UITextFieldDelegate协议

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 editing session to 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 button pressed. 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；