键盘种类UIKeyboardType枚举：
UIKeyboardTypeDefault, // 默认键盘：支持所有字符
UIKeyboardTypeASCIICapable, // 支持ASCII的默认键盘
UIKeyboardTypeNumbersAndPunctuation, // 标准电话键盘，支持+*#等符号
UIKeyboardTypeURL, // URL键盘，有.com按钮；只支持URL字符
UIKeyboardTypeNumberPad, //数字键盘
UIKeyboardTypePhonePad, // 电话键盘
UIKeyboardTypeNamePhonePad, // 电话键盘，也支持输入人名字
UIKeyboardTypeEmailAddress, // 用于输入电子邮件地址的键盘
} UIKeyboardType;
键盘外观UIKeyboardAppearance枚举：
typedef enum {
UIKeyboardAppearanceDefault, // 默认外观：浅灰色
UIKeyboardAppearanceAlert, //深灰/石墨色
} UIKeyboardAppearance;
