Behaviors in Blend 3
How to create a simple Behavior for Blend 3
Behaviors are a new feature in Blend/Silverlight 3 and WPF. They allow designers to handle user interactions in XAML, and they also provide a clean division of concerns. Unfortunately, in the Blend 3 Preview, there aren't any behaviors included. This guide shows you how to write a behavior from scratch and also gives a look at a great new behavior written by Laurent Bugnion.
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Important Code
Information From the Video
Behaviors Solve a Problem
Probably the biggest design issue with Blend 2/Silverlight 2 is that it's difficult to hanlde user interactions from the XAML. This means that designers have to drop into code (or hand off to developers) to handle user events. The handling of a button's "Click" event is an example of this.
public MainPage()
{
InitializeComponent();
OurButton.Click += (s, e) =>
{
//message box
};
}
Blend 3 Preview doesn't have default behaviors
They can either be downloaded separately (see the references section) or they can be written from scratch.
Adding a reference
In Blend 3 Preview, the .dll for Behaviors is stored in the Blend install directory (C:\Program Files\Microsoft Expression\Blend 3 Preview\Libraries)
Create Behavior
Create a class that inherits from TargetedTriggerAction.
public class PopupBehavior : Microsoft.Expression.Interactivity.TargetedTriggerAction<FrameworkElement>
{
}
Adding Functionality
Override the Invoke method to customize what the Behavior will do. In this case, the Behavior will simply show a message box.
public class PopupBehavior : Microsoft.Expression.Interactivity.TargetedTriggerAction<FrameworkElement>
{
protected override void Invoke(object parameter)
{
HtmlPage.Window.Alert(DisplayText);
}
}
Adding Properties
Allowing a designer to cusomtize a Behavior is as simple as adding a dependency property. Here, there is a vanilla dependency property wrapped by a CLR type.
public class PopupBehavior : Microsoft.Expression.Interactivity.TargetedTriggerAction<FrameworkElement>
{
public static readonly DependencyProperty DisplayTextProperty =
DependencyProperty.Register("DisplayText", typeof(string), typeof(PopupBehavior), null);
[Category("DisplayText")]
public string DisplayText
{
get { return (string)GetValue(DisplayTextProperty); }
set { SetValue(DisplayTextProperty, value); }
}
protected override void Invoke(object parameter)
{
HtmlPage.Window.Alert(DisplayText);
}
}
WPF Magnifying Behavior
Laurent Bugnion has created a really cool Behavior for WPF. It allows for the creation of a "magnifying" glass. Any element can both be magnified and also become a magnifying glass! Using this Behavior is super simple, and there's a link to his article and the code in the References section.
References
Jose is a fellow Silverlight MVP and gives a great overview of Behaviors in Blend 3.
This is a talk that covers Behaviors. There are some surprising things that Behaviors can accomplish. There's a link from here to some sample Behaviors that can be downloaded.
This is a great overview (no code) of the thinking behind Behaviors.
Laurent has implemented a WPF Magnifying Behavior. In this post, he provides the source and a sample application.
