ConditionRacer ConditionRacer - 1 year ago 478
C# Question

WPF MessageBox with MVVM pattern?

Say I want to display some validation error to the user. In the MVVM pattern, I could have a label that is bound to some property on my viewmodel. But what if I wanted to show a message box while strictly adhering to the MVVM pattern. What would my viewmodel bind to, and how would it trigger a message box to be created/displayed?

Answer Source

Have an interface IMessageBoxService as:

interface IMessageBoxService
    bool ShowMessage(string text, string caption, MessageType messageType);

Create a WPFMessageBoxService class:

using System.Windows;

class WPFMessageBoxService : IMessageBoxService
    bool ShowMessage(string text, string caption, MessageType messageType)
        // TODO: Choose MessageBoxButton and MessageBoxImage based on MessageType received
        MessageBox.Show(text, caption, MessageBoxButton.OK, MessageBoxImage.Information);

In your ViewModel accept IMessageBoxService as a constructor parameter and inject WPFMessageBoxService using DI/IoC.

In the ViewModel, use IMessageBoxService.ShowMessage to show the MessageBox.

ShowMessageCommand = new DelegateCommand (
    () => messageBoxService.ShowMessage(message, header, MessageType.Information)

Customize IMessageBoxService interface to your needs, and pick up a better name.

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