getSimSerialNumber何时返回空值？

Question

所以这就是场景。

当我第一次测试我使用的应用程序时 getSimSerialNumber（）函数，我成功将我的SIM号码设为“89912000107679766XYZ”。

现在，每当我运行相同的功能时，无论飞行模式是打开还是关闭，我都会获得Null值。

我尝试使用getSimState（）进行检查，并且总是得到Constant值5，即“SIM_STATE_READY”。

问题究竟在哪里？为什么我现在不能获得正确的SimSerialNumber？

编辑1：

参考代码库：

public void doSimStateCheck(Context c){
        String savedSimCardNo = ClientConfig.readSimCardNumber(c); // I have saved device's sim card somewhere here.
        String existingSimCardNo = ""; 
        TelephonyManager tm = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
        String simID = "";
        boolean airPlaneMode = isAirplaneModeOn(c);
        if(airPlaneMode){
            // toggle airplane mode
            setAirplaneModeOn(c,0); //Setting Airplane mode on - this might not work as stated for Jellybean and above. I have given WRITE_SETTINGS and WRITE_SECURE_SETTINGS permission already. I am not worried about this piece of code anyways.
            simID = tm.getSimSerialNumber();
            setAirplaneModeOn(c, 1); //Setting Airplane mode back to off.
        }
        else{
            simID = tm.getSimSerialNumber(); // I am getting null here, i.e. when Airplane mode is NOT on, still I get null :( THIS IS MY CONCERN.
        }

        if (simID != null)
            existingSimCardNo = simID;
        else{
            Log.v("SimState",""+tm.getSimState()); // This always returns 5.
            existingSimCardNo = "NULL";
        }

        Log.v("SavedSimCardState", "It is " + savedSimCardNo); //This returns 89912000107679766XYZ
        Log.v("ExistingSimCardState","It is "+existingSimCardNo); //This shows NULL as stated above.
        if(!savedSimCardNo.equals(existingSimCardNo)){
           //do stuff when sim card numbers are not same as saved earlier.
        }
    }

    @SuppressWarnings("deprecation")
    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
    public static boolean isAirplaneModeOn(Context context) {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
            return Settings.System.getInt(context.getContentResolver(),
                    Settings.System.AIRPLANE_MODE_ON, 0) != 0;
        } else {
            return Settings.Global.getInt(context.getContentResolver(),
                    Settings.Global.AIRPLANE_MODE_ON, 0) != 0;
        }
    }

    @SuppressWarnings("deprecation")
    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
    public static void setAirplaneModeOn(Context context,int state) {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
            Settings.System.putInt(context.getContentResolver(),
                    Settings.System.AIRPLANE_MODE_ON, state);
        } else {
            Settings.Global.putInt(context.getContentResolver(),
                    Settings.Global.AIRPLANE_MODE_ON, state);
        }
    }