Unable to close modal dialog with attached property (MVVM)? - wpf

Question

A newbie question, but I can't get it to work. In trying to use the answer to SO "How Should the View Model Close the form"
, I have a UserControl defined with:
<UserControl
.....
h:DialogCloser.DialogResult="{Binding DialogResult}"
>
which while designing shows:
Property 'DialogResult' is not attachable to elements of type 'UserControl'.
The DialogCloser is defined as:
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);
}
}
The UserControl is opened by:
var win = new WindowDialog();
win.Title = title;
win.DataContext = datacontext;
return win.ShowDialog();
In the View Model for the UserControl, I have:
public new void DoExit()
{
DialogResult = true;
}
private bool? dialogresult;
public bool? DialogResult
{
get
{
return dialogresult;
}
set
{
if (dialogresult != value)
{
dialogresult = value;
OnPropertyChanged("DialogResult");
}
}
}
When using DoExit(), the modal dialog, my UserControl, does not close. What's wrong? And how do I get the designer (VS 2010) to not throw error?
Thanks is advance for any help.
Addendum:
public class ModalDialogService : IModalDialogService
{
public bool? ShowDialog(string title, object datacontext)
{
var win = new WindowDialog();
win.Title = title;
win.DataContext = datacontext;
return win.ShowDialog();
}
}
Note: If the "UserControl" is rather made as a "Window", the designer is happy, but then the error is:
"Window must be the root of the tree. Cannot add Window as a child of Visual."
Help somebody?

Answer 1

I am new to this, but putting everything together, I would suggest this as a possible answer for newbies like myself.
Does this comply with best MVVM practices?
First, as the designer stated "Property 'DialogResult' is not attachable to elements of type 'UserControl'.
My translation, a "control" is not a window--so it can't be closed. Therefore,
h:DialogCloser.DialogResult="{Binding DialogResult}"
is wrong. Remove it.
Second, my usercontrol is being displayed as the sole element of an otherwise plain window as
<Window x:Class="Nova5.UI.Views.Ink.WindowDialog"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="WindowDialog"
WindowStyle="SingleBorderWindow"
WindowStartupLocation="CenterOwner" SizeToContent="WidthAndHeight">
<ContentPresenter x:Name="DialogPresenter" Content="{Binding .}"/>
</Window>
Now, the whole thing is initiated when the top most view model does
var dialog = new WindowDialog
{
Title = "It's me Margaret",
ShowInTaskbar = false,
Topmost = true,
ResizeMode = ResizeMode.NoResize
};
dialog.Owner = Application.Current.Windows.OfType<Window>().SingleOrDefault(x => x.IsActive);
ModalDialogService dialogService = new ModalDialogService();
dialogService.ShowDialog<PrescriptionWriterViewModel>(dialog,
new PrescriptionWriterViewModel(),
returnedViewModelInstance =>
{
if (dialog.DialogResult.HasValue && dialog.DialogResult.Value)
{
}
}
);
};
When Exit is clicked on the usercontrol, it performs by way of a DelegateCommand in its view model
public new void DoExit()
{
OnRequestClose();
}
public event EventHandler RequestClose;
void OnRequestClose()
{
EventHandler handler = this.RequestClose;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
This request to close is then handled in the initiating dialog service,
public void ShowDialog<TDialogViewModel>(IModalWindow view, TDialogViewModel viewModel, Action<TDialogViewModel> onDialogClose)
{
view.DataContext = viewModel;
IDialogViewModel vm = viewModel as IDialogViewModel;
if (vm !=null)
vm.RequestClose += (s,e)=> view.Close(); //RequestClose is the event in the ViewModel that the view will listen for.
if (onDialogClose != null)
{
view.Closed += (sender, e) => onDialogClose(viewModel);
}
view.Show();
}
When the view is closed, the onDialogClose(viewModel), then calls back to the topmost view model and completes the action specified with
returnedViewModelInstance =>
{
if (dialog.DialogResult.HasValue && dialog.DialogResult.Value)
{
}
}
So completes several intense hours of learning. I hope it is of use to somebody.