellationTokenSource.Cancel()) after 10 seconds:

DispatcherTimer timer = null;
timer = new DispatcherTimer(
    TimeSpan.FromSeconds(10),
    DispatcherPriority.DataBind,
    (o, args) => {
        timer.Stop();
        cancellationTokenSource.Cancel();
    },
    Dispatcher
    );
timer.Start();

MessageDialogResult result = await this.ShowMessageAsync("Hello", "Welcome to metro!",
    MessageDialogStyle.AffirmativeAndNegative, mySettings);

[punker76]

@thoemmi It's a nice solution, but I'm torn about this because it's a breaking change...

[thoemmi]

Why is it a breaking change? I added MetroDialogSettings.CancellationToken, but didn't change the existing functionality.

[punker76]

@thoemmi :-( my mistake, it's all fine with this.