iOS 键盘初始化的过程有短暂延迟

http://stackoverflow.com/a/9850093

因为某种原因，当app以调试模式第一次在机上运行的时候就会出现这个情况。在release模式下不会有延迟。

http://stackoverflow.com/a/20436797

对于每次运行都出现延迟，下面一段代码可能有用：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {  // Preloads keyboard so there's no lag on initial keyboard appearance.  UITextField *lagFreeField = [[UITextField alloc] init];  [self.window addSubview:lagFreeField];  [lagFreeField becomeFirstResponder];  [lagFreeField resignFirstResponder];  [lagFreeField removeFromSuperview];｝