/3/ clip event loops

the enterFrame event handler

• Timeline loops are effective but not necessarily elegant.
• In Flash 5 and later, we can use an enterFrame clip event handler to achieve the same result as a timeline loop.
• An enterFrame event handler causes a block of code to execute every time a frame passes in a movie.
• Let's recreate our timeline loop as an enterFrame event loop (we'll start with a movie, event-loop.fla, that already has a ball clip on Stage):

1. Select Insert>>New Symbol to create a blank movie clip symbol.
2. Name the clip symbol process.
3. Return to the main movie timeline and create a layer called processMove.
4. On the processMove layer, place an instance of the process symbol.
5. Select the process instance and attach the following code:
   onClipEvent (enterFrame) {
  _root.ball._x += 10;
}

make clip event loops more flexible

• The clip event example we just saw has a drawback: there's no way to programmatically start or stop the loop once it's started.
• We want to create an event loop that can be arbitrarily started and stopped.
• To do so, we create an empty clip that contains another empty clip with an enterFrame event loop.
• We then dynamically attach and remove the whole package whenever we want to start or stop the loop.
• Let's build a controllable event loop (event-loop-controllable.fla). Our movie already has a ball clip ready:

1. Select Insert>>New Symbol twice to create two blank movie clip symbols.
2. Name one clip symbol process, and the other eventLoop.
3. In the library, select the process clip, then select Options>>Linkage. The Symbol Linkage Properties dialog appears.
4. Select Export this symbol.
5. In the identifier box, type processMoveBall and then click OK.
6. On frame 1 of the process clip, place an instance of eventLoop.
7. Select the eventLoop instance, and attach the following code to it:
   
   onClipEvent (enterFrame) {
  _root.ball._x += 10;
}
8. Return to the main movie timeline and attach the following code to a "start move" button:
   on (release) {
  attachMovie("processMoveBall", "processMoveBall", 5000);
}
9. Attach the following code to a "stop move" button:
   on (release) {
  removeMovieClip(processMoveBall);
}