java - Android 应用程序在重新启动时崩溃

Question

启动应用程序时，它在以下方法中给出 java 空点错误

 private ParamHandler(Context context) {
      Log.e("ParamHandler : Constructor : Enter"); 
        mContext = context.getApplicationContext();
        mTm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
        mCm = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        mVersionedPsc = VersionedPsc.getInstance(mTm);
        msisdn = getPhoneNumber();
        Log.e("ParamHandler : Constructor : Exit"); 
    }

    public static synchronized ParamHandler getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new ParamHandler(context);
        }
        return mInstance;
}

这是我的 logcat 文件。在第 45 行和第 55 行中给出了空点错误

03-20 07:07:10.662: E/AndroidRuntime(1240): FATAL EXCEPTION: Thread-83
03-20 07:07:10.662: E/AndroidRuntime(1240): Process: com.instantmeter.starter, PID: 1240
03-20 07:07:10.662: E/AndroidRuntime(1240): java.lang.NullPointerException
03-20 07:07:10.662: E/AndroidRuntime(1240):     at com.mobile.instantmeter.service.ParamHandler.<init>(ParamHandler.java:45)
03-20 07:07:10.662: E/AndroidRuntime(1240):     at com.mobile.instantmeter.service.ParamHandler.getInstance(ParamHandler.java:55)
03-20 07:07:10.662: E/AndroidRuntime(1240):     at com.mobile.instantmeter.service.MasterThread.run(MasterThread.java:110)
03-20 07:07:10.662: E/AndroidRuntime(1240):     at java.lang.Thread.run(Thread.java:841)

Answer 1

一定要在ParamHandler(Context context)方法中发送/接收context，可能context为null。那么您不需要使用应用程序上下文设置 mContext 变量。

 private ParamHandler(Context context) {
      Log.e("ParamHandler : Constructor : Enter"); 
       //mContext = context.getApplicationContext();
        mTm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
        mCm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        mVersionedPsc = VersionedPsc.getInstance(mTm);
        msisdn = getPhoneNumber();
        Log.e("ParamHandler : Constructor : Exit"); 
    }

使用包含应用程序上下文的mContext变量的其他选项。

private Context mContext;

  private ParamHandler() {
       Log.e("ParamHandler : Constructor : Enter"); 
        mContext = getApplicationContext();
        mTm = (TelephonyManager) mContext.getSystemService(Context.TELEPHONY_SERVICE);
        mCm = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        mVersionedPsc = VersionedPsc.getInstance(mTm);
        msisdn = getPhoneNumber();
        Log.e("ParamHandler : Constructor : Exit"); 
    }