Recipe 6.7. Loading and Interacting with External Movies
ProblemYou want to load, and be able to interact with, an external .swf movie into your own movie. SolutionUse the new Loader class to load the .swf file, and then access the .swf file via the content property of the Loader instance. DiscussionRecipe 6.6 demonstrates how to load external images via the Loader class. Loading external .swf movies uses the same techniqueby calling the load( ) method on a Loader instance and passing a URL to a .swf instead of an image, the .swf is loaded into the movie. If the Loader is in the main display hierarchy, the .swf also appears on-screen. This recipe involves creating two separate .swf files, ExternalMovie.swf and LoaderExample.swf. The first movie, ExternalMovie.swf, will be loaded at runtime into the second movie, LoaderExample.swf. The code for ExternalMovie.swf is as follows: package { import flash.display.Sprite; import flash.display.Shape; public class ExternalMovie extends Sprite { private var _color:uint = 0x000000; private var _circle:Shape; public function ExternalMovie( ) { updateDisplay( ); } private function updateDisplay( ):void { // If the circle hasn't been created yet, create it // and make it visible by adding it to the display list if ( _circle == null ) { _circle = new Shape( ); addChild( _circle ); } // Clear any previously drawn content and draw // a new circle with the fill color _circle.graphics.clear( ); _circle.graphics.beginFill( _color ); _circle.graphics.drawCircle( 100, 100, 40 ); } // Changes the color of the circle public function setColor( color:uint ):void { _color = color; updateDisplay( ); } // Gets the current circle color value public function getColor( ):uint { return _color; } } }The code for ExternalMovie.swf is nothing out of the ordinarya black circle is created when the movie is executed. The main thing to notice about the code is that there are two public methods for accessing and modifying the color of the circle, getColor( ) and setColor( ). Whenever the setColor( ) method is invoked, the circle is redrawn with the updated color value. By declaring these methods as public, the methods are able to be called from a movie that loads the ExternalMovie.swf in at runtime. In contrast, the private updateDisplay( ) method won't be available to the loading movie. See Recipe 1.13 for more information about the visibility modifiers for methods. Now that ExternalMovie.swf is created, a new .swf needs to be created to load the external movie. This is done with LoaderExample.swf, which has the following code: package { import flash.display.*; import flash.net.URLRequest; import flash.events.Event; public class LoaderExample extends Sprite { private var _loader:Loader; public function LoaderExample( ) { // Create the Loader and add it to the display list _loader = new Loader( ); addChild( _loader ); // Add the event handler to interact with the loaded movie _loader.contentLoaderInfo.addEventListener( Event.INIT, handleInit ); // Load the external movie _loader.load( new URLRequest( "ExternalMovie.swf" ) ); } // Event handler called when the externally loaded movie is // ready to be interacted with private function handleInit( event:Event ):void { // Typed as * here because the type is not known at compile-time. var movie:* = _loader.content; // Calls a method in the external movie to get data out // Displays: 0 trace( movie.getColor( ) ); // Calls a method in the external movie to set data. // Sets the color in the external movie, which draws // a circle with the new color, in this case red movie.setColor( 0xFF0000 ); } } }The code for LoaderExample.swf is more interesting in that it communicates with the loaded movie. There are two main aspects in the preceding code:
The init event is fired when the loaded movie has initialized enough that its methods and properties are available to be interacted with. The movie can be controlled only after the init event has been fired from the loader. Attempting to interact with a loaded movie before it has initialized will generate runtime errors. To control the loaded movie, you'll first need to get a reference to it. This is done via the content property of the Loader class. In the preceding code, the loader variable refers to the Loader that pulled in the external .swf file, so you can access the movie via loader.content. If the loader variable weren't available, the event.target.content path could be used instead to get to the contents of the Loader. This is because event.target refers to the instance that generated the event, which is the same instance that the loader variable refers to. The content property is read-only, and returns an object of type DisplayObject. In the LoaderExample.swf code, you'll notice that instead of typing the movie variable as a DisplayObject, the same type as what the content property returns, the * type was used. This is necessary because trying to call the getColor( ) or setColor( ) methods on the movie reference generates compile-time errors if movie is typed as a DisplayObject. The movie being loaded, ExternalMovie.swf, has two public methods available for interaction. These methods are not part of the DisplayObject class; therefore, trying to call one of the methods from a variable of type DisplayObject is an error. The * type allows you to call any method that you'd like on the loaded movie. If the method does not exist in the loaded movie, a ReferenceError is thrown during execution. The getColor( ) method returns the color of the circle in ExternalMovie.swf to LoaderExample.swf. The LoaderExample.swf reports the color as 0, which is the same as 0x000000, or the color black. The setColor( ) method allows LoaderExample.swf to change the color of the circle drawn by ExternalMovie.swf. In this case, the color of the circle is set to red, and you can see that the ExternalMovie.swf updates the display after the new circle color value is set.
See AlsoRecipes 1.13 and 6.6 |
EAN: 2147483647
Pages: 351