Slick2D NullPointerException

Question

我在Slick2D for Java中制作游戲，但是當我試圖顯示一個Image（Slick2D類型）時，它給了我這個錯誤：

java.lang.NullPointerException
at org.newdawn.slick.Graphics.drawImage(Graphics.java:1384)
at org.newdawn.slick.Graphics.drawImage(Graphics.java:1433)
at luke_r.games.java.broadway.states.M.render(M.java:21)
at org.newdawn.slick.state.StateBasedGame.render(StateBasedGame.java:199)
at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:688)
at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:411)
at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:321)
at luke_r.games.java.broadway.C.main(C.java:21)

這是M類（不包括導入和類聲明，它們是不需要的）：

@Override
public void init(GameContainer gc, StateBasedGame sbg) throws SlickException
{
    PL.x = 100;
    PL.y = 100;
}
@Override
public void render(GameContainer gc, StateBasedGame sbg, Graphics g) throws SlickException
{
    g.drawImage(I.title, 0, 0); //Line 21, the error
    PL.render(g);
}
@Override
public void update(GameContainer gc, StateBasedGame sbg, int delta) throws SlickException
{}
@Override
public int getID()
{
    return 0;
}

Answer 1

問題是I.title == null。 將其設置為正確的值。

Answer 2

在init函數中將圖像的url設置為I.title，我的意思是=> I.title = new Image（“ - your URL-”）; Slick2D以這種形式工作：首先，他在方法init中初始化所有參數，然后直到發生更改當前狀態“he”render => update => render => update => render => update ... You可以使用SetTargetFrameRate方法設置更新將在SetUpClass中發生多少。