Good or bad practise for Dialogs in wpf with MVVM?

Question

hi, i lately had the problem of creating add and edit dialogs for my wpf app. all i want to do in my code was something like this. (I mostly use viewmodel first approach with mvvm)

ViewModel which calls a dialog window:

 var result = this.uiDialogService.ShowDialog("Dialogwindow title goes here", dialogwindowVM);

 ... do anything with the dialog result...

how does it works?

first i created a dialogservice

public interface IUIWindowDialogService
{
    bool? ShowDialog(string titel, object datacontext);
}

public class WpfUIWindowDialogService : IUIWindowDialogService
{
    public bool? ShowDialog(string titel, object datacontext)
    {
        var win = new WindowDialog();
        win.Title = titel;
        win.DataContext = datacontext;

        return win.ShowDialog();
    }

}

WindowDialog is a specail but simple window. i need it to hold my content:

<Window x:Class="WindowDialog"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    Title="WindowDialog" 
    WindowStyle="SingleBorderWindow" 
    WindowStartupLocation="CenterOwner" SizeToContent="WidthAndHeight">
    <ContentPresenter x:Name="DialogPresenter" Content="{Binding .}">

    </ContentPresenter>
</Window>

a problem with dialogs in wpf is the dialogresult=true. this can only achieve in code. thats why i created an interface for my dialogviewmodel to implement.

public interface IDialogResultVMHelper
{
    event EventHandler DialogResultTrueEvent;
}

when ever my viewmodel think its time for dialogresult=true, then raise this event :)

for my WindowDialog this means register to this event:

public partial class WindowDialog : Window
{
    public WindowDialog()
    {
        InitializeComponent();
        this.DialogPresenter.DataContextChanged += DialogPresenterDataContextChanged;
    }

    private void DialogPresenterDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
        var d = e.NewValue as IDialogResultVMHelper;

        if(d == null)
            return;

        d.DialogResultTrueEvent += DialogResultTrueEvent;
    }

    private void DialogResultTrueEvent(object sender, EventArgs e)
    {
        this.DialogResult = true;
    }
}

now at least i have to create an datatemplate in my resource file(app.xaml or something)

<DataTemplate DataType="{x:Type DialogViewModel:EditOrNewAuswahlItemVM}" >
        <DialogView:EditOrNewAuswahlItem/>
</DataTemplate>

well thats all, i can now call dialogs from my viewmodels:

 var result = this.uiDialogService.ShowDialog("Dialogwindow title goes here", dialogwindowVM);

now my question, do you see any problems with this solution?

Answer 1

This is a good approach and I used similar ones in the past. Go for it!

One minor thing I'd definitely do is make the event receive a boolean for when you need to set "false" in the DialogResult.

event EventHandler<bool> RequestCloseDialog;

Answer 2

I've been using an almost identical approach for several months now, and I'm very happy with it (i.e. I haven't yet felt the urge to rewrite it completely...)

In my implementation, I use a IDialogViewModel that exposes things such as the title, the standad buttons to show (in order to have a consistent apparence across all dialogs), a RequestClose dialog, and a few other things to be able to control the window size and behavior

Answer 3

You might be interested in the ViewModel sample application of the WPF Application Framework (WAF). It shows an alternative approach for showing dialog windows in a MVVM application.