TableView 加索引

给 TableView 加索引的方法不必多说，但有的 TableView 会显示其指向内容为空的索引，如官方自带的通讯录这样：

所谓的非空索引指的是当索引所指向的 section 内容为空时，不添加这条索引，如图：

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话不多说，上代码：

省份的模型：

@interface State : NSObject
@property(nonatomic,copy) NSString *name;
@property NSInteger sectionNumber;
@end

加载 plist 中的内容，将其转换为一个二维数组，并在其中用官方的 UILocalizedIndexedCollation 将数组按拼音的字母顺序排序，这里只添加不为空的数组，保证索引都不为空。

- (NSMutableArray *)states
{
    if (_states == nil) {
        _states = [NSMutableArray arrayWithCapacity:1];

        NSString *thePath = [[NSBundle mainBundle] pathForResource:@"ProvincesAndCities" ofType:@"plist"];
        NSArray *tempArray;
        NSMutableArray *statesTemp;
        if (thePath && (tempArray = [NSArray arrayWithContentsOfFile:thePath])) {
            statesTemp = [NSMutableArray arrayWithCapacity:1];
            for (NSDictionary *stateDict in tempArray) {
                State *aState = [[State alloc] init];
                aState.name = [stateDict objectForKey:@"State"];
                [statesTemp addObject:aState];
            }
        }else{
            return nil;
        }

        UILocalizedIndexedCollation *theCollation = [UILocalizedIndexedCollation currentCollation];

        //1\. 将 state 按其属性 name 的拼音顺序排序
        for (State *theState in statesTemp) {
            NSInteger sect = [theCollation sectionForObject:theState collationStringSelector:@selector(name)];
            theState.sectionNumber = sect;
        }

        //2\. 创建一个二维数组
        NSInteger highSection = [[theCollation sectionTitles] count];
        NSMutableArray *sectionArrays = [NSMutableArray arrayWithCapacity:highSection];
        for (int i = 0; i < highSection; i++) {
            NSMutableArray *sectionArray = [NSMutableArray arrayWithCapacity:1];
            [sectionArrays addObject:sectionArray];
        }

        //3\. 将 state 按序号加入组中
        for (State *theState in statesTemp) {
            [(NSMutableArray *)[sectionArrays objectAtIndex:theState.sectionNumber] addObject:theState];
        }

        //4\. 组内排序
        for (NSMutableArray *sectionArray in sectionArrays) {
            if ([sectionArray count] > 0) {
                NSArray *sortedSection = [theCollation sortedArrayFromArray:sectionArray
                                                    collationStringSelector:@selector(name)];
                [_states addObject:sortedSection];
            }
        }
    }
    return _states;
}

UILocalizedIndexedCollation 默认从0开始，指向从A到Z的数据，之前删除掉了为空的字母，这里需要重新将字母顺序与字母对应起来。

- (NSMutableArray *)letterArray
{
    if (_letterArray == nil) {
        _letterArray = [NSMutableArray arrayWithCapacity:[self.states count]];
        NSArray *letterArr = @[@"A",@"B",@"C",@"D",@"E",@"F",@"G",@"H",@"I",@"J",
                               @"K",@"L",@"M",@"N",@"O",@"P",@"Q",@"R",@"S",@"T",
                               @"U",@"V",@"W",@"X",@"Y",@"Z"];
        for (NSMutableArray *array in self.states) {
            if ([array count] > 0) {
                State *tmpState = array[0];
                [_letterArray addObject:[letterArr objectAtIndex:tmpState.sectionNumber]];
            }
        }
    }
    return _letterArray;
}

TableView 的代理方法：

//返回索引数组
- (NSArray<NSString *> *)sectionIndexTitlesForTableView:(UITableView *)tableView
{
    return self.letterArray;
}

//当点击索引时，跳转到对应的section
- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
{
    return [[UILocalizedIndexedCollation currentCollation] sectionForSectionIndexTitleAtIndex:index];
}

//返回 section 标题
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    return [self.letterArray objectAtIndex:section];
}