判断 iPhone 虚拟键盘是否打开的代码

CocoaChina 会员“qqn_pipi”分享的判断 iPhone 虚拟键盘是否打开的代码，原理很简单：看当前的窗口是否存在一个 responder，从而判别 iPhone 的键盘是否打开了。

BOOL TTIsKeyboardVisible() {
  // Operates on the assumption that the keyboard is visible if and only if there is a first
  // responder; i.e. a control responding to key events
  UIWindow* window = [UIApplication sharedApplication].keyWindow;
  return !![window findFirstResponder];
}