Using Custom Visual States - Page 4
       by kirupa  |  11 September 2009

In the previous page, you finished creating the states for your user control and learned what the C# syntax is for switching the states. In this page, I will explain how you can use an easier, codeless, and behavior-based solution instead.

The GoToStateAction
One of the built-in behaviors that comes with Expression Blend is the GoToStateAction. If you are not familiar with behaviors, please read my Using Behaviors tutorial first, for that will give you a detailed overview of the steps that I will be glossing through in this page.

First, make sure MainPage.xaml is open, and go ahead and display the Behaviors category in your Assets panel:

[ display your Behaviors category in your Assets panel ]

You should see the GoToStateAction present, so go ahead and drag / drop your GoToStateAction onto your checkbox by dropping it on either the object tree or on the artboard:

[ the GoToStateAction needs to live on your checkbox ]

Once you have dropped your behavior onto the Toggle Size checkbox, your Properties Inspector will display all of GoToStateAction's properties that are available for you to modify:

[ all of GoToStateAction's properties are displayed ]

Let's first talk about what we want to do. When the checkbox is checked, we want our user control to jump into its Large state. This means that, first, we need to modify the trigger. In the Trigger category, the EventName is set to Click, and we do not want that. Instead, the EventName needs to be Checked because we want this behavior to become active when the checkbox (this behavior's parent) becomes Active.

To change the EventName, simply click on the EventName drop-down and select Checked from the list:

[ change the EventName to Checked ]

Once you have selected the Checked event, your behavior will only become active when the checkbox is checked. Great!

Next, we want to specify the Large state to become active when this behavior becomes active. That is done in the series of properties listed under Common Properties:

[ next up, Common Properties ]

First, let's change the value of our TargetName. Our behavior currently resides on the ComboBox, and we want to target our ColorfulRectangle usercontrol where our states live. To do this, click on the little bullseye icon found to the right of the TargetName field and select our usercontrol that lives on the artboard:

[ we need to pick the element our states live on ]

Once you have done this, your TargetName field will now display the ColorfulRectangle user control. More specifically, it will display a named version of your ColorfulRectangle user control because you cannot target an unnamed element:

[ if you target an unnamed element, the element will be named for you ]

Once you've targeted the usercontrol you want, click on the StateName drop-down just below the TargetName property. Notice that you see the two states that you created earlier inside your ColorfulRectangle usercontrol. Go ahead and select the Large state:

[ select the Large state from the StateName drop-down ]

After you have selected the Large state, go ahead and test your application by pressing F5. Notice what happens when you check your Toggle SIze checkbox. You transition into your colorfulRectangle's Large state.

When you uncheck the checkbox, nothing happens. That is because your application doesn't know that is your intention, but it is very to fix that. Drag and drop another GoToStateAction onto your checkbox. This time, set the EventName to Unchecked to indicate that you want this behavior to become active when your checkbox is unchecked:

[ select the Unchecked event ]

You are almost done. All that is left is to set your TargetName to your colorfulRectangle UserControl, and set your StateName to Small. Your GoToStateAction's properties are going to look like as follows:

[ all of the properties have now been set! ]

If you run your application now, when your Toggle Size checkbox is checked or unchecked, the appropriate state will become active. That's all there is to it!

Conclusion
All of the built-in controls in Silverlight use the states functionality to define their custom look that becomes active depending on what you are doing with them. Fortunately, this functionality is quite extensible where you can create your own usercontrol and define your own states. Defining the states is only one part of the equation. The other part is actually making that state active, and in this tutorial, I presented two ways of doing that.

One way is by writing some simple C# code that allows you to switch states. The other way, my preferred way, is to use the GoToStateAction behavior that you get out of the box with Expression Blend 3. By using a behavior for changing states, you have a very visual way of specifying when this state will go active, which usercontrol this state lives on, and which state you want played.

If you are curious to see my final implementation of all this, feel free to download the source files from below:

Download Source Files

Got a question or just want to chat? Comment below or drop by our forums (they are actually the same thing!) where a bunch of the friendliest people you'll ever run into will be happy to help you out!

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