LibGDX平台相关代码

关于Interfacing with platform specific code的译文

这是一个关于这个问题的论坛讨论，还包括iOS的具体内容。

有时，有必要访问平台特定的API，例如添加由诸如Swarm的框架提供的排行榜功能或者广告服务集成。

以下示例假定我们仅在Android上实现非常简单的排行榜API。 对于其他目标平台，我们只需要记录调用或提供模拟返回值。

Android API如下所示：

/** Let's assume this is the API provided by Swarm **/
public class LeaderboardServiceApi {
   public void submitScore(String user, int score) { ... }
}

第一步是以接口的形式创建API的抽象。该接口被放入核心项目中:

public interface Leaderboard {
   public void submitScore(String user, int score);
}

接下来，我们为每个平台创建具体的实现，并将它们放入各自的项目中。Android项目：

/** Android implementation, can access LeaderboardServiceApi directly **/
public class AndroidLeaderboard implements Leaderboard {
   private final LeaderboardServiceApi service;

   public AndroidLeaderboard() {
      // Assuming we can instantiate it like this
      service = new LeaderboardServiceApi();
   }

   public void submitScore(String user, int score) {
      service.submitScore(user, score);
   }
}

桌面项目

/** Desktop implementation, we simply log invocations **/
public class DesktopLeaderboard implements Leaderboard {
   public void submitScore(String user, int score) {
      Gdx.app.log("DesktopLeaderboard", "would have submitted score for user " + user + ": " + score);
   }
}

HTML5项目：

/** Html5 implementation, same as DesktopLeaderboard **/
public class Html5Leaderboard implements Leaderboard {
   public void submitScore(String user, int score) {
      Gdx.app.log("Html5Leaderboard", "would have submitted score for user " + user + ": " + score);
   }
}

接下来，ApplicationListener获取一个构造函数，我们可以通过它来传递具体的Leaderboard实现：

public class MyGame implements ApplicationListener {
   private final Leaderboard leaderboard;

   public MyGame(Leaderboard leaderboard) {
      this.leaderboard = leaderboard;
   }

   // rest omitted for clarity
}

在每个启动类中，我们然后简单地实例化MyGame，将相应的Leaderboard实现作为参数传递，例如在桌面上：

public static void main(String[] argv) {
   LwjglApplicationConfiguration config = new LwjglApplicationConfiguration();
   new LwjglApplication(new MyGame(new DesktopLeaderboard()), config);
}