很多人都认为UITextField很简单，为什么会写这个协议呢？
因为在实际开发中可能会用到；
比如要做到下图的效果：
文本框下面的下划线的颜色要随着输入的状态变化；
点击对应的文本框，其下面的线条变为绿色，结束编辑，变为灰色；
要熟悉UITextFieldDelegate协议才能做到这一点；
首先，先看一下官方的说明：
- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField;//return NO to disallow editing.- (void)textFieldDidBeginEditing:(UITextField *)textField;//became first responder- (BOOL)textFieldShouldEndEditing:(UITextField *)textField;//return YES to allow editing to stop and to resign first responder status. NO to disallow the editingsessionto end- (void)textFieldDidEndEditing:(UITextField *)textField;//may be called if forced even if shouldEndEditing returns NO (e.g. view removed from window) or endEditing:YES called- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;//return NO to not change text- (BOOL)textFieldShouldClear:(UITextField *)textField;//called when clear buttonPRessed. return NO to ignore (no notifications)- (BOOL)textFieldShouldReturn:(UITextField *)textField;//called when 'return' key pressed. return NO to ignore.
1、
- (void)textFieldDidBeginEditing:(UITextField *)textField;
文本框已经开始编辑
2、
- (void)textFieldDidEndEditing:(UITextField *)textField;
文本框已经结束编辑
3、其他设置是否允许的输入控制
1、- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField;//return NO to disallow editing.
//控制是否允许输入，返回值是NO的时候，禁止输入；
2、- (BOOL)textFieldShouldEndEditing:(UITextField *)textField;//return YES to allow editing to stop and to resign first responder status. NO to disallow the editing session to end//是否结束输入，返回值是YES时候，允许停止输入，并且释放第一响应；返回NO的时候，则相反；
3、- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;//return NO to not change text
//是否改变输入文本，返回NO的时候，不保存修改
4、- (BOOL)textFieldShouldClear:(UITextField *)textField;//called when clear button pressed. return NO to ignore (no notifications)
//当清空按钮时候调用，返回是NO的时候，忽视清空
5、- (BOOL)textFieldShouldReturn:(UITextField *)textField;//called when 'return' key pressed. return NO to ignore.
//当点击return按钮时候调用该方法，返回是NO的时候，不做任何响应；