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SystemClock简介  

2012-02-08 16:52:16|  分类: Android基础 |  标签: |举报 |字号 订阅

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原文:http://developer.android.com/reference/android/os/SystemClock.html#elapsedRealtime()
android.os.SystemClock

Class Overview

Core timekeeping facilities.

Three different clocks are available, and they should not be confused:

  • System.currentTimeMillis() is the standard "wall" clock (time and date) expressing milliseconds since the epoch. 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. 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. Interval or elapsed time measurements should use a different clock. If you are using System.currentTimeMillis(), consider listening to the ACTION_TIME_TICKACTION_TIME_CHANGED andACTION_TIMEZONE_CHANGED Intent broadcasts to find out when the time changes.

    该时间是基于世界时间的,它返回的是从January 1, 1970 00:00:00 UTC到现在时间已经逝去了多多少millisecond,当我设置Android手机的系统时间时,会应该影响该值。

  • 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 asThread.sleep(millls)Object.wait(millis), and System.nanoTime(). This clock is guaranteed to be monotonic, and is the recommended basis for the general purpose interval timing of user interface events, performance measurements, and anything else that does not need to measure elapsed time during device sleep. Most methods that accept a timestamp value expect the uptimeMillis() clock.

    它表示的是手机从启动到现在的运行时间,且不包括系统sleep(CPU关闭)的时间,很多系统的内部时间都是基于此,比如Thread.sleep(millls)Object.wait(millis), and System.nanoTime()

  • elapsedRealtime() is counted in milliseconds since the system was booted, including deep sleep. This clock should be used when measuring time intervals that may span periods of system sleep.

    它表示的是手机从启动到现在的运行时间,且包括系统sleep(CPU关闭)的时间

There are several mechanisms for controlling the timing of events:

Summary

Public Methods
static longcurrentThreadTimeMillis()
Returns milliseconds running in the current thread.
static longelapsedRealtime()
Returns milliseconds 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.
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