很多人都認為UITextField很簡單，為什么會寫這個協議呢？
因為在實際開發中可能會用到；
比如要做到下圖的效果：
文本框下面的下劃線的顏色要隨著輸入的狀態變化；
點擊對應的文本框，其下面的線條變為綠色，結束編輯，變為灰色；
要熟悉UITextFieldDelegate協議才能做到這一點；
首先，先看一下官方的說明：
- (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;
文本框已經開始編輯
2、
- (void)textFieldDidEndEditing:(UITextField *)textField; 文本框已經結束編輯
3、其他設置是否允許的輸入控制
1、- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField; // return NO to disallow editing.
//控制是否允許輸入，返回值是NO的時候，禁止輸入；
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 //是否結束輸入，返回值是YES時候，允許停止輸入，并且釋放第一響應；返回NO的時候，則相反；3、- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string; // return NO to not change text
//是否改變輸入文本，返回NO的時候，不保存修改
4、- (BOOL)textFieldShouldClear:(UITextField *)textField; // called when clear button pressed. return NO to ignore (no notifications)
//當清空按鈕時候調用，返回是NO的時候，忽視清空
5、- (BOOL)textFieldShouldReturn:(UITextField *)textField; // called when 'return' key pressed. return NO to ignore.
//當點擊return按鈕時候調用該方法，返回是NO的時候，不做任何響應；
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