java - Android 执行 if 语句，即使它不应该执行？

Question

好吧，我只是没有其他方式来表达这个，我有一个如下所示的函数:

@Override
public void onSensorChanged(SensorEvent event) {
    old_orientation = orientation;
    if(event.sensor == grav) {
        last_grav_reading = event.values;
    } else {
        last_magnet_reading = event.values;
    }
    if (last_grav_reading != null && last_magnet_reading != null) {
        sensorManager.getRotationMatrix(mat_rotation, mat_inclination, last_grav_reading, last_magnet_reading);
        sensorManager.getOrientation(mat_rotation, orientation);
        if (listener != null) {
            listener.onOrientationSensorUpdate(old_orientation, orientation);
        }
    }
}

所以“getRotationMatrix”应该只在 last_magnet_reading 和 last_grav_reading 都不为零时才执行，对吧？

再次猜测，该行实际上已执行(并导致严重崩溃)，显示案例的图片(所选行是调试器报告正在执行的行，在该行下方您可以看到每个变量的值):

所以....这是怎么回事？ JRE 在 android 上有问题吗？哦，没有其他函数/线程访问这些变量。此外，它不会发生在我的主手机(android 5.0.1)上，但它确实发生在我的辅助手机(4.3)上。(我可以“预期”一个传感器根本不存在，但这仍然会违反该 if 语句)。

编辑，全类:

public class OrientationTracker implements SensorEventListener, IOrientationTracker {
    private SensorManager sensorManager;
    private Sensor magnet;
    private Sensor grav;
    private float[] last_grav_reading;
    private float[] last_magnet_reading;
    private float[] mat_inclination = new float[9];
    private float[] mat_rotation = new float[9];
    private float[] old_orientation;
    private float[] orientation;
    private boolean isRunning;
    private OrientationUpdateListener listener;


    public OrientationTracker(Context context) {
        sensorManager = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE);
        this.magnet = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
        this.grav =  sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY);
        this.orientation = new float[]{0,0,0};
        isRunning = false;
        if (this.magnet != null &&this.grav != null){
            // Success! There's a magnetometer.

        }
    }

    public void start(){
        if(isRunning) {
            //Already running, do nothing
            return;
        }
        registerSensors();
        isRunning = true;
    }
    public void start(OrientationUpdateListener listener) {
        start();
        this.listener = listener;
    }
    public void stop() {
        unregisterSensors();
        isRunning = false;
    }


    public void registerSensors() {
        sensorManager.registerListener(this, magnet, SensorManager.SENSOR_DELAY_NORMAL);
        sensorManager.registerListener(this, grav, SensorManager.SENSOR_DELAY_NORMAL);
    }

    public void unregisterSensors() {
        sensorManager.unregisterListener(this);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        old_orientation = orientation;
        String t = event.sensor.getName();
        String p = grav.getName();
        if(event.sensor.equals(grav)) {
            last_grav_reading = event.values;
        } else {
            last_magnet_reading = event.values;
        }
        if (last_grav_reading != null && last_magnet_reading != null) {
            sensorManager.getRotationMatrix(mat_rotation, mat_inclination, last_grav_reading, last_magnet_reading);
            sensorManager.getOrientation(mat_rotation, orientation);
            if (listener != null) {
                listener.onOrientationSensorUpdate(old_orientation, orientation);
            }
        }
    }
    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
    }
}

并追踪:

"<1> main@830026754464" prio=5 runnable
  java.lang.Thread.State: RUNNABLE
      at com.scoutingstuff.paul.ivossenjacht.OrientationTracker.onSensorChanged(OrientationTracker.java:71)
      at android.hardware.SystemSensorManager$ListenerDelegate$1.handleMessage(SystemSensorManager.java:204)
      at android.os.Handler.dispatchMessage(Handler.java:99)
      at android.os.Looper.loop(Looper.java:137)
      at android.app.ActivityThread.main(ActivityThread.java:5041)
      at java.lang.reflect.Method.invokeNative(Method.java:-1)
      at java.lang.reflect.Method.invoke(Method.java:511)
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
      at dalvik.system.NativeStart.main(NativeStart.java:-1)

"<12> android.hardware.SystemSensorManager$SensorThread@830035660424" prio=5 runnable
  java.lang.Thread.State: RUNNABLE
     Incompatible thread state: thread not suspended

"<11> GLThread 357@830035646696" prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

"<10> Binder_2@830035587352" prio=5 runnable
  java.lang.Thread.State: RUNNABLE
     Incompatible thread state: thread not suspended

"<9> Binder_1@830035581424" prio=5 runnable
  java.lang.Thread.State: RUNNABLE
     Incompatible thread state: thread not suspended

"<8> FinalizerWatchdogDaemon@830035565608" daemon prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

"<7> FinalizerDaemon@830035565176" daemon prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

"<6> ReferenceQueueDaemon@830035564816" daemon prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

"<5> Compiler@830035564576" daemon prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

"<3> Signal Catcher@830035564096" daemon prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

"<2> GC@830035563872" daemon prio=5 waiting
  java.lang.Thread.State: WAITING
     Incompatible thread state: thread not suspended

Answer 1

   (last_grav_reading != null && last_magnet_reading != null)

在您收到重力事件和收到磁铁事件后为真。没有将 last_XXX_reading 返回为 null 的代码。你是说

if(event.sensor == grav) {
    last_magnet_reading = null;
    last_grav_reading = event.values;
} else {
    last_grav_reading = null;
    last_magnet_reading = event.values;
}

两个传感器都连接到同一个监听器 this

    sensorManager.registerListener(this, magnet, SensorManager.SENSOR_DELAY_NORMAL);
    sensorManager.registerListener(this, grav, SensorManager.SENSOR_DELAY_NORMAL);