IOS5 setBrightness无法与applicationWillResignActive一起使用

我使用 [[UIScreen mainScreen] setBrightness：] （在sdk 5.0中）更改我应用中的系统背景灯。

I use [[UIScreen mainScreen]setBrightness: ] (in sdk 5.0) to change the system background light in my app.

以下步骤适用于我的应用程序

The following steps work with my app

1. 激活应用程序，默认获取系统亮度，然后另存为 sysBright 。

使用我的应用更改亮度，更改亮度，然后另存为 appBright 。

Change the brightness with my app, changed brightness, then save as appBright.

带主页按钮或锁定按钮的ResignActive应用程序，将亮度设置为 sysBright （步骤1值，系统默认亮度）。

ResignActive app with home button or lock button, set brightness to sysBright (step 1 value, system default brightness).

再次激活应用程序。然后它将重复上述步骤形式1到3.

Active app again. Then it will repeat the above steps form 1 to 3.

第3步出现问题，当我取消激活时使用锁定按钮的应用程序，函数 applicationWillResignActive 效果很好，它可以恢复亮度值（ sysBright ）。

Something is wrong with step 3, when I inactivate the app with the lock button, the function applicationWillResignActive works well, it can restore the brightness value (sysBright).

但是当我按下主页按钮时，它不再起作用了。亮度仍然是我在我的应用程序中更改的值。 （ appBright ）

But when I press the home button, it doesn't work anymore. The brightness is still the value I changed in my app. (appBright)

有没有人知道它？感谢您的帮助〜

Does anyone have any idea about it? Thanks for any help ~

以下是代码：

float appBright,sysBright;

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    sysBright = [[UIScreen mainScreen] brightness];
    [[NSUserDefaults standardUserDefaults] setFloat:sysBright forKey:@"sysBright"];

    [[UIScreen mainScreen] setBrightness:appBright];
}

//doesn't work when i ResignActive with the home button
- (void)applicationWillResignActive:(UIApplication *)application
{        
    [[NSUserDefaults standardUserDefaults] floatForKey:@"sysBright"];
    [[UIScreen mainScreen] setBrightness:sysBright];        
}