对具有多个值的核心数据进行排序

Question

我有存储在 Core Data 中的品牌列表，每个品牌都与多个内容相关联。内容有一个名为downStatus 的标志，用于表示是否下载了内容。以下方法用于从 Core 数据中获取按品牌名称排序的所有品牌

-(void)getDownloadedBrands{

AppDelegate *aAppDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

NSMutableArray *aBrands = [[NSMutableArray alloc] init];


NSEntityDescription *entity =
[NSEntityDescription entityForName:@"Brand" inManagedObjectContext:aAppDelegate.managedobjectcontext];
 NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];

NSSortDescriptor *sort=[[NSSortDescriptor alloc]initWithKey:@"brandName" ascending:YES];
//NSSortDescriptor *sort1=[[NSSortDescriptor alloc]initWithKey:@"downStatus" ascending:YES];

[request setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];

aBrands =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request error:nil];
[request release];
[sort release];
NSLog(@"%@",aBrands);

brands = [[NSMutableArray alloc]initWithArray:aBrands];

aAppDelegate.dbBrandArr = brands;

[self loadGridView];

}

现在我想使用内容中的downStatus 进行排序。因此，就像按字母顺序下载的品牌，然后按字母顺序未下载的品牌。 downStatus 采用两个值 1 表示已下载 0 表示未下载。请帮忙。

Answer 1

一种方法是使用带有值1/0 on downStatus 属性的NSPredicate 将2 fetchRequests 转换为CoreData，并使用相同的字母顺序sortDescriptor。

现在通过将 0 数组添加到 1 数组来创建一个新数组。在您的代码中，它看起来像这样：

-(void)getDownloadedBrands{
    AppDelegate *aAppDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

    //2 arrays
    NSMutableArray *aBrands0 = [[NSMutableArray alloc] init];
    NSMutableArray *aBrands1 = [[NSMutableArray alloc] init];
    //set entity en make requests
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Brand" inManagedObjectContext:aAppDelegate.managedobjectcontext];
    NSFetchRequest *request0 = [[NSFetchRequest alloc] init];
    NSFetchRequest *request1 = [[NSFetchRequest alloc] init];
    [request0 setEntity:entity];
    [request1 setEntity:entity];
    //create sortDescriptor alphabetically
    NSSortDescriptor *sort=[[NSSortDescriptor alloc]initWithKey:@"brandName" ascending:YES];
    //create predicates on downStatus property
    NSPredicate *predicate0 = [NSPredicate predicateWithFormat:@"downStatus == %@", [NSNumber numberWithBool:0]];
    NSPredicate *predicate1 = [NSPredicate predicateWithFormat:@"downStatus == %@", [NSNumber numberWithBool:1]];
    //set predicates to the requests
    [request0 setPredicate:predicate0];
    [request1 setPredicate:predicate1];
    //set sortDescriptor to both requests
    [request0 setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];
    [request1 setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];
    //fetch arrays with downStatus 1/0
    aBrands0 =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request0 error:nil];
    aBrands1 =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request1 error:nil];
    //release requests // NOT USING ARC??
    [request0 release];
    [request1 release];
    [sort release];
    //log results
    NSLog(@"aBrands0: %@",aBrands0);
    NSLog(@"aBrands1: %@",aBrands1);
    //add object 0 array to 1 array
    NSArray *combinedArray = [aBrands1 arrayByAddingObjectsFromArray:aBrands0];
    //copy array to brands
    brands = [[NSMutableArray alloc]initWithArray:combinedArray];
    //set property on appDelegate
    aAppDelegate.dbBrandArr = brands;
    //reload tableView
    [self loadGridView];
}

-- 编辑，使用 downStatus 键为 NSDictionary 添加答案

-(void)getDownloadedBrands{
    AppDelegate *aAppDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

    NSMutableArray *aBrands = [[NSMutableArray alloc] init];


    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Brand" inManagedObjectContext:aAppDelegate.managedobjectcontext];
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entity];

    NSSortDescriptor *sort=[[NSSortDescriptor alloc]initWithKey:@"brandName" ascending:YES];
    //NSSortDescriptor *sort1=[[NSSortDescriptor alloc]initWithKey:@"downStatus" ascending:YES];

    [request setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];

    aBrands =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request error:nil];

    NSMutableArray *aBrands0 = [[NSMutableArray alloc] init];
    NSMutableArray *aBrands1 = [[NSMutableArray alloc] init];
    for (NSDictionary *dict in aBrands) {
        if ([dict valueForKeyPath:@"downStatus"] == YES)
        {
            //add to 1 array
            [aBrands1 addObject:dict];
        }
        else
        {
            //add to 0 array
            [aBrands0 addObject:dict];
        }
    }

    //sort arrays
    NSArray * array1 = [aBrands1 sortedArrayUsingDescriptors:[NSArray arrayWithObject:sort]];
    NSArray * array0 = [aBrands0 sortedArrayUsingDescriptors:[NSArray arrayWithObject:sort]];
    NSArray * allArray = [aBrands1 arrayByAddingObjectsFromArray:aBrands0];

    //combine arrays

    //copy array to brands
    brands = [[NSMutableArray alloc]initWithArray:combinedArray];
    //set property on appDelegate
    aAppDelegate.dbBrandArr = brands;
    //reload tableView
    [self loadGridView];

    [request release];
    [sort release];
    NSLog(@"%@",aBrands);
}

Answer 2

如果您打算在 UITableViewController 中使用获取结果，则可以将 fetchedResultsController 的 sectionNameKeyPath 用于 downStatus，并保留品牌名称的排序描述符。可以是这样的：

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext
sectionNameKeyPath:@"customSectionTitle" cacheName:nil];

把它放在你的 NSManagedObject 的头文件中：

-(NSString*)customSectionTitle;

这在 .m 中：

-(NSString*)customSectionTitle{
    if ([downStatus boolValue] == YES) {
        return @"Downloaded";
    }
    else {return @"Not Downloaded";}
}

如果您不打算使用 fetchedResultsController，只需先按 downStatus 排序，然后按品牌名称。