在课堂上编码 android Accelerometer

Question

我正在编写一个显示加速度计读数的应用程序，昨天我能够在主要活动中编写所有加速度计代码，它在模拟器和我的设备上运行良好。

但是今天我试图创建一个包含所有加速度计代码的函数并返回整数数组中的三个整数 X、Y、Z，所以我编写了一个我认为正确的代码，但每次我运行项目模拟器给出错误“不幸的是应用程序名称已停止”。

所以我希望任何帮助，请。

LogCat：

04-27 20:39:27.098: W/dalvikvm(812): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
04-27 20:39:27.118: E/AndroidRuntime(812): FATAL EXCEPTION: main
04-27 20:39:27.118: E/AndroidRuntime(812): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.accelerometer_sensor/com.example.accelerometer_sensor.MainActivity}: java.lang.NullPointerException
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.os.Looper.loop(Looper.java:137)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.ActivityThread.main(ActivityThread.java:5039)
04-27 20:39:27.118: E/AndroidRuntime(812):  at java.lang.reflect.Method.invokeNative(Native Method)
04-27 20:39:27.118: E/AndroidRuntime(812):  at java.lang.reflect.Method.invoke(Method.java:511)
04-27 20:39:27.118: E/AndroidRuntime(812):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-27 20:39:27.118: E/AndroidRuntime(812):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-27 20:39:27.118: E/AndroidRuntime(812):  at dalvik.system.NativeStart.main(Native Method)
04-27 20:39:27.118: E/AndroidRuntime(812): Caused by: java.lang.NullPointerException
04-27 20:39:27.118: E/AndroidRuntime(812):  at com.example.accelerometer_sensor.AccelerometerClass.AccelerometerInit(AccelerometerClass.java:20)
04-27 20:39:27.118: E/AndroidRuntime(812):  at com.example.accelerometer_sensor.MainActivity.onCreate(MainActivity.java:19)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.Activity.performCreate(Activity.java:5104)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
04-27 20:39:27.118: E/AndroidRuntime(812):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
04-27 20:39:27.118: E/AndroidRuntime(812):  ... 11 more
04-27 20:39:30.119: I/Process(812): Sending signal. PID: 812 SIG: 9

这是我的主要活动代码：

 package com.example.accelerometer_sensor;
    import android.os.Bundle;
    import android.app.Activity;
    import android.view.Menu;
    import android.widget.TextView;

    public class MainActivity extends Activity {

        int [] AccVal = new int[3];
        AccelerometerClass acc = new AccelerometerClass();
        TextView acceleration;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
             acc = new AccelerometerClass();

              AccVal = acc.AccelerometerInit();

                acceleration = (TextView)findViewById(R.id.acceleration);

                acceleration.setText("X: "+AccVal[0]+
                        "Y: "+AccVal[1]+
                        "Z: "+AccVal[2]);
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.activity_main, menu);
            return true;
        }


    }

这是我的 AccelerometerClass 代码 ::

package com.example.accelerometer_sensor;

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;

public class AccelerometerClass implements SensorEventListener 
{
    private static Context context;

    int [] Vals = new int[3];

    public int [] AccelerometerInit()
    {
        Sensor accelerometer;
        SensorManager sm;

        sm = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE);       
        accelerometer=sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        sm.registerListener(this, accelerometer,SensorManager.SENSOR_DELAY_NORMAL); 

        return Vals;
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // TODO Auto-generated method stub
        Vals[0]=(int)event.values[0];
        Vals[1]=(int)event.values[1];
        Vals[2]=(int)event.values[2];

    }

}

谢谢。

Answer 1

您在AccelerometerClass 中的上下文永远不会设置！

可能的解决方案：

public class AccelerometerClass implements SensorEventListener {

    int[] Vals = new int[3];

    public int[] AccelerometerInit(Context context) {
        SensorManager sm = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
        Sensor accelerometer = sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        sm.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_NORMAL);

        return Vals;
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {

    }

     @Override
     public void onSensorChanged(SensorEvent event) {
         Vals[0] = (int) event.values[0];
         Vals[1] = (int) event.values[1];
         Vals[2] = (int) event.values[2];
    }
}

在您的活动中使用

AccelerometerClass ac = new AccelerometerClass();
ac.AccelerometerInit(this);