Slick2D getGraphics（）返回null，發生空指針異常

Question

我正在努力讓我的slick2d遊戲呈現，但container.getGraphics（）返回null，我得到一個空指針異常。我查了一下，這是的getGraphics（），這是返回null使用：

if (container.getGraphics()==null) return; 

這種固定的NPE，但那麼當然我無法呈現任何內容。

堆棧跟蹤：

Tue Sep 02 21:42:19 MDT 2014 INFO:Slick Build #237 
Exception in thread "Thread-1" java.lang.NullPointerException 
    at com.nonuniversal.client.MenuState.render(MenuState.java:17) 
    at org.newdawn.slick.state.StateBasedGame.render(StateBasedGame.java:199) 
    at com.nonuniversal.client.Game.run(Game.java:33) 
    at java.lang.Thread.run(Unknown Source) 

請注意LunatopiaClient需要用戶名參數跑的時候......

import org.newdawn.slick.AppGameContainer; 
import org.newdawn.slick.SlickException; 

public class LunatopiaClient{ 
    private String username; 
    AppGameContainer container; 
    Game game; 

    public LunatopiaClient(String username) { 

     this.username = username; 

    } 
    public static void main(String args[]) { 

     if (args.length!=1) { 
      System.out.println("Usage: java -jar <filename.jar> <username>"); 
      return; 
     } else { 
      LunatopiaClient lunatopiaClient = new LunatopiaClient(args[0]); 
      lunatopiaClient.init(); 
     } 

    } 
    public void init() { 

     try { 
      game = new Game(""); 
      container = new AppGameContainer(game); 
      container.setFullscreen(true); 
      game.init(container); 
      game.init(); 
     } catch (SlickException e) { 
      e.printStackTrace(); 
     } 

    } 
    public Game getGame() { 
     return game; 
    } 
    public String getUsername() { 
     return username; 
    } 
} 

類遊戲

import org.newdawn.slick.AppGameContainer; 
import org.newdawn.slick.GameContainer; 
import org.newdawn.slick.SlickException; 
import org.newdawn.slick.state.StateBasedGame; 

public class Game extends StateBasedGame implements Runnable{ 
    public static final int menuState = 0; 
    public static final int gameState = 1; 
    private boolean running; 
    private AppGameContainer container; 
    Thread game; 

    public Game(String name) { 
     super(name); 
    } 
    public void initStatesList(GameContainer container) throws SlickException { 
     this.container = (AppGameContainer) container; 
     addState(new MenuState()); 
     addState(new GameState()); 
    } 
    public void init() throws SlickException { 
     enterState(menuState); 
     game = new Thread(this); 
     game.start(); 
    } 
    public void run() { 
     running = true; 
     while (running) { 
      try { 
       update(container, 0); 
       render(container, container.getGraphics()); 
      } catch (SlickException e) { 
       e.printStackTrace(); 
      } 

     } 
    } 
} 

類MenuState

import org.newdawn.slick.GameContainer; 
import org.newdawn.slick.Graphics; 
import org.newdawn.slick.SlickException; 
import org.newdawn.slick.state.BasicGameState; 
import org.newdawn.slick.state.StateBasedGame; 

public class MenuState extends BasicGameState{ 

    public void init(GameContainer container, StateBasedGame game) 
      throws SlickException { 

    } 
    public void render(GameContainer container, StateBasedGame game, Graphics g) 
      throws SlickException { 
     g.drawString("Hello World", 0, 0); 
    } 
    public void update(GameContainer container, StateBasedGame game, int arg) 
      throws SlickException { 

    } 
    public int getID() { 
     return 0; 
    } 

} 

編輯：拼寫

Answer 1

很遺憾，您在很不正規的莊園配置了很多代碼。首先，Slick2d會自動線程執行你的程序，因此你不需要自己編寫一個線程。

您似乎還在調用不存在的方法，例如init（容器）在遊戲中未定義。此外，您將容器存儲爲不需要的數據值，因此您爲什麼要獲取圖形上下文的NPE。

如果您剛開始使用Slick2d，我建議您查看關於如何入門的新波士頓視頻教程。否則，不幸的是，我相信你可能不得不重新啓動你的項目，因爲它目前的狀態是不可用的。希望這會有所幫助:)