Menus & Popovers - Learn SpriteBuilder for iOS Game Development - page 193

Adding a Callbacks Keyframe
Before resuming the game, it is a good idea to first remove the pause popover menu with
an animation. This gives the user some time to prepare herself for resuming play, perhaps
introducing a 3..2..1 countdown timer after dismissing the pause menu.
Now, theoretically, you could assign an animationManager.delegate and imple-
ment the completedAnimationSequenceNamed: method to find out if the resume
game Timeline is done playing.
However, I haven't explained how to use the Callbacks keyframes in the Timeline, and I
haven't explained how they can be used to run custom selectors at any point in the
Timeline. This situation is a good use for a Callbacks keyframe. In fact, any time you
need to call a selector at a specific point in time during a Timeline animation, you would
use a Callbacks keyframe.
In SpriteBuilder, open the PauseMenuLayer.ccb . Left-click on the Timeline List (see Fig-
ure 5-1 ) , and select New Timeline . This will create and select a new timeline named Un-
titled Timeline . Left-click the Timeline List again, and then select Edit Timelines to bring
up the same Timelines editing dialog as shown in Figure 5-9 . Double-click the Untitled
Timeline text to edit it, and rename this Timeline resume game . Leave the Autoplay check
box unchecked for the resume game Timeline, and then click Done .
Caution Once you have more than one timeline in a CCB, it becomes crucial
to verify that you are editing the correct Timeline. Check the Timeline List be-
fore making edits, especially if you're wondering why an edit wouldn't change
anything. It may take some time to get used to the idea of switching Timelines,
which you can do by left-clicking the Timeline List , and then select the desired
Timeline from the Timelines submenu.
Next, edit the Timeline duration by clicking on the digits box in the upper right corner of
the Timeline. (See Figure 5-2 for reference.) Make the Timeline two seconds long; this
should be enough time. Now move the Timeline Cursor to the end of the timeline at the
2-seconds mark. Here's where you should add a Callbacks keyframe.
If you tried to add a Callbacks keyframe before you probably couldn't. The trick is to hold
the Option key, and then click on the Callbacks segment to add a Callbacks keyframe.
With a Callbacks keyframe added, it still won't do anything yet—you'll have to edit the
keyframe's properties. To do so, double-click the keyframe. A popover like the one shown