textField 视图的上升/下降 => 用协议方法控制

• 遵守代理，实现以下方法。

// 开始编辑
- (void)textFieldDidBeginEditing:(UITextField *)textField {

	// 获取当前视图的 frame
	CGRect frame = self.view.frame;
	frame.origin.y = -53;

	[UIView animateWithDuration:0.5 animations:^{
		self.view.frame = frame;
	}];
}

// 结束编辑
- (void)textFieldDidEndEditing:(UITextField *)textField {

	CGRect frame = self.view.frame;
	frame.origin.y = 0;

	[UIView animateWithDuration:0.5 animations:^{
		self.view.frame = frame;
	}];
}