In Chapter 14, we covered the behaviors that manipulate layers (namely Drag Layer and Set Text of Layer). You can add other behaviors to a timeline, such as the Set Text of Status Bar behavior, which displays a message in the browser status bar, or the Show-Hide Layers behavior, which (surprise!) shows and hides layers .
Behaviors are added in the Timelines panel's Behaviors channel , indicated by the letter B in Figure 17-5.
Figure 17-5. A behavior in the Timelines panel
To add a behavior to a timeline, click a frame in the Behaviors channel of the Timelines panel and choose a behavior from the Behaviors panel's Add Behavior (+) pop-up menu. (You can also use Modify Timeline Add Behavior to Timeline, which opens the Behaviors panel for you). Timeline behaviors can be added in any frame of the timeline (in either keyframes or tween frames ).
To delete all behaviors attached to a frame, click the frame in the Behaviors channel of the Timelines panel and choose Modify Timeline Remove Behavior. To delete a single behavior when more than one is attached to the same frame, use the Remove Behavior (-) button in the Behaviors panel.
17.3.1 Show-Hide Layers Behavior
The most common behavior you'll use in a timeline is, not surprisingly, one that controls layer visibility. Applying the Show-Hide Layers behavior, using the Add Behavior (+) pop-up menu in the Behaviors panel, opens the Show-Hide Layers dialog box shown in Figure 17-6.
Figure 17-6. The Show-Hide Layers dialog box
The Show-Hide Layers dialog box lists all layers in the current document, not just those added to a timeline. The dialog box does not list images. To hide an image, insert it into a layer and then hide the layer. As seen in Figure 17-6, use the Show and Hide buttons to show or hide each layer. You can also leave layers at their default (current) setting. Add this behavior in the Behaviors channel of a timeline in the frame you want the change to occur. This same behavior can be attached to an HTML element, such as an image acting as a button, to show or hide layers under user control. It can be applied to the <body> tag to show or hide layers when the document loads.