内容简介:Working with time in Android has always been tricky. People have been using either third party libraries (e.g.Joda-Time,In the latest Android Gradle plugin release (v.4.0.0+), "In general, Kotlin provides its Collections and Stream API replacements which a
Working with time in Android has always been tricky. People have been using either third party libraries (e.g.Joda-Time, ThreeTenBp ) or had to work with the built-in time classes (such asCalendar). The built-in classes, although available in all Android versions, had a not-so-great API, were mutable (so not thread-safe), and timezone handling was a pain ( ref ).
In the latest Android Gradle plugin release (v.4.0.0+), " Java 8+ API desugaring support " was introduced. In plain language, we can use some Java 8 APIs and the plugin will translate those APIs to Android-compatible Java behind the scenes that can be used in all Android versions without requiring a minimum API level!
In general, Kotlin provides its Collections and Stream API replacements which are superior to Java's in my opinion. So from the list of Java 8 APIs , I think that only the excellent java.time API is interesting for a Kotlin developer. Finally, a nice date/time API that can be used in Android!
Note that this "desugaring" process might cost a few extra KB in your APK/AAB. But if that's not a deal-breaker for your case, you should consider using the newer APIs.
Set up
You would need to modify your build.gradle
files. More details (and up-to-date version codes) in the official doc
.
android { [...] defaultConfig { // Required when setting minSdkVersion to 20 or lower multiDexEnabled true } compileOptions { // Flag to enable support for the new language APIs coreLibraryDesugaringEnabled true // Sets Java compatibility to Java 8 sourceCompatibility JavaVersion.VERSION_1_8 targetCompatibility JavaVersion.VERSION_1_8 } [...] } dependencies { [...] coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:1.0.9' [...] }
Meet the classes
The time API is quite comprehensive and the complete exploration of the API is outside of the scope of this post. But, I want to introduce what I believe the main classes you probably going to need most of the time.
Instant
Instant is a point in time. Can be considered equivalent to a timestamp, if you are familiar with that term.
LocalTime, LocalDate, LocalDateTime
Each class represents the time, date, date+time respectively, without a timezone. Most people when thinking about date/time think in these terms anyway.
ZoneOffset, ZoneId
These are used to work with timezones. You would need one of those to convert a Local*
to an Instant
.
ZonedDateTime
You probably guessed it. This is what you get when combine a LocalDateTime
with a ZoneId
. This can be converted to an Instant
.
Playing with date and time
These APIs provide intuitive and consistent ways to manipulate date and time. Remember that all objects are immutable, so a new object is created every time that a manipulation takes place (which is a good thing). Some useful examples follow.
val someDate = LocalDate.of(2020, 7, 28) val someDateTime = LocalDateTime.ofEpochSecond(1595363833) val someInstant = Instant.parse("2007-12-03T10:15:30.00Z")
val today: LocalDate = LocalDate.now() val startOfDay: LocalDateTime = today.atStartOfDay()
LocalDate
val now: LocalDateTime = LocalDateTime.now() val nowInLA: ZonedDateTime = now.atZone(ZoneId.of("America/Los_Angeles"))
val instant: Instant = nowInLA.toInstant() val timestampInSeconds: Long = instant.epochSecond val timestampInMilliseconds: Long = instant.toEpochMilli()
val today: LocalDate = LocalDate.now() val previousWeek: LocalDate = LocalDate.now().minusWeeks(1)
Formatting
Just note that the formatters you are used to in Android, such as SimpleDateFormat
, cannot be used with Java Time API. The API comes with its own formatters, such as DateTimeFormatter
.
DateTimeFormatter.ISO_DATE.format(instant)
Enjoy a modern date/time API in your Android development life :)
很遗憾的说,推酷将在这个月底关闭。人生海海,几度秋凉,感谢那些有你的时光。
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