ios - Objective C 创建未知大小的二维数组并访问它

Question

我对 Objective-C 还是个新手。我想创建一个未知大小的二维数组，以便我可以访问它并添加值。我来自 C++ 背景并查看教程点和示例，例如 Declaring and Initializing 2D array of unknown size in C看起来 C++ 和 Objective C 在创建二维数组方面有相似之处。

我实现了以下示例，但出现错误:

由于未捕获的异常“NSRangeException”而终止应用程序，原因:“* -[__NSArrayM objectAtIndex:]:索引 0 超出空数组的范围”**

我不确定是什么导致了这个错误，如果能帮助我解决这个错误并理解它，我将不胜感激。

-(NSMutableArray *)categoryCk
{
    if (!_categoryCk)
    {
        _categoryCk = [[NSMutableArray alloc] init];
    }
    return _categoryCk;
}
-(NSMutableArray *)subcategoryCv
{
    if (!_subcategoryCv)
    {
        _subcategoryCv = [[NSMutableArray alloc] init];
    }
    return _subcategoryCv;
}

-(NSMutableArray *)subcategoryCk
{
    if (!_subcategoryCk)
    {
         _subcategoryCk = [[NSMutableArray alloc] init];
    }
    return _subcategoryCk;
}
-(NSMutableArray *)outcomeCv
{
    if (!_outcomeCv)
    {
        _outcomeCv = [[NSMutableArray alloc] init];
    }
    return _outcomeCv;
}

-(NSMutableArray *)outcomeCk
{
    if (!_outcomeCk)
    {
        _outcomeCk = [[NSMutableArray alloc] init];
    }
    return _outcomeCk;
}

然后循环创建数组:

if([categories count]>0){

    for (int i =0; i < categories.count; i++)

    {
        NSArray* subCategories= [categories[i] objectForKey: @"subCategories"];


        NSDictionary *categoryItems = [categories objectAtIndex:i];
        NSString *category = [categoryItems objectForKey:@"cv"];
        NSLog(@"%@",category);
        [self.categoryCv addObject:category];
        NSString *categoryNum = [categoryItems objectForKey:@"ck"];
        [self.categoryCk addObject:categoryNum];

        if ([subCategories count] > 0){

        for (int j = 0; j < subCategories.count; j++) {

            if (self.subcategoryCv.count <= i) {
                [self.subcategoryCv addObject:[[NSMutableArray alloc] init]];
            }

            if ([self.subcategoryCv[i] count] <= j) {
                [self.subcategoryCv[i] addObject:[[NSMutableArray alloc] init]];
            }
            if (self.subcategoryCk.count <= i) {
                [self.subcategoryCk addObject:[[NSMutableArray alloc] init]];
            }

            if ([self.subcategoryCk[i] count] <= j) {
                [self.subcategoryCk[i] addObject:[[NSMutableArray alloc] init]];
            }

            NSDictionary *subcategoryItems = [subCategories objectAtIndex:j];
            NSString *subCategoryCv = [subcategoryItems objectForKey:@"cv"];
            [self.subcategoryCv[i][j] addObject:subCategoryCv];
            NSString *subCatNum = [subcategoryItems objectForKey:@"ck"];
            [self.subcategoryCk[i][j] addObject:subCatNum];

            NSArray* outcome =[[subCategories objectAtIndex:j] objectForKey:@"outcomes"];

            if ([outcome count] > 0) {

            for (int k = 0; k < outcome.count; k++) {

                if (self.outcomeCv.count <= j) {
                    [self.outcomeCv addObject:[[NSMutableArray alloc] init]];
                }

                if ([self.outcomeCv[j] count] <= k) {
                    [self.outcomeCv[j] addObject:[[NSMutableArray alloc] init]];
                }


                if (self.outcomeCk.count <= j) {
                    [self.outcomeCk addObject:[[NSMutableArray alloc] init]];
                }

                if ([self.outcomeCk[j] count] <= k) {
                    [self.outcomeCk[j] addObject:[[NSMutableArray alloc] init]];
                }

                NSDictionary *outComeItems = [outcome objectAtIndex:k];
                NSString *outcomeCategoryCV = [outComeItems objectForKey:@"cv"];
                //NSLog(@"%@",outcomeCatCV);
                [self.outcomeCv[j][k] addObject:outcomeCategoryCV];
                NSString *outCatNum = [outComeItems objectForKey:@"ck"];
                [self.outcomeCk[j][k] addObject:outCatNum];

            }
            }else{

            UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"Alert"
                                                                               message:@"Error loading data from service : Empty Outcomes data"
                                                                        preferredStyle:UIAlertControllerStyleAlert];

            UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
                                                                      handler:^(UIAlertAction * action) {}];

            [alert addAction:defaultAction];
            [self presentViewController:alert animated:YES completion:nil];

            }
        }
        } else{

            UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"Alert"
                                                                           message:@"Error loading data from service : Empty Sub-Categories data"
                                                                    preferredStyle:UIAlertControllerStyleAlert];

            UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
                                                                  handler:^(UIAlertAction * action) {}];

            [alert addAction:defaultAction];
            [self presentViewController:alert animated:YES completion:nil];
        }
    }

}else{

    UIAlertController* alert = [UIAlertController alertControllerWithTitle:@"Alert"
                                                                   message:@"Error loading data from service : Empty Categories data"
                                                            preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault
                                                          handler:^(UIAlertAction * action) {}];

    [alert addAction:defaultAction];
    [self presentViewController:alert animated:YES completion:nil];

}

这就是我尝试访问数组的方式:

 cell.textLabel.text = [self.outcomeCv[categoryIndex][subcategoryIndex] objectAtIndex:indexPath.row] ;

Answer 1

当您调用 subcategoryCv[i][j] 时，你必须确保

subcategoryCv.count > i && subcategoryCv[i].count > j

否则，你的问题会崩溃。

为了防止它，你需要添加一个新的NSMutableArray至 subcategoryCv什么时候subcategoryCv.count <= i并添加一个新的 NSMutableArray至 subcategoryCv[i]什么时候subcategoryCv[i].count <= j .

另一个二维数组也是一样。例如 subcategoryCv

if (self.subcategoryCv.count <= i) {
  [self.subcategoryCv addObject:[[NSMutableArray alloc] init]];
}

if ([self.subcategoryCv[i] count] <= j) {
  [self.subcategoryCv[i] addObject:[[NSMutableArray alloc] init]];
}

NSDictionary *subcategoryItems = [subCategories objectAtIndex:j];
NSString *subCategoryCv = [subcategoryItems objectForKey:@"cv"];
[self.subcategoryCv[i][j] addObject:subCategoryCv];
NSString *subCatNum = [subcategoryItems objectForKey:@"ck"];
[self.subcategoryCk[i][j] addObject:subCatNum];