JME3 引擎和 nullPointerException

Question

所以这个问题适合那些熟悉 jMonkey 3 引擎的人。我的simpleUpdate() 循环中有这段代码：

@Override
    public void simpleUpdate(float lastTimePerFrame) {
        if (load) {
            if (frameCount == 1) {
                Element element = nifty.getScreen("loadlevel").findElementByName("loadingtext");
                textRenderer = element.getRenderer(TextRenderer.class);
                inputManager.setCursorVisible(true);
                flyCam.setDragToRotate(true);
                CubesTestAssets.registerBlocks();

                setProgress(0.2f, "Registering Blocks");
            } else if (frameCount == 2) {
                initBlockTerrain();

                setProgress(0.4f, "Generating Chunk");
            } else if (frameCount == 3) {
                initControls();
                initPlayer();

                setProgress(0.6f, "Setting Up Player");
            } else if (frameCount == 4) {
                viewPort.setBackgroundColor(ColorRGBA.Cyan);

                setProgress(0.8f, "Creating Sky");
            } else if (frameCount == 5) {
                inputManager.setCursorVisible(false);
                flyCam.setDragToRotate(false);

                setProgress(1.0f, "Done");
            } else if (frameCount == 6) {
                nifty.gotoScreen("end");
                nifty.exit();
                guiViewPort.removeProcessor(niftyDisplay);
            }
            frameCount++;
        }
        cubesSettings = CubesTestAssets.getSettings(this);
        playerControl = new CharacterControl();
        float playerMoveSpeed = ((cubesSettings.getBlockSize() * 2.5f) * lastTimePerFrame);
        Vector3f camDir = cam.getDirection().mult(playerMoveSpeed);
        Vector3f camLeft = cam.getLeft().mult(playerMoveSpeed);
        walkDirection.set(0, 0, 0);
        if(arrowKeys[0]){ walkDirection.addLocal(camDir); }
        if(arrowKeys[1]){ walkDirection.addLocal(camLeft.negate()); }
        if(arrowKeys[2]){ walkDirection.addLocal(camDir.negate()); }
        if(arrowKeys[3]){ walkDirection.addLocal(camLeft); }
        walkDirection.set(0, 0, 0);
        walkDirection.setY(0);
        playerControl.setWalkDirection(walkDirection);
        cam.setLocation(playerControl.getPhysicsLocation());
    }

我只剩下这个 nullPointerException：

SEVERE: Uncaught exception thrown in Thread[LWJGL Renderer Thread,5,main]
java.lang.NullPointerException
    at com.jme3.bullet.objects.PhysicsCharacter.setWalkDirection(PhysicsCharacter.java:115)
    at com.bminus.Main.simpleUpdate(Main.java:219)
    at com.jme3.app.SimpleApplication.update(SimpleApplication.java:242)
    at com.jme3.system.lwjgl.LwjglAbstractDisplay.runLoop(LwjglAbstractDisplay.java:151)
    at com.jme3.system.lwjgl.LwjglDisplay.runLoop(LwjglDisplay.java:185)
    at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:228)
    at java.lang.Thread.run(Thread.java:744)

第 219 行是这一行：

playerControl.setWalkDirection(walkDirection);

我已经检查过了，playerControl 和 walkDirection 都不是空的。我的问题是：还有什么可能是空的？我该如何解决这个错误？为什么会这样？我如何防止这种情况在未来发生？对此问题的任何帮助将不胜感激，如果您需要查看完整代码，请询问！我非常乐意与您分享！提前致谢！

Answer 1

如果您在不带参数的情况下实例化 CharacterControl，则不会初始化 PhysicsCharacter 类中的 character 成员。

完整的跟踪将是：

=>  simpleUpdate()
    =>  playerControl.setWalkDirection()
        =>  character.setWalkDirection(Converter.convert(walkDirection, tempVec));
            => NullPointerException on character object

这是问题所在，当您调用方法 playerControl.setWalkDirection 时。

所以你必须使用另一个构造函数，比如CharacterControl(CollisionShape shape, float stepHeight)。

CapsuleCollisionShape capsuleShape = new CapsuleCollisionShape(1.5f, 6f, 1);
playerControl = new CharacterControl(capsuleShape, 0.5f);

有关参数值和其他内容，请参阅：

• CapsuleCollisionShape
• CharacterControl
• PhysicsCharacter