Android显示电池电量时出错

大家好，我正试图在文本视图中显示电池电量，但它给了我错误。 我的Logcat错误和代码如下所示

Logcat 主要活动

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我做错了什么？？提前感谢。

可能是您应该检查对象contentTxt是否为空。在初始化contentTxt之前，您可能会遇到同步问题，从而导致呼叫接收器。 否则，检查意图不为空

01-03 21:28:14.992: E/AndroidRuntime(9599): FATAL EXCEPTION: main
01-03 21:28:14.992: E/AndroidRuntime(9599): Process: com.Designproshop.solarchargerprank, PID: 9599
01-03 21:28:14.992: E/AndroidRuntime(9599): java.lang.RuntimeException: Error receiving broadcast Intent { act=android.intent.action.BATTERY_CHANGED flg=0x60000010 (has extras) } in com.Designproshop.solarchargerprank.MainActivity$1@41b021c0
01-03 21:28:14.992: E/AndroidRuntime(9599):     at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:782)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at android.os.Handler.handleCallback(Handler.java:733)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at android.os.Handler.dispatchMessage(Handler.java:95)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at android.os.Looper.loop(Looper.java:146)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at android.app.ActivityThread.main(ActivityThread.java:5511)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at java.lang.reflect.Method.invokeNative(Native Method)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at java.lang.reflect.Method.invoke(Method.java:515)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at dalvik.system.NativeStart.main(Native Method)
01-03 21:28:14.992: E/AndroidRuntime(9599): Caused by: java.lang.NullPointerException
01-03 21:28:14.992: E/AndroidRuntime(9599):     at com.Designproshop.solarchargerprank.MainActivity$1.onReceive(MainActivity.java:28)
01-03 21:28:14.992: E/AndroidRuntime(9599):     at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:772)
01-03 21:28:14.992: E/AndroidRuntime(9599):     ... 9 more

 public class MainActivity extends ActionBarActivity {
   private TextView contentTxt;
   private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver(){
    @Override
    public void onReceive(Context arg0, Intent intent) {
      // TODO Auto-generated method stub
      int level = intent.getIntExtra("level", 0);
      contentTxt.setText(Integer.toString(level)+ "%");
    }
  };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
     getActionBar().hide();
      setContentView(R.layout.fragment_main);
       new CountDownTimer(5000,1000){
        @Override
        public void onTick(long millisUntilFinished){} 
        @Override
        public void onFinish(){
          //set the new Content of your activity
          MainActivity.this.setContentView(R.layout.chargingactivity);
        }
        }.start();
        contentTxt = (TextView) this.findViewById(R.id.btrylevel);
        this.registerReceiver(this.mBatInfoReceiver, 
        new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

}}