12/24-hour mode conflict

android, android-timepicker, simpledateformat

Solution

If you have specified a pattern in `SimpleDateFormat` then you have fixed the 12/24-hour mode, either 12-hour-mode in case of pattern symbol "h" (1-12) or 24-hour-mode in case of pattern symbol "H" (0-23). The alternatives "k" and "K" are similar with slightly different ranges.

That said, specifying a pattern makes your format independent from device setting!

The alternative would be to use DateFormat.getDateTimeInstance() which makes the time style dependent on system locale (if `Locale.getDefault()` might change - or you have to deploy a mechanism how to ask the current device locale and then to set in Android-Java `Locale.setDefault()`).

Another idea specific for Android is to ask directly the system settings using the string constant TIME_12_24 and then to specify a pattern dependent on this setting. This also seems to be possible by special method DateFormat.is24HourFormat() (note for your attention that Android has TWO different classes with name `DateFormat`). Concrete example for this approach:

boolean twentyFourHourStyle = 
  android.text.format.DateFormat.is24HourFormat((Context) this);
DateFormat df = DateFormat.getTimeInstance(DateFormat.SHORT, Locale.getDefault());
if (df instanceof SimpleDateFormat) {
  String pattern = ((SimpleDateFormat) df).toPattern();
  if (twentyFourHourStyle) {
    df = new SimpleDateFormat(pattern.replace("h", "H"), Locale.getDefault());
  } else {
    df = new SimpleDateFormat(pattern.replace("H", "h"), Locale.getDefault());
  }
} else {
  // nothing to do or change
}

You are of course free to refine the code for possible occurrences of k and K or watch out for use of literals h and H (then parse for apostrophs to ignore such parts in replace-method).

Problem

I am a French Android developer, so using `Locale.getDefault()` causes my `DateFormat` to use a 24-hour mode. But, when I set manually my device to 12-hour mode via the setting menu, `DateFormat` keeps going in a 24-hour format. On the contrary, `TimePicker`s are set according to my own 12/24-hour setting. Is there any way to make `DateFormat`s behave the same way as `TimePicker`s ? EDIT: Here is my `DateFormat` declaration: ``` timeFormat = DateFormat.getTimeInstance(DateFormat.SHORT, Locale.getDefault()); ``` And here is where I set my `TimePicker`to 12 or 24-hour mode. ``` tp.setIs24HourView(android.text.format.DateFormat.is24HourFormat((Context) this)); ``` My Solution: According to @Meno Hochschild's answer below, here is how I solved this tricky problem: ``` boolean is24hour = android.text.format.DateFormat.is24HourFormat((Context) this); tp.setIs24HourView(is24hour); // tp is the TimePicker timeFormat = DateFormat.getTimeInstance(DateFormat.SHORT, Locale.getDefault()); if (timeFormat instanceof SimpleDateFormat) { String pattern = ((SimpleDateFormat) timeFormat).toPattern(); if (is24hour) { timeFormat = new SimpleDateFormat(pattern.replace("h", "H").replace(" a",""), Locale.getDefault()); } else { timeFormat = new SimpleDateFormat(pattern.replace("H", "h"), Locale.getDefault()); } } ``` After this, `timeFormat` will correctly format dates whether your device is set to display times in a 24-hour format or in a 12-hour one. And the `TimePicker` will be correctly set too.

Original source