UItextField：
一、UItextField概念：
UItextField通常用于外部数据输入，以实现人机交互。下面以一个简单的登陆界面来讲解UItextField的详细使用。
二、UItextField的初始化：
eg: UITextField *tf = [[UITextField alloc]init];
tf.frame = CGRectMake(100, 100, 200, 50);
tf.delegate = self;
tf.backgroundColor = [UIColor orangeColor];
//更改提示信息内容
tf.placeholder = @"请输入用户名";
//更改return显示效果
/*
UIReturnKeyDefault, -默认效果
UIReturnKeyGo, -开始
UIReturnKeyGoogle, -搜索
UIReturnKeyJoin, -加入
UIReturnKeyNext, -下一步
UIReturnKeySearch, -搜索
UIReturnKeySend, -发送
UIReturnKeyYahoo, -日本
UIReturnKeyDone, -结束
UIReturnKeyEmergencyCall,
*/
tf.returnKeyType = UIReturnKeyDone;
//外观样式
/**
UIKeyboardAppearanceDefault, // Default apperance for the current input method.
UIKeyboardAppearanceDark NS_ENUM_AVAILABLE_IOS(7_0),
UIKeyboardAppearanceLight NS_ENUM_AVAILABLE_IOS(7_0),
UIKeyboardAppearanceAlert
*/
tf.keyboardAppearance = UIKeyboardAppearanceDefault;
//键盘类型
/**
UIKeyboardTypePhonePad - 电话键盘
UIKeyboardTypeNumberPad - 纯数字
UIKeyboardTypeEmailAddress - email地址键盘
*/
tf.keyboardType = UIKeyboardTypeASCIICapable;
//秘密输入
tf.secureTextEntry = YES;
//清空按键出现的时机
tf.clearButtonMode = UITextFieldViewModeAlways;
/**
UITextBorderStyleNone, -默认
UITextBorderStyleLine, -直线框
UITextBorderStyleRoundedRect -曲线框
*/
tf.borderStyle = UITextBorderStyleRoundedRect;
//必写
-(BOOL)textFieldShouldReturn:(UITextField *)textField
{
//取消键盘的第一相应，键盘收回
[textField resignFirstResponder];
return YES;
}
//- (BOOL)textFieldShouldClear:(UITextField *)textField
//-(void)textFieldDidEndEditing:(UITextField *)textField
//-(void)textFieldDidBeginEditing:(UITextField *)textField
//-(BOOL)textFieldShouldReturn:(UITextField *)textField
//-(BOOL)textFieldShouldEndEditing:(UITextField *)textField
//-(BOOL)textFieldShouldBeginEditing:(UITextField *)textField
//用来控制输入内容的
//-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
