Message box/dialog/pop-up approach in MVVM - wpf

Question

I want to find a way to implement different forms of modals in MVVM WPF application. Like dialogs with returning results, message boxes or modal sub-windows with some controls inside.
Can you give me an advice about an efficient and modern approach for it?

Answer 1

I rarely find much use for anything other than a confirmation request. "Do you really want to delete that?" kind of thing.
Things popping up and asking for extra input just aren't super useful in my experience.
To my mind though, what you're doing is splitting your code. There is code up to showing the dialog. There is then code happens if the user clicks OK or Yes or selects a thingummajig in the dialog.
I split these into separate pieces of code. So there is not necessarilly a need to stop code running. It's in a separate method ( or command ) which is only run if the user hits the right button.
My first approach uses a control which itself has no UI. It exists just to get something encapsulated into the view.
namespace UserInput
{
public class ConfirmationRequestor : Control, ICommandSource
{
public bool? ShowConfirmDialog
{
get
{
return (bool?)GetValue(ShowConfirmDialogProperty);
}
set
{
SetValue(ShowConfirmDialogProperty, value);
}
}
public static readonly DependencyProperty ShowConfirmDialogProperty =
DependencyProperty.Register("ShowConfirmDialog",
typeof(bool?),
typeof(ConfirmationRequestor),
new FrameworkPropertyMetadata(null
, new PropertyChangedCallback(ConfirmDialogChanged)
)
{ BindsTwoWayByDefault = true }
);
private static void ConfirmDialogChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if ((bool?)e.NewValue != true)
{
return;
}
ConfirmationRequestor cr = (ConfirmationRequestor)d;
Window parent = Window.GetWindow(cr) as Window;
MessageBoxResult result = MessageBox.Show(parent, cr.Message, cr.Caption, cr.MsgBoxButton, cr.MsgBoxImage);
if (result == MessageBoxResult.OK || result == MessageBoxResult.Yes)
{
if (cr.Command != null)
{
cr.Command.Execute(cr.CommandParameter);
}
}
cr.SetValue(ShowConfirmDialogProperty, false);
}
public MessageBoxButton MsgBoxButton
{
get { return (MessageBoxButton)GetValue(MsgBoxButtonProperty); }
set { SetValue(MsgBoxButtonProperty, value); }
}
public static readonly DependencyProperty MsgBoxButtonProperty =
DependencyProperty.Register("MsgBoxButton",
typeof(MessageBoxButton),
typeof(ConfirmationRequestor),
new PropertyMetadata(MessageBoxButton.OK));
public MessageBoxImage MsgBoxImage
{
get { return (MessageBoxImage)GetValue(MsgBoxImageProperty); }
set { SetValue(MsgBoxImageProperty, value); }
}
public static readonly DependencyProperty MsgBoxImageProperty =
DependencyProperty.Register("MsgBoxImage",
typeof(MessageBoxImage),
typeof(ConfirmationRequestor),
new PropertyMetadata(MessageBoxImage.Warning));
public string Caption
{
get { return (string)GetValue(CaptionProperty); }
set { SetValue(CaptionProperty, value); }
}
public static readonly DependencyProperty CaptionProperty =
DependencyProperty.Register("Caption",
typeof(string),
typeof(ConfirmationRequestor),
new PropertyMetadata(string.Empty));
public string Message
{
get { return (string)GetValue(MessageProperty); }
set { SetValue(MessageProperty, value); }
}
public static readonly DependencyProperty MessageProperty =
DependencyProperty.Register("Message",
typeof(string),
typeof(ConfirmationRequestor),
new PropertyMetadata(string.Empty));
public ICommand Command
{
get { return (ICommand)GetValue(CommandProperty); }
set { SetValue(CommandProperty, value); }
}
public static readonly DependencyProperty CommandProperty =
DependencyProperty.Register("Command", typeof(ICommand), typeof(ConfirmationRequestor), new UIPropertyMetadata(null));
public object CommandParameter
{
get { return (object)GetValue(CommandParameterProperty); }
set { SetValue(CommandParameterProperty, value); }
}
public static readonly DependencyProperty CommandParameterProperty =
DependencyProperty.Register("CommandParameter", typeof(object), typeof(ConfirmationRequestor), new UIPropertyMetadata(null));
public IInputElement CommandTarget
{
get { return (IInputElement)GetValue(CommandTargetProperty); }
set { SetValue(CommandTargetProperty, value); }
}
public static readonly DependencyProperty CommandTargetProperty =
DependencyProperty.Register("CommandTarget", typeof(IInputElement), typeof(ConfirmationRequestor), new UIPropertyMetadata(null));
}
}
I have a viewmodel designed to go with this which is exposed as a property on my window viewmodel. That viewmodel and the control encapsulate the confirmer functionality.
namespace UserInput
{
public class ConfirmationRequestorVM : INotifyPropertyChanged
{
private string caption;
public string Caption
{
get { return caption; }
set
{
caption = value;
NotifyPropertyChanged();
}
}
private string message;
public string Message
{
get { return message; }
set
{
message = value;
NotifyPropertyChanged();
}
}
private MessageBoxButton msgBoxButton;
public MessageBoxButton MsgBoxButton
{
get { return msgBoxButton; }
set
{
msgBoxButton = value;
NotifyPropertyChanged();
}
}
private MessageBoxImage msgBoxImage;
public MessageBoxImage MsgBoxImage
{
get { return msgBoxImage; }
set
{
msgBoxImage = value;
NotifyPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
Usage
In the relevant view
<input:ConfirmationRequestor
ShowConfirmDialog="{Binding ShowConfirmation, Mode=TwoWay}"
MsgBoxImage="{Binding confirmer.MsgBoxImage}"
MsgBoxButton="{Binding confirmer.MsgBoxButton}"
Message="{Binding confirmer.Message}"
Caption="{Binding confirmer.Caption}"
Command="{Binding OkCommand}"
/>
Most of that is fairly self explanatory.
When ShowConfirmation is set to true, that control will show a messagebox.
If the user clicks OK or Yes then the OkCommand will be executed.
Hence if you need deletion confirmation then you show your messagebox and the actual deletion would be in that OkCommand.
If you want more complicated UI then rather than using a messagebox at all you could show a window from similar control.
Let's call this a DialogueController. This could be rather simpler since we can rely on our own UI and bind commands.
This control would have a dependency property for view Type. This being the type of a usercontrol which needs to be shown.
Another bool dependency property and change handler would control showing the type.
When the showdialog bool becomes true.
A method instantiates a window ( or it could be a popup if you prefer ) instantiates a usercontrol of the type specified in our other DP. Sets the window datacontext to our current datacontext.
You could use getwindow to find the parent window and set that to parent of our new (dialogue) window instance.
Thus sharing the parent window viewmodel as datacontext.
Call showdialog on the window. Or you could just call show.
You then have whatever UI you wrote in your usercontrol shown in a window.
It has access to your parent window viewmodel so it can reference any of your data you need.
And... It's Yes or OK button can bind to whatever command you defined in that parent window viewmodel.
You could also do things like select from a list and bind selectedFoo in your parent window viewmodel as well.
If you don't showmodal then when you change shared properties anything bound in your parent window can get those changes.
Like I said though.
I've not really come across much demand for that sort of thing.
There are also some elephants in the not-dialog room.
A pop up referencing it's parent viewmodel.
And
An expander similarly.
And
Just overlaying a panel on top of everything inside your parent window. This is how I have done editing for data in datagrids in a number of apps.
The key thing I found was the realisation:
You can "just" split your code into code before the dialog. Show the dialog. Then the "doing" aspect of any dialog-like-UI can go in a separate command.
OK, it's not exactly a road to damascus moment. But it simplifies things. I like simple. More likely to work.