Android Activity - NullPointerException（“无法实例化活动ComponentInfo”）？

我正在尝试为Android创建一个程序。但是，每当我在AVD上运行它时，它会在LogCat中返回一个错误，说我的代码中有一个NullPointerException，因此它“无法实例化活动ComponentInfo”。Android Activity - NullPointerException（“无法实例化活动ComponentInfo”）？

这里是我的代码：

package com.example.sensor; 

import android.app.Activity; 
import android.os.Bundle; 
import android.hardware.SensorManager; 
import android.hardware.Sensor; 
import android.hardware.SensorEventListener; 
import android.hardware.SensorEvent; 
import android.os.Bundle; 
import android.app.Activity; 
import android.view.Menu; 
import android.widget.TextView; 

public class MainActivity extends Activity { 

    private SensorManager sensorMgr; 
    private TextView result; 
    Sensor sensor = sensorMgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); 
    private float x, y, z; 
    protected void onCreate(Bundle savedInstanceState) { 

     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

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

     sensorMgr = (SensorManager)getSystemService(SENSOR_SERVICE); 
     SensorEventListener lsn = new SensorEventListener() { 
      @SuppressWarnings("deprecation") 
      public void onSensorChanged(SensorEvent e) { 
      float[] values = e.values; 
      x = e.values[SensorManager.DATA_X]; 
      y = e.values[SensorManager.DATA_Y]; 
      z = e.values[SensorManager.DATA_Z]; 
      result.setText("x="+(int)x+","+"y="+(int)y+","+"z="+(int)z); 
      } 
      public void onAccuracyChanged(Sensor s, int accuracy) { 
      } 
     }; 
     sensorMgr.registerListener(lsn, sensor, SensorManager.SENSOR_DELAY_GAME); 
    } 

    @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; 
    } 
}

这里是我的xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    tools:context=".MainActivity" > 

    <TextView 
     android:id="@+id/result" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerHorizontal="true" 
     android:layout_centerVertical="true" /> 

</RelativeLayout>

这里是logcat的：

05-28 13:07:49.896: D/AndroidRuntime(8658): Shutting down VM 
05-28 13:07:49.896: W/dalvikvm(8658): threadid=1: thread exiting with uncaught exception (group=0x400205a0) 
05-28 13:07:49.906: E/AndroidRuntime(8658): FATAL EXCEPTION: main 
05-28 13:07:49.906: E/AndroidRuntime(8658): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.sensor/com.example.sensor.MainActivity}: java.lang.NullPointerException 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1743) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1851) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.ActivityThread.access$1500(ActivityThread.java:132) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1038) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.os.Looper.loop(Looper.java:150) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.ActivityThread.main(ActivityThread.java:4277) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at java.lang.reflect.Method.invoke(Method.java:507) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at dalvik.system.NativeStart.main(Native Method) 
05-28 13:07:49.906: E/AndroidRuntime(8658): Caused by: java.lang.NullPointerException 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at com.example.sensor.MainActivity.<init>(MainActivity.java:39) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at java.lang.Class.newInstanceImpl(Native Method) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at java.lang.Class.newInstance(Class.java:1409) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.Instrumentation.newActivity(Instrumentation.java:1040) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1735) 
05-28 13:07:49.906: E/AndroidRuntime(8658):  ... 11 more 
05-28 13:07:52.018: I/Process(8658): Sending signal. PID: 8658 SIG: 9 
05-28 13:28:55.300: D/AndroidRuntime(8707): Shutting down VM 
05-28 13:28:55.300: W/dalvikvm(8707): threadid=1: thread exiting with uncaught exception (group=0x400205a0) 
05-28 13:28:55.310: E/AndroidRuntime(8707): FATAL EXCEPTION: main 
05-28 13:28:55.310: E/AndroidRuntime(8707): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.sensor/com.example.sensor.MainActivity}: java.lang.NullPointerException 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1743) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1851) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.ActivityThread.access$1500(ActivityThread.java:132) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1038) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.os.Looper.loop(Looper.java:150) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.ActivityThread.main(ActivityThread.java:4277) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at java.lang.reflect.Method.invoke(Method.java:507) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at dalvik.system.NativeStart.main(Native Method) 
05-28 13:28:55.310: E/AndroidRuntime(8707): Caused by: java.lang.NullPointerException 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at com.example.sensor.MainActivity.<init>(MainActivity.java:39) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at java.lang.Class.newInstanceImpl(Native Method) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at java.lang.Class.newInstance(Class.java:1409) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.Instrumentation.newActivity(Instrumentation.java:1040) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1735) 
05-28 13:28:55.310: E/AndroidRuntime(8707):  ... 11 more 
05-28 13:28:57.262: I/Process(8707): Sending signal. PID: 8707 SIG: 9

有谁知道什么可能会造成这个？非常感谢。

来源

2013-05-28 Entel

请张贴logcat的输出，你叫'super.onCreate（savedInstanceState）;'你的代码中两次，检查太:) – reidzeibel

请显示日志猫 – asloob

移动Sensor sensor = sensorMgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);里面onCreate后sensorMgr = (SensorManager)getSystemService(SENSOR_SERVICE);

来源

2013-05-28 05:31:24

非常感谢，它的工作原理。 – Entel

你叫

super.onCreate(savedInstanceState);

方法两次。

来源

2013-05-28 05:27:02 stinepike

中给出的错误，但它不应该导致nullpointerexception ...更好地发布logcat错误日志 – stinepike

非常感谢！ – Entel

你缺少这一行。

 sensorMgr = (SensorManager)getSystemService(SENSOR_SERVICE); 
     //sensorMgr not initialized. probably gettinh NullPointerException

还可以使用上述中的onCreate（PARAM）

 protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); // call this once 
     setContentView(R.layout.activity_main); 
     sensorMgr = (SensorManager)getSystemService(SENSOR_SERVICE); // initialize 
     Sensor sensor = sensorMgr.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); 
     result = (TextView)findViewById(R.id.textView1); 
     ..... 
     }

来源

2013-05-28 05:31:31 Raghunandan

非常感谢！ – Entel

Android Activity - NullPointerException（“无法实例化活动ComponentInfo”）？

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