.net – Handling Dialogs in WPF with MVVM


In the MVVM pattern for WPF, handling dialogs is one of the more complex operations. As your view model does not know anything about the view, dialog communication can be interesting. I can expose an ICommand that when the view invokes it, a dialog can appear.

Does anyone know of a good way to handle results from dialogs? I am speaking about windows dialogs such as MessageBox.

One of the ways we did this was have an event on the viewmodel that the view would subscribe to when a dialog was required.

public event EventHandler<MyDeleteArgs> RequiresDeleteDialog;

This is OK, but it means that the view requires code which is something I would like to stay away from.

Best Solution

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