Behavior to show a MessageBox from a ViewModel - Init

<body> <h1>Behavior to show a MessageBox from a ViewModel</h1> <p><a href="http://feedads.g.doubleclick.net/~a/-SzpVIQY9TwxqGParA5E4nLi9oE/0/da"><img src="http://feedads.g.doubleclick.net/~a/-SzpVIQY9TwxqGParA5E4nLi9oE/0/di" border="0" ismap="true"></img></a><br/> <a href="http://feedads.g.doubleclick.net/~a/-SzpVIQY9TwxqGParA5E4nLi9oE/1/da"><img src="http://feedads.g.doubleclick.net/~a/-SzpVIQY9TwxqGParA5E4nLi9oE/1/di" border="0" ismap="true"></img></a></p><p>Since I am a very lazy programmer and I always want to register of define services and whatnot I created this extreme, very simple behavior for showing a MessageBox from a ViewModel. I wrote the code for <a href="http://www.microsoft.com/windowsphone/" target="_blank"><a href="http://www.microsoft.com/windowsphone/" target="_blank">Windows Phone 7</a>,</a> but I suppose it could be used in Silverlight as well.</p> <p>The behavior itself is as simple as this:</p><pre>using System.Windows; using System.Windows.Interactivity; namespace Wp7nl.Behaviors { public class MessageBoxDisplayBehavior : Behavior<FrameworkElement> { public const string MessagePropertyName = "Message"; public string Message { get { return (string)GetValue(MessageProperty); } set { SetValue(MessageProperty, value); } } public static readonly DependencyProperty MessageProperty = DependencyProperty.Register( MessagePropertyName, typeof(string), typeof(MessageBoxDisplayBehavior), new PropertyMetadata(string.Empty, MessageChanged)); public static void MessageChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { var msg = e.NewValue as string; if (!string.IsNullOrEmpty(msg)) { MessageBox.Show(msg); } } } }</pre> <p>Easiest thing to use it is to just plonk it on any control in your Page using Blend, as long as it has the right datacontext, and select a string property to bind it to. In XAML, it usage looks something like this:</p><pre><Grid DataContext="{Binding ChooserViewModel}"> <i:Interaction.Behaviors> <Wp7nl_Behaviors:MessageBoxDisplayBehavior Message="{Binding MessageBoxMessage, Mode=TwoWay}"/> </i:Interaction.Behaviors> </pre> <p>Just one the one thing you might want to consider is how you define “MessageBoxMessage” in your ViewModel. I defined it as follows:</p><pre>private string messageBoxMessage; public string MessageBoxMessage { get { return messageBoxMessage; } set { messageBoxMessage = value; RaisePropertyChanged(() => MessageBoxMessage); } }</pre>as opposed to what you would normally do, which is<pre>private string messageBoxMessage; public string MessageBoxMessage { get { return messageBoxMessage; } set { <font color="#ff0000"> if (messageBoxMessage != value) {</font> messageBoxMessage = value; RaisePropertyChanged(() => MessageBoxMessage); <font color="#ff0000"> }</font> } }</pre>Intentionally left out the value check (in red), so RaisePropertyChanged always fires. This gives the real stupid user that makes the same error multiple times also multiple message boxes ;-) <div class="blogger-post-footer"><img width='1' height='1' src='https://blogger.googleusercontent.com/tracker/5295746446529817470-5806857015474792435?l=dotnetbyexample.blogspot.com' alt='' /></div><img src="http://feeds.feedburner.com/~r/blogspot/dotnetbyexample/~4/CeeTJkTxo0w" height="1" width="1"/> </body>