iOS 限制textField输入的长度

1.电话号码（带3-3-4效果）

1. //指定代理

    self.phoneTextField.delegate = self;

2.    //当编辑改变的时候，进行字符校验
       [self.phoneTextField addTarget:self action:@selector(reformatAsPhoneNumber:) forControlEvents:UIControlEventEditingChanged];
   

3. #pragma mark - 手机号码分隔
   /**
    *  3-3-4手机号码分隔
    */
   -(void)reformatAsPhoneNumber:(UITextField *)textField {
       //判断正确的光标位置
       NSUInteger targetCursorPostion = [textField offsetFromPosition:textField.beginningOfDocument toPosition:textField.selectedTextRange.start];
       NSString *phoneNumberWithoutSpaces = [self removeNonDigits:textField.text andPreserveCursorPosition:&targetCursorPostion];
       if([phoneNumberWithoutSpaces length] > 11) {
           //避免超过11位的输入
           [textField setText:_previousTextFieldContent];
           textField.selectedTextRange = _previousSelection;
           return;
       }
   
       NSString *phoneNumberWithSpaces = [self insertSpacesEveryFourDigitsIntoString:phoneNumberWithoutSpaces andPreserveCursorPosition:&targetCursorPostion];
   
       textField.text = phoneNumberWithSpaces;
       UITextPosition *targetPostion = [textField positionFromPosition:textField.beginningOfDocument offset:targetCursorPostion];
       [textField setSelectedTextRange:[textField textRangeFromPosition:targetPostion toPosition:targetPostion]];
   }
   
   /**
    *  除去非数字字符，确定光标正确位置
    *
    *  @param string         当前的string
    *  @param cursorPosition 光标位置
    *
    *  @return 处理过后的string
    */
   - (NSString *)removeNonDigits:(NSString *)string andPreserveCursorPosition:(NSUInteger *)cursorPosition {
       NSUInteger originalCursorPosition = *cursorPosition;
       NSMutableString *digitsOnlyString = [NSMutableString new];
   
       for (NSUInteger i=0; i<string.length; i++) {
           unichar characterToAdd = [string characterAtIndex:i];
   
           if(isdigit(characterToAdd)) {
               NSString *stringToAdd = [NSString stringWithCharacters:&characterToAdd length:1];
               [digitsOnlyString appendString:stringToAdd];
           }
           else {
               if(i<originalCursorPosition) {
                   (*cursorPosition)--;
               }
           }
       }
       return digitsOnlyString;
   }
   
   /**
    *  将空格插入我们现在的string 中，并确定我们光标的正确位置，防止在空格中
    *
    *  @param string         当前的string
    *  @param cursorPosition 光标位置
    *
    *  @return 处理后有空格的string
    */
   - (NSString *)insertSpacesEveryFourDigitsIntoString:(NSString *)string andPreserveCursorPosition:(NSUInteger *)cursorPosition{
       NSMutableString *stringWithAddedSpaces = [NSMutableString new];
       NSUInteger cursorPositionInSpacelessString = *cursorPosition;
   
       for (NSUInteger i=0; i<string.length; i++) {
           if(i>0){
               if(i==3 || i==7) {
                   [stringWithAddedSpaces appendString:@" "];
                   if(i<cursorPositionInSpacelessString) {
                       (*cursorPosition)++;
                   }
               }
           }
           unichar characterToAdd = [string characterAtIndex:i];
           NSString *stringToAdd = [NSString stringWithCharacters:&characterToAdd length:1];
           [stringWithAddedSpaces appendString:stringToAdd];
       }
       return stringWithAddedSpaces;
   }
   
   #pragma mark - UITextFieldDelegate
   
   -(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
       _previousSelection = textField.selectedTextRange;
       _previousTextFieldContent = textField.text;
       if ( textField == self.phoneHMDTextField &&range.location >= 11){
           return  NO;
       }else {
           return YES;
       }
   }
   

二：监听代理方法（这样可以在if里通过判断，做几个textfield的限制输入）

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

    if ( textField == self.phoneHMDTextField  && range.location >= 11){
        return  NO;
    }else {
        return YES;
    }
}

三：

  //指定代理

    self.phoneTextField.delegate = self;

    //当编辑改变的时候，进行字符校验

    [self.phoneTextField addTarget:self action:@selector(reformatAsPhoneNumber:) forControlEvents:UIControlEventEditingChanged];

//监听字符改变的方法

- (void)textFieldDidChange:(UITextField *)textField
{
    if (textField == self.textFieldName) {
        if (textField.text.length > 15) {
　　　　　　　　UITextRange *markedRange = [textField markedTextRange];
        　　　if (markedRange) {
           　　 return;
       　　　 }
            //Emoji占2个字符，如果是超出了半个Emoji，用15位置来截取会出现Emoji截为2半
        //超出最大长度的那个字符序列(Emoji算一个字符序列)的range
        NSRange range = [textField.text rangeOfComposedCharacterSequenceAtIndex:15];
            textField.text = [textField.text substringToIndex:range.location];
        }
    }
}