How to have LevelLoader method 'ignore' undefined entities?

问题

I am using a method of loading an xml file into a game as a level very similar to this:

private void loadLevel(int levelID)
{
final SimpleLevelLoader levelLoader = new SimpleLevelLoader(vbom);

final FixtureDef FIXTURE_DEF = PhysicsFactory.createFixtureDef(0, 0.01f, 0.5f);

levelLoader.registerEntityLoader(new EntityLoader<SimpleLevelEntityLoaderData>(LevelConstants.TAG_LEVEL)
{
    public IEntity onLoadEntity(final String pEntityName, final IEntity pParent, final Attributes pAttributes, final SimpleLevelEntityLoaderData pSimpleLevelEntityLoaderData) throws IOException 
    {
        final int width = SAXUtils.getIntAttributeOrThrow(pAttributes, LevelConstants.TAG_LEVEL_ATTRIBUTE_WIDTH);
        final int height = SAXUtils.getIntAttributeOrThrow(pAttributes, LevelConstants.TAG_LEVEL_ATTRIBUTE_HEIGHT);

        // TODO later we will specify camera BOUNDS and create invisible walls
        // on the beginning and on the end of the level.

        return GameScene.this;
    }
});

levelLoader.registerEntityLoader(new EntityLoader<SimpleLevelEntityLoaderData>(TAG_ENTITY)
{
    public IEntity onLoadEntity(final String pEntityName, final IEntity pParent, final Attributes pAttributes, final SimpleLevelEntityLoaderData pSimpleLevelEntityLoaderData) throws IOException
    {
        final int x = SAXUtils.getIntAttributeOrThrow(pAttributes, TAG_ENTITY_ATTRIBUTE_X);
        final int y = SAXUtils.getIntAttributeOrThrow(pAttributes, TAG_ENTITY_ATTRIBUTE_Y);
        final String type = SAXUtils.getAttributeOrThrow(pAttributes, TAG_ENTITY_ATTRIBUTE_TYPE);

        final Sprite levelObject;

        if (type.equals(TAG_ENTITY_ATTRIBUTE_TYPE_VALUE_PLATFORM1))
        {
            levelObject = new Sprite(x, y, resourcesManager.platform1_region, vbom);
            PhysicsFactory.createBoxBody(physicsWorld, levelObject, BodyType.StaticBody, FIXTURE_DEF).setUserData("platform1");
        } 
        else if (type.equals(TAG_ENTITY_ATTRIBUTE_TYPE_VALUE_PLATFORM2))
        {
            levelObject = new Sprite(x, y, resourcesManager.platform2_region, vbom);
            final Body body = PhysicsFactory.createBoxBody(physicsWorld, levelObject, BodyType.StaticBody, FIXTURE_DEF);
            body.setUserData("platform2");
            physicsWorld.registerPhysicsConnector(new PhysicsConnector(levelObject, body, true, false));
        }
        else if (type.equals(TAG_ENTITY_ATTRIBUTE_TYPE_VALUE_PLATFORM3))
        {
            levelObject = new Sprite(x, y, resourcesManager.platform3_region, vbom);
            final Body body = PhysicsFactory.createBoxBody(physicsWorld, levelObject, BodyType.StaticBody, FIXTURE_DEF);
            body.setUserData("platform3");
            physicsWorld.registerPhysicsConnector(new PhysicsConnector(levelObject, body, true, false));
        }
        else if (type.equals(TAG_ENTITY_ATTRIBUTE_TYPE_VALUE_COIN))
        {
            levelObject = new Sprite(x, y, resourcesManager.coin_region, vbom)
            {
                @Override
                protected void onManagedUpdate(float pSecondsElapsed) 
                {
                    super.onManagedUpdate(pSecondsElapsed);

                    /** 
                     * TODO
                     * we will later check if player collide with this (coin)
                     * and if it does, we will increase score and hide coin
                     * it will be completed in next articles (after creating player code)
                     */
                }
            };
            levelObject.registerEntityModifier(new LoopEntityModifier(new ScaleModifier(1, 1, 1.3f)));
        }            
        else
        {
            throw new IllegalArgumentException();
        }

        levelObject.setCullingEnabled(true);

        return levelObject;
    }
});

levelLoader.loadLevelFromAsset(activity.getAssets(), "level/" + levelID + ".lvl");

}

If I add an entity with some random type string in my level XML file that is not defined in that method and I run it, I get this stacktrace:

05-02 16:56:40.880: E/AndroidRuntime(3665): FATAL EXCEPTION: UpdateThread
05-02 16:56:40.880: E/AndroidRuntime(3665): org.andengine.util.level.exception.LevelLoaderException: java.lang.IllegalArgumentException
05-02 16:56:40.880: E/AndroidRuntime(3665):     at org.andengine.util.level.LevelLoader.loadLevelFromStream(LevelLoader.java:127)
05-02 16:56:40.880: E/AndroidRuntime(3665):     at org.andengine.util.level.LevelLoader.loadLevelFromAsset(LevelLoader.java:97)
05-02 16:56:40.880: E/AndroidRuntime(3665):     at org.andengine.util.level.LevelLoader.loadLevelFromAsset(LevelLoader.java:88)
05-02 16:56:40.880: E/AndroidRuntime(3665):     at org.andengine.util.level.LevelLoader.loadLevelFromAsset(LevelLoader.java:82)
05-02 16:56:40.880: E/AndroidRuntime(3665):     at com.package.game.GameScene.loadLevel(GameScene.java:478)
05-02 16:56:40.880: E/AndroidRuntime(3665):     at com.package.game.GameScene.setLevel(GameScene.java:1693)
05-02 16:56:40.880: E/AndroidRuntime(3665):     at com.package.game.SceneManager$1.onTimePassed(SceneManager.java:117)
05-02 16:56:40.880: E/AndroidRuntime(3665):

I need to be able to load different entities at different time from one level file, so how can I modify this method somehow so that it just kind of "ignores" entities that are not defined?

回答1:

I have just looked in LevelParser.java method startElement(), you can bypass where the IllegalArgumentException exception is thrown in Andengine by creating a default Entity Loader. I.e.,

levelLoader.setDefaultEntityLoader( new IEntityLoader()
{

    @Override
    public void onLoadEntity(String pEntityName, Attributes pAttributes) {
        // TODO Auto-generated method stub
        Log.w("setDefaultEntityLoader","Unknown Entity");
    }

});

This default onLoadEntity() will then get called instead of the exception being raised. I tested it on GLES 1 and it works as expected.

Hope this helps.

来源：https://stackoverflow.com/questions/16376949/how-to-have-levelloader-method-ignore-undefined-entities

标签

java

android

xml

andengine