Building a Simple Windows Phone App - Page 6
       by kirupa  |  10 May 2010

In the previous page, you almost finished the application. You used a behavior to play the storyboard that resets your rectangle’s position when you release the drag. In this page, we’re just going to add the icing on this cake before wrapping things up.

Adding an Easing Function
To make our animation more realistic, one thing that we want to do is have our rectangle accelerate and bounce a bit when it returns to its original position. You have several ways of doing that, but the easiest and most direct way is by using an easing function that alters your animation.

Note - Optional Further Reading  
To learn more about easing functions, check out my earlier Easing Functions in Blend tutorial.

Because we will adding the easing function to the animation, go ahead and open the ResetPosition Storyboard that you created earlier. Click on the Storyboard drop-down from your Objects and Timeline panel, and from the menu that appears, select the ResetPosition storyboard:

[ from the Storyboard drop-down, select your ResetPosition storyboard ]

Once you have selected the ResetPosition storyboard, you will be back in the Timeline Recording mode that you were in earlier.
From your Timeline, select the keyframe that exists at the .5 second mark in the row your rectangle lives:

[ select your rectangle's keyframe at the .5 second mark ]

When you select the keyframe, your Properties Inspector will display some properties you can set to adjust the transition between the current keyframe and the previous keyframe:

[ your keyframe exposes some properties that you can edit ]

The property that we are most interested in is the EasingFunction editor which should have been selected for your already. From this editor, click on the EasingFunction drop-down and select the Back Out easing function:

[ select the Back Out easing function ]

Once you have selected the Back Out easing function, hit F5 again to preview your application. This time around, notice what happens when you drag your rectangle and release it.

Unlike before, when the rectangle would just animate back linearly, you’ll notice that your rectangle now snaps back into its position with a quick bounce!

Conclusion
Phew - you have now reached the end of this tutorial! We covered a lot of ground in this tutorial, so it seems fit to quickly review everything you have done.

Here is what we set out to create:

The first thing we did was draw a rectangle and customize it. We inserted a rectangle with a default size and location and quickly made it look different - nicer if you will!

For making the rectangle actually draggable, you applied a behavior that took care of all of the messy details. You simply dropped the behavior (MouseDragElementBehavior) onto the rectangle, and your rectangle automatically received draggable properties. That's the way behaviors roll.

At this point, your application is half-way done. What is remaining is the animation that brings your rectangle back after you are done dragging it around. To do this, we created a storyboard with a duration of .5 seconds that interacted with the TranslateX and TranslateY properties that corresponded to the position of the rectangle as it was being dragged around.

You then used another behavior called ControlStoryboardAction to cause the storyboard you created to play when you release the drag on the rectangle.

The last thing you did was tweak the animation a bit. While, by default, your animation progresses linearly, you can alter this behavior using easing functions. To give the rectangle the bounce and snap back effect, we set a Bounce Out easing function on the keyframe that makes up the animation.

And with that, you are done! If you want to see how my version of this example looks like, download the source files below:

Download Source Files

If you have a question about this or any other topic, the easiest thing is to comment below or drop by our forums where a bunch of the friendliest people you'll ever run into will be happy to help you out!

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