Show dialog with MVVM Light toolkit

dialogmvvmmvvm-light

I have a ViewModel that needs to show a modal window (using ShowDialog()) on a button click. The ViewModel catches the click command, but I don't want to do window.ShowDialog() within my ViewModel. I know there is a DialogMessage in MVVM Light, but that is used to show message boxes, not WPF modal windows.

Any ideas on how to do this?

Best Answer

You should use Messenger class. On the View register a message to show window, and then when you need to show it call Send method of Messenger class.

You can do something like this:

    //do this in the code-behind file of your View
    Messenger.Default.Register<string>(this, ShowWindow);
    
    private void ShowWindow(string message)
    {
        // your logic here
    }
    
    // In the ViewModel
    Messenger.Default.Send(“Some text”);

Related Solutions

.net – Handling Dialogs in WPF with MVVM

I suggest forgoing the 1990's modal dialogs and instead implementing a control as an overlay (canvas+absolute positioning) with visibility tied to a boolean back in the VM. Closer to an ajax type control.

This is very useful:

<BooleanToVisibilityConverter x:Key="booltoVis" />

as in:

<my:ErrorControl Visibility="{Binding Path=ThereWasAnError, Mode=TwoWay, Converter={StaticResource booltoVis}, UpdateSourceTrigger=PropertyChanged}"/>

Here's how I have one implemented as a user control. Clicking on the 'x' closes the control in a line of code in the usercontrol's code behind. (Since I have my Views in an .exe and ViewModels in a dll, I don't feel bad about code that manipulates UI.)

Wpf dialog

C# – How should the ViewModel close the form

I was inspired by Thejuan's answer to write a simpler attached property. No styles, no triggers; instead, you can just do this:

<Window ...
        xmlns:xc="clr-namespace:ExCastle.Wpf"
        xc:DialogCloser.DialogResult="{Binding DialogResult}">

This is almost as clean as if the WPF team had gotten it right and made DialogResult a dependency property in the first place. Just put a bool? DialogResult property on your ViewModel and implement INotifyPropertyChanged, and voilà, your ViewModel can close the Window (and set its DialogResult) just by setting a property. MVVM as it should be.

Here's the code for DialogCloser:

using System.Windows;

namespace ExCastle.Wpf
{
    public static class DialogCloser
    {
        public static readonly DependencyProperty DialogResultProperty =
            DependencyProperty.RegisterAttached(
                "DialogResult",
                typeof(bool?),
                typeof(DialogCloser),
                new PropertyMetadata(DialogResultChanged));

        private static void DialogResultChanged(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e)
        {
            var window = d as Window;
            if (window != null)
                window.DialogResult = e.NewValue as bool?;
        }
        public static void SetDialogResult(Window target, bool? value)
        {
            target.SetValue(DialogResultProperty, value);
        }
    }
}

I've also posted this on my blog.

Best Answer

Related Solutions

.net – Handling Dialogs in WPF with MVVM

C# – How should the ViewModel close the form

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