iOS QR界面亮度调整

亮度调事，不久在QR界面切换的时候还要考虑进入前台后台时的操作

1.QR界面功能实现代码。
QR界面 - (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated];
[[NSUserDefaults standardUserDefaults] setValue:@([UIScreen
mainScreen].brightness) forKey:@"Brightness"]; [UIScreen mainScreen].brightness
= 1; } - (void) viewWillDisappear:(BOOL)animated { [super
viewWillDisappear:animated]; NSNumber* num = [[NSUserDefaults
standardUserDefaults] objectForKey:@"Brightness"]; if(num.floatValue > 0.1) {
[UIScreen mainScreen].brightness = num.floatValue; } }
2.进入前后台时的处理。这个地方要意思，必须要在Appdelegate 

中的两个回调函数中实现，在QR()中添加进入前后台通知实现的话，会有问题。具体原历不清楚

- (void)applicationDidBecomeActive:(UIApplication *)application

- (void)applicationWillResignActive:(UIApplication *)application
- (void)applicationDidBecomeActive:(UIApplication *)application {
application.applicationIconBadgeNumber = 0; if(当前界面是QR界面） { [UIScreen
mainScreen].brightness = 1; } } -
(void)applicationWillResignActive:(UIApplication *)application { NSNumber* num
= [[NSUserDefaults standardUserDefaults] objectForKey:@"Brightness"];
if(num.floatValue > 0.1) { [UIScreen mainScreen].brightness = num.floatValue; }
NSLog(@"num = %@", num); }

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