Libgdx之Game场景切换Screen

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在实际开发中我们需要在不同的时候切换不同游戏场景，比如需要有游戏设置界面、有些菜单界面和游戏主界面。

Screen 游戏场景

在Libgdx中Screen代表了一个游戏场景，有点类似coco2d-x中的Scene，但是Screen不能独立存在，必须依靠Game来切换。

官方的注释： Screen代表了应用程序中众多的场景之一(Screens)，例如：主菜单，设置菜单，游戏场景等。Screen不会自动调用#dispose()方法

    /** Called when this screen becomes the current screen for a {@link Game}. 每次切换到此Screen都会调用*/
    public void show ();

    /** Called when the screen should render itself.
     * @param delta The time in seconds since the last render. */
    public void render (float delta);

    /** @see ApplicationListener#resize(int, int) */
    public void resize (int width, int height);

    /** @see ApplicationListener#pause() */
    public void pause ();

    /** @see ApplicationListener#resume() */
    public void resume ();

    /** Called when this screen is no longer the current screen for a {@link Game}. */
    public void hide ();

    /** Called when this screen should release all resources. */
    public void dispose ();

Game implements ApplicationListener

Game继承自ApplicationListener，同时也有游戏生存的生命周期。

    protected Screen screen;

    @Override
    public void dispose () {
        if (screen != null) screen.hide();
    }

    @Override
    public void pause () {
        if (screen != null) screen.pause();
    }

    @Override
    public void resume () {
        if (screen != null) screen.resume();
    }

    @Override
    public void render () {
        if (screen != null) screen.render(Gdx.graphics.getDeltaTime());
    }

    @Override
    public void resize (int width, int height) {
        if (screen != null) screen.resize(width, height);
    }

    /** Sets the current screen. {@link Screen#hide()} is called on any old screen, and {@link Screen#show()} is called on the new
     * screen, if any.
     * @param screen may be {@code null} */
    public void setScreen (Screen screen) {
        if (this.screen != null) this.screen.hide();
        this.screen = screen;
        if (this.screen != null) {
            this.screen.show();
            this.screen.resize(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        }
    }

    /** @return the currently active {@link Screen}. */
    public Screen getScreen () {
        return screen;
    }

通过上面代码可以看到在游戏dispose()时，实际上是调用的screen.hide()方法，同时在setScreen(Screen screen)时也是调用的screen.hide()方法，并没有看到有调用screen.dispose()方法。因此在实际开发过程中，我们要注意自己处理好Screen的内存，防止内存泄漏。