我已经制作了简单的 JFrame，它工作正常，除非当我尝试从其他类访问它时它返回 null。所以我为它做了 getter (public static JFrame getWindow()) 它返回 null。如果我将 JFrame 设置为 public 并尝试以这种方式访问它，它将返回 null。当我创建时，它在游戏引擎启动后立即变为空。
主要:
public class Main {
private static String title = "2D SquareWorld 0.";
private static String version = "";
private static JFrame window;
private static Container container;
public static void main(String[] args) {
GameEngine game = new GameEngine();
window = new JFrame();
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setTitle(title + Version.newVersion());
window.setResizable(false);
window.add(game);
window.setSize(1000, 720);
window.setLocationRelativeTo(null);
window.setVisible(true);
game.start();
}
public static Container getContainer() {
return container;
}
public static JFrame getWindow() {
return window;
}
}
游戏引擎:
package GameEngine;
public class GameEngine extends Canvas implements Runnable, KeyListener, MouseListener, MouseMotionListener {
private static final long serialVersionUID = 1L;
private Thread thread;
private boolean running;
private GameStateManager gsm;
public GameEngine() {
gsm = new GameStateManager();
}
public void start() {
thread = new Thread(this, "Game");
thread.start();
running = true;
init();
}
public void init() {
Data.setValue("ScreenWidth", getWidth());
Data.setValue("ScreenHeight", getHeight());
addKeyListener(this);
}
public void update(double delta) {
}
public void render() {
BufferStrategy bs = getBufferStrategy();
if(bs == null) {
createBufferStrategy(2);
return;
}
Graphics g = bs.getDrawGraphics();
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.white);
g2.fillRect(0, 0, getWidth(), getHeight());
gsm.draw(g2);
g2.dispose();
bs.show();
}
public void run() {
long lastLoopTime = System.nanoTime();
long lastFpsTime = 0;
final int TARGET_FPS = Fps.TargetFPS;
final long OPTIMAL_TIME = 1000000000 / TARGET_FPS;
int CurrentFps = 0;
while(running) {
long now = System.nanoTime();
long updateLength = now - lastLoopTime;
lastLoopTime = now;
double delta = updateLength / ((double) OPTIMAL_TIME);
lastFpsTime += updateLength;
CurrentFps++;
if (lastFpsTime >= 1000000000) {
Fps.FPS = CurrentFps;
lastFpsTime = 0;
CurrentFps = 0;
}
update(delta);
render();
try {
if(((lastLoopTime-System.nanoTime() + OPTIMAL_TIME) / 1000000) >= 1) {
Thread.sleep((lastLoopTime-System.nanoTime() + OPTIMAL_TIME) / 1000000);
}
}catch(InterruptedException IE) {
}
}
}
public void mouseDragged(MouseEvent me) {
}
public void mouseMoved(MouseEvent me) {
}
public void mouseClicked(MouseEvent me) {
}
public void mouseEntered(MouseEvent me) {
}
public void mouseExited(MouseEvent me) {
}
public void mousePressed(MouseEvent me) {
}
public void mouseReleased(MouseEvent me) {
}
public void keyPressed(KeyEvent ke) {
gsm.keyPressed(ke.getKeyCode());
}
public void keyReleased(KeyEvent ke) {
}
public void keyTyped(KeyEvent ke) {
}
}
我从这个类中调用了 getWindow:
public class LoginState extends GameState {
private GameStateManager gsm;
public LoginState(GameStateManager gsm) {
this.gsm = gsm;
}
private JTextField username;
private JTextField password;
public void init() {
username = new JTextField(25);
username.setVisible(true);
username.setBounds(20, 20, 50, 50);
Main.getWindow().add(username);
}
public void draw(Graphics2D g) {
g.setColor(Color.gray);
//g.fillRect(0, 0, Data.getIntegerValue("ScreenWidth"), Data.getIntegerValue("ScreenHeight"));
}
游戏状态管理器:
public class GameStateManager {
private ArrayList<GameState> gameStates;
public static final int LOGINSTATE = 0;
public static final int MENUSTATE = 1;
public static final int PLAYSTATE = 2;
private static int currentState;
public GameStateManager() {
gameStates = new ArrayList<GameState>();
currentState = LOGINSTATE;
gameStates.add(new LoginState(this));
gameStates.add(new MenuState(this));
gameStates.add(new PlayState(this));
gameStates.get(currentState).init();
}
请帮忙。
最佳答案
感谢您的更新，但是...您仍然没有显示 LoginWindow 的初始化位置。
猜测 - 您的程序是从与您显示的不同的 main 方法开始的，因此创建 JFrame 并将其分配给静态窗口字段的 main 方法永远不会被调用。我建议您避免以这种方式使用静态方法和字段，它们依赖于 main 方法来初始化。 Java 是一种 OOP 语言 - 因此，请使您的代码符合 OOP 要求，并在保证被调用的代码中创建所需的对象，然后将它们分配给非静态字段。
编辑: 只需交换两行即可:
GameEngine game = new GameEngine();
window = new JFrame();
至
window = new JFrame();
GameEngine game = new GameEngine();
关于Java简单JFrame为null，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34908988/