修改[UIScreen mainScreen].brightness值是在子线程修改导致崩溃，需要回到主线程后再修改brightness

[iimuy]

修改代码如下
[_queue addOperationWithBlock:^{
[NSThread sleepForTimeInterval:1 / 180.0];
dispatch_async(dispatch_get_main_queue(), ^{
[UIScreen mainScreen].brightness = brightness + i * step;
});
}];