原文：https://www.jianshu.com/p/c97f9206226c

    [phoneTF addTarget:self action:@selector(phoneNumChange:) forControlEvents:UIControlEventEditingChanged]; // 监听改变

定义属性

NSString *previousTextFieldContent;
    UITextRange *previousSelection;

监听方法 和 代理方法

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    previousTextFieldContent = textField.text;
    previousSelection = textField.selectedTextRange;
return YES;
}

-(void)phoneNumChange:(id)sender{


    UITextField *textField = (UITextField *)sender;

    //限制手机账号长度13位（有两个空格）
    if (textField.text.length > 13) {
        textField.text = [textField.text substringToIndex:13];
    }

    NSUInteger targetCursorPosition = [textField offsetFromPosition:textField.beginningOfDocument toPosition:textField.selectedTextRange.start];

    NSString *currentStr = [textField.text stringByReplacingOccurrencesOfString:@" " withString:@""];
    NSString *preStr = [previousTextFieldContent stringByReplacingOccurrencesOfString:@" " withString:@""];

    //正在执行删除操作时为0，否则为1
    char editFlag = 0;
    if (currentStr.length <= preStr.length) {
        editFlag = 0;
    }else{
        editFlag = 1;
    }


    NSMutableString *tempStr = [NSMutableString new];

    int spaceCount = 0;
    if (currentStr.length < 3 && currentStr.length > -1) {
        spaceCount = 0;
    }else if (currentStr.length < 7 && currentStr.length > 2) {
        spaceCount = 1;
    }else if (currentStr.length < 12 && currentStr.length > 6) {
        spaceCount = 2;
    }

    for (int i = 0; i < spaceCount; i++) {
        if (i == 0) {
            [tempStr appendFormat:@"%@%@", [currentStr substringWithRange:NSMakeRange(0, 3)], @" "];
        }else if (i == 1) {
            [tempStr appendFormat:@"%@%@", [currentStr substringWithRange:NSMakeRange(3, 4)], @" "];
        }else if (i == 2) {
            [tempStr appendFormat:@"%@%@", [currentStr substringWithRange:NSMakeRange(7, 4)], @" "];
        }
    }

    if (currentStr.length == 11) {
        [tempStr appendFormat:@"%@%@", [currentStr substringWithRange:NSMakeRange(7, 4)], @" "];
    }
    if (currentStr.length < 4) {
        [tempStr appendString:[currentStr substringWithRange:NSMakeRange(currentStr.length - currentStr.length % 3, currentStr.length % 3)]];
    }else if(currentStr.length > 3 && currentStr.length <12) {
        NSString *str = [currentStr substringFromIndex:3];
        [tempStr appendString:[str substringWithRange:NSMakeRange(str.length - str.length % 4, str.length % 4)]];
        if (currentStr.length == 11) {
            [tempStr deleteCharactersInRange:NSMakeRange(13, 1)];
        }
    }
    textField.text = tempStr;
    // 当前光标的偏移位置
    NSUInteger curTargetCursorPosition = targetCursorPosition;

    if (editFlag == 0) {
        //删除
        if (targetCursorPosition == 9 || targetCursorPosition == 4) {
            curTargetCursorPosition = targetCursorPosition - 1;
        }
    }else {
        //添加
        if (currentStr.length == 8 || currentStr.length == 4) {
            curTargetCursorPosition = targetCursorPosition + 1;
        }
    }
    UITextPosition *targetPosition = [textField positionFromPosition:[textField beginningOfDocument] offset:curTargetCursorPosition];
    [textField setSelectedTextRange:[textField textRangeFromPosition:targetPosition toPosition :targetPosition]];

}