UITextField上的iPhone虚拟键盘弹出缓慢点击

Question

触摸UITextField后弹出键盘需要2-3秒。

我试过了：

- (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];
}

当我搜索SO时似乎正在工作。但这对我不起作用。任何帮助将不胜感激。