Android changes the system time zone and SimpleDateFormat cannot output the correct time

platform

RK3288 + Android 7.1

problem

修改系统时区后, 使用SimpleDateFormat 无法转化出正确的时间.

    final String DatePattern = "yyyy-MM-dd HH:mm:ss";
    SimpleDateFormat sdf = new SimpleDateFormat(DatePattern, Locale.getDefault());
    @Override
    protected void onResume() {
    
    
        super.onResume();

        Date date = new Date();
        android.util.Log.d("DateTest", sdf.format(date);
    }

Test steps:

1. Enter test Activity
2. Press HOME to return to Launcher
3. Open Settings -> Time and Date
4. Turn off automatic date and time confirmation, and turn off automatic time zone determination.
5. Choose a time zone different from the current one.
6. Return to test Activity.

During this process, onResume will be executed twice. Assuming that it takes 1 minute in total from 2->6, the time zone is switched from GMT+8 to GMT+1:
The first output time is:
2019-07-17 08:00 :00

The second output time is:
Expected: 2019-07-17 01:01:00
Actual: 2019-07-17 08:01:00

Analysis and solutions

After testing, it was found that the reason is that the time zone in SimpleDateFormat did not change with the actual time zone change:

    final String DatePattern = "yyyy-MM-dd HH:mm:ss";
    SimpleDateFormat sdf = new SimpleDateFormat(DatePattern, Locale.getDefault());

The solution is to recreate SimpleDateFormat after the time zone changes.

    final String DatePattern = "yyyy-MM-dd HH:mm:ss";
    SimpleDateFormat sdf = new SimpleDateFormat(DatePattern, Locale.getDefault());
    @Override
    protected void onResume() {
    
    
        super.onResume();
		sdf = new SimpleDateFormat(DatePattern, Locale.getDefault());
        Date date = new Date();
        android.util.Log.d("DateTest", sdf.format(date);
    }

Expand

In Android, you can trigger the update of the relevant code by registering the time zone change broadcast, reference:
|-- frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/policy/DateView.java

        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_TIME_TICK);
        filter.addAction(Intent.ACTION_TIME_CHANGED);
        filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);
        filter.addAction(Intent.ACTION_LOCALE_CHANGED);
        getContext().registerReceiver(mIntentReceiver, filter, null, null);