翻译 SystemClock类

public final class SystemClock 
extends Object 

java.lang.Object   ↳

android.os.SystemClock

Core timekeeping facilities.核心计时方法

Three different clocks are available, and they should not be confused:三个不同的时钟是可用的,他们不应被混淆:

• System.currentTimeMillis() is the standard "wall" clock (time and date) expressing milliseconds since the epoch.//是标准的“wall”钟(日期和时间)时代以来表达毫秒

• The wall clock can be set by the user or the phone network (see setCurrentTimeMillis(long)), so the time may jump backwards or forwards unpredictably.这个时钟可以由用户或手机网络设置(见setCurrentTimeMillis(long)),所以时间可能不可预知的向前或向后跳

•  This clock should only be used when correspondence with real-world dates and times is important, such as in a calendar or alarm clock application.这个时钟只应使用符合真实世界的日期和时间是很重要的,比如在一个日历或闹钟应用程序。

•  Interval or elapsed time measurements should use a different clock. 或时间间隔测量应该使用不同的时钟。

• If you are using System.currentTimeMillis(), consider listening to the ACTION_TIME_TICK,ACTION_TIME_CHANGED and ACTION_TIMEZONE_CHANGED Intent broadcasts to find out when the time changes.

• uptimeMillis() is counted in milliseconds since the system was booted. This clock stops when the system enters deep sleep (CPU off, display dark, device waiting for external input), but is not affected by clock scaling, idle, or other power saving mechanisms. This is the basis for most interval timing such as Thread.sleep(millls), Object.wait(millis), and System.nanoTime(). This clock is guaranteed to be monotonic, and is suitable for interval timing when the interval does not span device sleep. Most methods that accept a timestamp value currently expect the uptimeMillis() clock.

• elapsedRealtime() and elapsedRealtimeNanos() return the time since the system was booted, and include deep sleep. This clock is guaranteed to be monotonic, and continues to tick even when the CPU is in power saving modes, so is the recommend basis for general purpose interval timing.

There are several mechanisms for controlling the timing of events:

• Standard functions like Thread.sleep(millis) and Object.wait(millis) are always available. These functions use the uptimeMillis() clock; if the device enters sleep, the remainder of the time will be postponed until the device wakes up. These synchronous functions may be interrupted withThread.interrupt(), and you must handle InterruptedException.

• SystemClock.sleep(millis) is a utility function very similar to Thread.sleep(millis)//这两个函数非常相似, but it ignores InterruptedException. Use this function for delays if you do not use Thread.interrupt(), as it will preserve the interrupted state of the thread.

• The Handler class can schedule asynchronous callbacks at an absolute or relative time. Handler objects also use the uptimeMillis() clock, and require an event loop (normally present in any GUI application).

• The AlarmManager can trigger one-time or recurring events which occur even when the device is in deep sleep or your application is not running. Events may be scheduled with your choice of currentTimeMillis() (RTC) or elapsedRealtime() (ELAPSED_REALTIME), and cause an Intent broadcast when they occur.

Summary

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Public methods

static long currentThreadTimeMillis()

Returns milliseconds running in the current thread.

static longelapsedRealtime()

Returns milliseconds since boot, including time spent in sleep.

static longelapsedRealtimeNanos()

Returns nanoseconds since boot, including time spent in sleep.

static booleansetCurrentTimeMillis(long millis)

Sets the current wall time, in milliseconds.

static voidsleep(long ms)

Waits a given number of milliseconds (of uptimeMillis) before returning.

static longuptimeMillis()

Returns milliseconds since boot, not counting time spent in deep sleep.

Inherited methods

From class java.lang.Object

Public methods

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currentThreadTimeMillis

Added in API level 1

long currentThreadTimeMillis ()

Returns milliseconds running in the current thread.

Returnslong elapsed milliseconds in the thread

elapsedRealtime

Added in API level 1

long elapsedRealtime ()

Returns milliseconds since boot, including time spent in sleep.

Returnslong elapsed milliseconds since boot.

elapsedRealtimeNanos

Added in API level 17

long elapsedRealtimeNanos ()

Returns nanoseconds since boot, including time spent in sleep.

Returnslong elapsed nanoseconds since boot.

setCurrentTimeMillis

Added in API level 1

boolean setCurrentTimeMillis (long millis)

Sets the current wall time, in milliseconds. Requires the calling process to have appropriate permissions.

Parametersmillis longReturnsboolean if the clock was successfully set to the specified time.

sleep

Added in API level 1

void sleep (long ms)

Waits a given number of milliseconds (of uptimeMillis) before returning. Similar to sleep(long), but does not throw InterruptedException; interrupt()events are deferred until the next interruptible operation. Does not return until at least the specified number of milliseconds has elapsed.

Parametersms long: to sleep before returning, in milliseconds of uptime.

uptimeMillis

Added in API level 1

long uptimeMillis ()

Returns milliseconds since boot, not counting time spent in deep sleep.

Returnslong milliseconds of non-sleep uptime since boot.