今天在看一個項目的源代碼時,發現了這個電源管理和屏幕鎖:PowerManager、wakelock。
其中在onStart()方法中獲取wakelock,並且在onstop()中將這個lock釋放掉。
protected void onStart() {
....
pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK | PowerManager.ACQUIRE_CAUSES_WAKEUP, "MediaCenterApplication");
wl.acquire();
wl.setReferenceCounted(false);
....
}
protected void onStop() {
....
wl.release();
....
}
- PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);通過
Context.getSystemService()
.方法獲取PowerManager實例。 - 然後通過PowerManager的newWakeLock((int flags, String tag)來生成WakeLock實例。int Flags指示要獲取哪種WakeLock,不同的Lock對cpu 、屏幕、鍵盤燈有不同影響。
- 獲取WakeLock實例後通過acquire()獲取相應的鎖,然後進行其他業務邏輯的操作,最後使用release()釋放(釋放是必須的)。
關於int flags
PARTIAL_WAKE_LOCK:保持CPU 運轉,屏幕和鍵盤燈有可能是關閉的。
SCREEN_DIM_WAKE_LOCK:保持CPU 運轉,允許保持屏幕顯示但有可能是灰的,允許關閉鍵盤燈
SCREEN_BRIGHT_WAKE_LOCK:保持CPU 運轉,允許保持屏幕高亮顯示,允許關閉鍵盤燈
FULL_WAKE_LOCK:保持CPU 運轉,保持屏幕高亮顯示,鍵盤燈也保持亮度
ACQUIRE_CAUSES_WAKEUP:Normal wake locks don't actually turn on the illumination. Instead, they cause the illumination to remain on once it turns on (e.g. from user activity). This flag will force the screen and/or keyboard to turn on immediately, when the WakeLock is acquired. A typical use would be for notifications which are important for the user to see immediately.
ON_AFTER_RELEASE:f this flag is set, the user activity timer will be reset when the WakeLock is released, causing the illumination to remain on a bit longer. This can be used to reduce flicker if you are cycling between wake lock conditions.
權限獲取
另外WakeLock的設置是 Activiy 級別的,不是針對整個Application應用的。