android 4.2以上版本永不休眠 .

android4.2以上版本比android4.2以前的版本framework层框架部分有了很大的改变，androd4.2以前版本framework层给上的接口函数与android4.2以上版本的接口函数也有了些变化，以前让机器永不休眠的方法用在android4.2以上版本已经不起作用了。现将android4.2以上版本修改永不休眠的方法记录下来。

首先还是要修改defaults.xml文件里def_screen_off_timeout的值。

1.  修改default值，不自动休眠

      /frameworks/base/packages/SettingsProvider/res/values/defaults.xml

      修改def_screen_off_timeout为-1

2.修改PowerManagerService.java文件getScreenOffTimeoutLocked()函数

    /frameworks\base\services\java\com\android\server\power\PowerManagerService.java

  修改前：

1. private int getScreenOffTimeoutLocked() {  
2.         int timeout = mScreenOffTimeoutSetting;  
3.         if (isMaximumScreenOffTimeoutFromDeviceAdminEnforcedLocked()) {  
4.             timeout = Math.min(timeout, mMaximumScreenOffTimeoutFromDeviceAdmin);  
5.         }  
6.         if (mUserActivityTimeoutOverrideFromWindowManager >= 0) {  
7.             timeout = (int)Math.min(timeout, mUserActivityTimeoutOverrideFromWindowManager);  
8.         }  
9.          
10.         return Math.max(timeout, MINIMUM_SCREEN_OFF_TIMEOUT);  
11.     }  

private int getScreenOffTimeoutLocked() {        int timeout = mScreenOffTimeoutSetting;        if (isMaximumScreenOffTimeoutFromDeviceAdminEnforcedLocked()) {            timeout = Math.min(timeout, mMaximumScreenOffTimeoutFromDeviceAdmin);        }        if (mUserActivityTimeoutOverrideFromWindowManager >= 0) {            timeout = (int)Math.min(timeout, mUserActivityTimeoutOverrideFromWindowManager);        }               return Math.max(timeout, MINIMUM_SCREEN_OFF_TIMEOUT);    }

修改后:

1. int nosleep;  
2. int timeout = mScreenOffTimeoutSetting;  
3. if (isMaximumScreenOffTimeoutFromDeviceAdminEnforcedLocked()) {  
4.     timeout = Math.min(timeout, mMaximumScreenOffTimeoutFromDeviceAdmin);  
5. }  
6. if (mUserActivityTimeoutOverrideFromWindowManager >= 0) {  
7.     timeout = (int)Math.min(timeout, mUserActivityTimeoutOverrideFromWindowManager);  
8. }  
9. nosleep = mScreenOffTimeoutSetting;  
10. if(nosleep  < 0)  
11. {  
12.     nosleep = mMaximumScreenOffTimeoutFromDeviceAdmin ;  
13.     return Math.max(nosleep, mMaximumScreenOffTimeoutFromDeviceAdmin);  
14. }  
15. return Math.max(timeout, MINIMUM_SCREEN_OFF_TIMEOUT);  

        int nosleep;        int timeout = mScreenOffTimeoutSetting;        if (isMaximumScreenOffTimeoutFromDeviceAdminEnforcedLocked()) {            timeout = Math.min(timeout, mMaximumScreenOffTimeoutFromDeviceAdmin);        }        if (mUserActivityTimeoutOverrideFromWindowManager >= 0) {            timeout = (int)Math.min(timeout, mUserActivityTimeoutOverrideFromWindowManager);        }        nosleep = mScreenOffTimeoutSetting;        if(nosleep  < 0)        {            nosleep = mMaximumScreenOffTimeoutFromDeviceAdmin ;            return Math.max(nosleep, mMaximumScreenOffTimeoutFromDeviceAdmin);        }        return Math.max(timeout, MINIMUM_SCREEN_OFF_TIMEOUT);

修改后就不会休眠了。可能还有其它方法让其用不休眠，有兴趣的人可以在看看源码找着看。