使用系统的方法设置，效果图如下：

效果图.png

部分初始化

    // 数据源
    _dataModelArray = [[NSMutableArray alloc] init];
    // 设置索引
    _charArray = [[NSMutableArray alloc] init];
    // 索引字体颜色
    _tableView.sectionIndexColor = [UIColor colorWithHexString:@"686a6c"];
    // 索引背景色
    _tableView.sectionIndexBackgroundColor = [UIColor clearColor];

数据源的添加

                for (char key = 'A'; key<='Z'; key++) {
            
                    NSArray * eachArray = [memberArrayDic objectForKey:[NSString stringWithFormat:@"%c",key]];
                    if (eachArray) {
                        // 添加索引
                        [_charArray addObject:[NSString stringWithFormat:@"%c",key]];
                        
                        NSMutableArray * eachModelArray = [[NSMutableArray alloc] init];
                        for (NSDictionary * dict in eachArray) {
                            GroupUserModel * model = [GroupUserModel yy_modelWithDictionary:dict];
                            [eachModelArray addObject:model];
                        }
                        [_dataModelArray addObject:eachModelArray];
                    }

                }
                
                NSArray * otherArray = memberArrayDic[@"#"];
                if (otherArray) {
                    [_charArray addObject:@"#"];
                    
                    NSMutableArray * otherModelArray = [[NSMutableArray alloc] init];
                    for (NSDictionary * dic in otherArray) {
                        GroupUserModel * model = [GroupUserModel yy_modelWithDictionary:dic];
                        [otherModelArray addObject:model];
                    }
                    
                    [_dataModelArray addObject:otherModelArray];
                }

UITableView设置

#pragma mark - UITableViewDelegate,UITableViewDataSource
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return [_dataModelArray count];
}
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {
    return 22;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [_dataModelArray[section] count];
}
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 55;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString * identifier = @"cell";
    GroupSettingUserCell * cell = [tableView dequeueReusableCellWithIdentifier:identifier];
    if (cell == nil) {
        cell = [[NSBundle mainBundle] loadNibNamed:@"GroupSettingUserCell" owner:self options:nil].firstObject;
    }
    
    GroupUserModel * model = _dataModelArray[indexPath.section][indexPath.row];
    cell.userName = model.chatName;
    if ([model.selectedType isEqualToString:@"1"]) {
        cell.isSelected = YES;
    } else {
        cell.isSelected = NO;
    }
    return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    [tableView deselectRowAtIndexPath:indexPath animated:YES];
    
    GroupUserModel * model = _dataModelArray[indexPath.section][indexPath.row];
    if ([model.selectedType isEqualToString:@"0"]) {
        model.selectedType = @"1";
        _selectedUserCount ++;
    } else {
        model.selectedType = @"0";
        if (_selectedUserCount) {
            _selectedUserCount --;
        }
    }
    _upView.selectedCount = _selectedUserCount;
    [_tableView reloadData];
}
// 索引
- (NSArray<NSString *> *)sectionIndexTitlesForTableView:(UITableView *)tableView {
    return _charArray;
}
- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index {
    NSLog(@"===%@  ===%ld",title,(long)index);
    
    //点击索引，列表跳转到对应索引的行
    [tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:index]
                     atScrollPosition:UITableViewScrollPositionTop animated:YES];
    
    return index;
}
- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {

    UIView *headView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, 22)];
    headView.backgroundColor = [UIColor colorWithHexString:@"ebebeb"];

    //标题文字
    UILabel * title = [[UILabel alloc] initWithFrame:CGRectMake(15, 0, 40, 22)];
    title.backgroundColor = [UIColor clearColor];
    title.font = [UIFont systemFontOfSize:12];
    title.textColor = [UIColor colorWithHexString:@"a2a4a7"];
    title.text = _charArray[section];
    [headView addSubview:title];
    
    return headView;
}