ios - SortedArrayUsingSelector 无法识别的选择器

Question

我是 ios 的新手，我真的很难找到解决这个问题的方法......

    animals = @{@"B" : @[@"Bear", @"Black Swan", @"Buffalo"],
            @"C" : @[@"Camel", @"Cockatoo"],
            @"D" : @[@"Dog", @"Donkey"],
            @"E" : @[@"Emu"],
            @"G" : @[@"Giraffe", @"Greater Rhea"],
            @"H" : @[@"Hippopotamus", @"Horse"],
            @"K" : @[@"Koala"],
            @"L" : @[@"Lion", @"Llama"],
            @"M" : @[@"Manatus", @"Meerkat"],
            @"P" : @[@"Panda", @"Peacock", @"Pig", @"Platypus", @"Polar Bear"],
            @"R" : @[@"Rhinoceros"],
            @"S" : @[@"Seagull"],
            @"T" : @[@"Tasmania Devil"],
            @"W" : @[@"Whale", @"Whale Shark", @"Wombat"]};
    animalSectionTitles = [[animals allKeys] sortedArrayUsingSelector:@selector(compare:)];

上面的代码没有错误，但是当我尝试将数组插入 NSDictionary 时，它总是显示无法识别的选择器。我应该怎么做才能解决这个问题？

while (sqlite3_step(statement)==SQLITE_ROW) {
        Word *univer = [[Word alloc] init];
        univer.Id =[NSString stringWithUTF8String:(char *) sqlite3_column_text(statement,0)];
        univer.word=[NSString stringWithUTF8String:(char *) sqlite3_column_text(statement,1)];
        //NSLog(@"%@",univer.word);
        NSString *first = [univer.word substringToIndex:1];
        NSLog(@"%@",first);
        if([first isEqualToString:@"A"] || [first isEqualToString:@"a"]){
            [_A addObject:univer.word];
        }
        else if([first isEqualToString:@"B"] || [first isEqualToString:@"b"]){
            [_B addObject:univer.word];
        }
        else if([first isEqualToString:@"C"] || [first isEqualToString:@"c"]){
            [_C addObject:univer.word];
        }
        else if([first isEqualToString:@"D"] || [first isEqualToString:@"d"]){
            [_D addObject:univer.word];
        }
        else if([first isEqualToString:@"E"] || [first isEqualToString:@"e"]){
            [_E addObject:univer.word];
        }
        else if([first isEqualToString:@"F"] || [first isEqualToString:@"f"]){
            [_F addObject:univer.word];
        }
        else if([first isEqualToString:@"G"] || [first isEqualToString:@"g"]){
            [_G addObject:univer.word];
        }
        else if([first isEqualToString:@"H"] || [first isEqualToString:@"h"]){
            [_H addObject:univer.word];
        }
    }
animals= [NSDictionary dictionaryWithObjectsAndKeys:_A,_B,_C,_D,_E,_F,_G,_H, nil];
animalSectionTitles = [[animals allKeys] sortedArrayUsingSelector:@selector(compare:)];

Answer 1

问题是这一行:

animals= [NSDictionary dictionaryWithObjectsAndKeys:_A,_B,_C,_D,_E,_F,_G,_H, nil];

当您使用 dictionaryWithObjectsAndKeys: 创建字典时，您提供的项目列表必须是 objectA, keyA, objectB, keyB, objectC, keyC, nil。现在看起来你只有 objectA, objectB, objectC, nil。如果你把它写出来，它看起来像这样:

animals = @{@[@"Bear", @"Black Swan", @"Buffalo"] : @[@"Camel", @"Cockatoo"],
            @[@"Dog", @"Donkey"] : @[@"Emu"],
            @[@"Giraffe", @"Greater Rhea"] : @[@"Hippopotamus", @"Horse"]};

当您调用 [[animals allKeys] sortedArrayUsingSelector:@selector(compare:)] 时，它会在 [ animals allKeys] 是 NSArray，不支持 compare: 方法，因此出现无法识别的选择器错误。

不确定你到底想要什么，但试试这个:

animals= [NSDictionary dictionaryWithObjectsAndKeys:_A, @"A", _B, @"B", _C, @"C", nil];