Event Handlers Applied (ActionScript: The Definitive Guide)

10.17. Event Handlers Applied

We'll conclude our exploration of ActionScript events and event handlers with a few real-world examples. These are simple applications, but they give us a sense of how flexible event-based programming can be. The last two examples are available for download from the online Code Depot.

Example 10-7 makes a clip shrink and grow.

Example 10-7. Oscillating the Size of a Movie Clip

onClipEvent (load) {
  var shrinking = false;
  var maxHeight = 300;
  var minHeight = 30;
}

onClipEvent (enterFrame) {
  if (_height < maxHeight && shrinking == false) {
    _height += 10;
    _width  += 10;
  } else {
    shrinking = true;
  }

  if (shrinking == true) {
    if (_height > minHeight) {
      _height -= 10;
      _width  -= 10;
    } else {
      shrinking = false;
      _height += 10;     // Increment here so we don't
      _width  += 10;     // miss a cycle
    }
  }
}

Example 10-8 simulates a custom mouse pointer by hiding the normal system pointer and making a clip follow the mouse location around the screen. In the example, the mouseDown and mouseUp handlers resize the custom pointer slightly to indicate mouseclicks.

Example 10-8. A Custom Mouse Pointer

onClipEvent (load) {
  Mouse.hide( );
}

onClipEvent (mouseMove) {
  _x = _root._xmouse;
  _ y = _root._ymouse;
  updateAfterEvent( );
}

onClipEvent (mouseDown) {
  _width  *= .5;
  _height *= .5;
  updateAfterEvent( );
}

onClipEvent (mouseUp) {
  _width  *= 2;
  _height *= 2;
  updateAfterEvent( );
}

Finally, simply to prove the power of the ActionScript movie clip event handlers, Example 10-9 turns a movie clip into a customized button using mouseMove to check for rollovers, mouseDown and mouseUp to check for button clicks, and the hitTest( ) function to make hit detection a snap. This example assumes that the clip with the handlers has three keyframes labeled up, down, and over (corresponding with the usual button states).

Example 10-9. A Movie Clip Button

onClipEvent (load) {
  stop( );
}

onClipEvent (mouseMove) {
  if (hitTest(_root._xmouse, _root._ymouse, true) && !buttonDown) {
    this.gotoAndStop("over");
  } else if (!hitTest(_root._xmouse, _root._ymouse, true) && !buttonDown) {
    this.gotoAndStop("up");
  }
  updateAfterEvent( );
}

onClipEvent (mouseDown) {
  if (hitTest(_root._xmouse, _root._ymouse, true)) {
    buttonDown = true;
    this.gotoAndStop("down");
  }
  updateAfterEvent( );
}

onClipEvent (mouseUp) {
  buttonDown = false;
  if (!hitTest(_root._xmouse, _root._ymouse, true)) {
    this.gotoAndStop("up");
  } else {
    this.gotoAndStop("over");
  }
  updateAfterEvent( );
}