Saturday 25 November 2017
How to normalize dates for Android App
Answer
Answer
I want to store dates in my Cloud
database all under one time-zone and then for all my users (whose Android devices could
be anywhere in the world), I want that date to be converted and displayed for them with
whatever their default Android settings
are.
it shows how to store dates as a long with Java in code using
this:System.currentTimeMillis()
1)
However, how do I "normalize" the date to be UTC (this is what I hear everyone saying I
should do)?
2) Then, after that date is
retrieved from the Cloud DB, how do I with Java convert that UTC date to whatever the
time-zone of the device the app is installed on
is?
From what I gather, Android might
do some of this stuff automatically, but I am not sure what - and I am not sure what I
myself have to do. Could someone clarify the above for
me?
Thanks.
Answer
According to the docs
System.currentTimeMillis() returns a UTC timestamp. In other
words, assuming the device has synchronized to a time server before you get the
timestamp (which is very likely), it will not include a time zone
adjustment.
rel="noreferrer">http://developer.android.com/reference/java/lang/System.html#currentTimeMillis()
Similarly,
if you retrieve the timestamp and use a Calendar object, the
Calendar should adjust to the Locale
of the device if you use Calendar.setTimeInMillis(long
milliseconds)
rel="noreferrer">http://developer.android.com/reference/java/util/Calendar.html#Calendar()
rel="noreferrer">http://developer.android.com/reference/java/util/Calendar.html#setTimeInMillis(long)
In
other words, you really don't have to "normalize" this information, Linux/Java does it
for you. What you have to worry about is getting timestamps from email, messages or
other systems that have already have a Locale adjustment,
correct or not. These are the difficult timestamp problems.
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