代码之家 › 专栏 › 技术社区 › Greg Combs

NSFetchedResultsController,其节由字符串的第一个字母创建

core-data objective-c ios iphone

Greg Combs · 技术社区 · 16 年前

在iPhone上学习核心数据。关于核心数据用节填充表视图的例子似乎很少。这个 CoreDataBooks 示例使用节,但它们是从模型中的完整字符串生成的。我想把核心数据表按姓氏的第一个字母(地址簿的第一个字母)组织成几个部分。

我可以进去为每个人创建另一个属性,即一个字母,以充当分区,但这似乎很困难。

这是我的开始。。。这个把戏似乎在愚弄观众 sectionNameKeyPath

- (NSFetchedResultsController *)fetchedResultsController {
//.........SOME STUFF DELETED
    // Edit the sort key as appropriate.
    NSSortDescriptor *orderDescriptor = [[NSSortDescriptor alloc] initWithKey:@"personName" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:orderDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];
    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = 
            [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
            managedObjectContext:managedObjectContext 
            sectionNameKeyPath:@"personName" cacheName:@"Root"];
//....
}

7 回复 | 直到 13 年前

Stuart 16 年前

戴夫·德隆的方法是好的,至少在我的情况下,只要你忽略了几件事。以下是它对我的作用:

到名为 “lastnamepinitial”(或其他类似的词)

使此属性为瞬态。这将其保存到数据文件中。这当你需要的时候。

实体

不要为这个担心二传手所有物创建此getter(这是一半的魔法,伊姆霍)

// THIS ATTRIBUTE GETTER GOES IN YOUR OBJECT MODEL
- (NSString *) committeeNameInitial {
    [self willAccessValueForKey:@"committeeNameInitial"];
    NSString * initial = [[self committeeName] substringToIndex:1];
    [self didAccessValueForKey:@"committeeNameInitial"];
    return initial;
}


// THIS GOES IN YOUR fetchedResultsController: METHOD
// Edit the sort key as appropriate.
NSSortDescriptor *nameInitialSortOrder = [[NSSortDescriptor alloc] 
        initWithKey:@"committeeName" ascending:YES];

[fetchRequest setSortDescriptors:[NSArray arrayWithObject:nameInitialSortOrder]];

NSFetchedResultsController *aFetchedResultsController = 
        [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
        managedObjectContext:managedObjectContext 
        sectionNameKeyPath:@"committeeNameInitial" cacheName:@"Root"];

以前:按照Dave的初始步骤,在setPropertiesToFetch出现无效参数异常时,该字母会因setPropertiesToFetch而消失。我已将代码和调试信息记录在下面:

NSDictionary * entityProperties = [entity propertiesByName];
NSPropertyDescription * nameInitialProperty = [entityProperties objectForKey:@"committeeNameInitial"];
NSArray * tempPropertyArray = [NSArray arrayWithObject:nameInitialProperty];

//  NSARRAY * tempPropertyArray RETURNS:
//    <CFArray 0xf54090 [0x30307a00]>{type = immutable, count = 1, values = (
//    0 : (<NSAttributeDescription: 0xf2df80>), 
//    name committeeNameInitial, isOptional 1, isTransient 1,
//    entity CommitteeObj, renamingIdentifier committeeNameInitial, 
//    validation predicates (), warnings (), versionHashModifier (null), 
//    attributeType 700 , attributeValueClassName NSString, defaultValue (null)
//    )}

//  NSInvalidArgumentException AT THIS LINE vvvv
[fetchRequest setPropertiesToFetch:tempPropertyArray];

//  *** Terminating app due to uncaught exception 'NSInvalidArgumentException',
//    reason: 'Invalid property (<NSAttributeDescription: 0xf2dfb0>), 
//    name committeeNameInitial, isOptional 1, isTransient 1, entity CommitteeObj, 
//    renamingIdentifier committeeNameInitial, 
//    validation predicates (), warnings (), 
//    versionHashModifier (null), 
//    attributeType 700 , attributeValueClassName NSString, 
//    defaultValue (null) passed to setPropertiesToFetch: (property is transient)'

[fetchRequest setReturnsDistinctResults:YES];

NSSortDescriptor * nameInitialSortOrder = [[[NSSortDescriptor alloc]
    initWithKey:@"committeeNameInitial" ascending:YES] autorelease];

[fetchRequest setSortDescriptors:[NSArray arrayWithObject:nameInitialSortOrder]];

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] 
    initWithFetchRequest:fetchRequest 
    managedObjectContext:managedObjectContext 
    sectionNameKeyPath:@"committeeNameInitial" cacheName:@"Root"];

Greg Combs 13 年前

我想我还有另一个选择,这个选择使用了NSString上的一个类别。。。

@implementation NSString (FetchedGroupByString)
- (NSString *)stringGroupByFirstInitial {
    if (!self.length || self.length == 1)
        return self;
    return [self substringToIndex:1];
}
@end

稍后,在构建FRC时:

- (NSFetchedResultsController *)newFRC {
    NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:awesomeRequest
            managedObjectContext:coolManagedObjectContext
            sectionNameKeyPath:@"lastName.stringGroupByFirstInitial"
            cacheName:@"CoolCat"];
    return frc;
}

Dave DeLong 16 年前

这就是你的想法可以让它工作起来:

使此属性为瞬态。这意味着核心数据不会麻烦地保存到您的数据文件中。此属性仅在需要时存在于内存中。
生成此实体的类文件。

- (NSString *) lastNameInitial {

     [self willAccessValueForKey:@"lastNameInitial"];

     NSString * initial = [[self lastName] substringToIndex:1];

     [self didAccessValueForKey:@"lastNameInitial"];

     return initial;

}

在fetch请求中,仅请求此PropertyDescription,如下所示(这是另一个神奇之处):

NSDictionary * entityProperties = [myEntityDescription propertiesByName];

NSPropertyDescription * lastNameInitialProperty = [entityProperties objectForKey:@"lastNameInitial"];

[fetchRequest setPropertiesToFetch:[NSArray arrayWithObject:lastNameInitialProperty]];

确保获取请求只返回不同的结果(这是魔术的最后一个季度):
```
[fetchRequest setReturnsDistinctResults:YES];
```

通过此信函订购您的结果:

NSSortDescriptor * lastNameInitialSortOrder = [[[NSSortDescriptor alloc] initWithKey:@"lastNameInitial" ascending:YES] autorelease];

[fetchRequest setSortDescriptors:[NSArray arrayWithObject:lastNameInitialSortOrder]];

如果我理解这是如何工作的,那么我猜它将返回一个NSManagedObject数组,每个NSManagedObject只将lastNameInitial属性加载到内存中,它们是一组不同的姓氏首字母。

祝你好运,并报告这是如何工作的。我只是想知道这是否有效

fawsha1 13 年前

- (NSString *)stringGroupByFirstInitial {
    NSString *temp = [self uppercaseString];
    if (!temp.length || temp.length == 1)
        return self;
    return [temp substringToIndex:1];
}

Mike Baldus 15 年前

我经常遇到这个问题。我经常回到的最好的解决方案是给实体一个真正的初始属性。由于可以将字段设置为索引,因此作为实字段可以提供更高效的搜索和排序。在首次导入/创建数据时,拉出第一个首字母并用它填充第二个字段似乎并不需要太多工作。您必须以任何一种方式编写初始解析代码,但您可以为每个实体编写一次,以后不再编写。缺点似乎是每个实体存储一个额外字符(以及索引),实际上,这可能无关紧要。

再加一张。我避免修改生成的实体代码。也许我遗漏了一些东西,但是用于生成CoreData实体的工具不尊重我可能在其中输入的任何代码。生成代码时选择的任一选项都会删除我可能进行的任何自定义。如果我用聪明的小函数填充我的实体,那么我需要向那个实体添加一堆属性,我不能轻易地重新生成它。

Benny Davidovitz 9 年前

斯威夫特3

extension NSString{
    func firstChar() -> String{
        if self.length == 0{
            return ""
        }
        return self.substring(to: 1)
    }
}

然后使用firstChar键路径进行排序,在我的例子中是lastname.firstChar

request.sortDescriptors = [
            NSSortDescriptor(key: "lastname.firstChar", ascending: true),
            NSSortDescriptor(key: "lastname", ascending: true),
            NSSortDescriptor(key: "firstname", ascending: true)
        ]

最后对sectionNameKeyPath使用firstChar键路径

let controller = NSFetchedResultsController(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: "lastname.firstChar", cacheName: "your_cache_name")

-1

user698333 14 年前

我想我有更好的办法。将显示“视图中”而不是“瞬态”属性。重新计算NSManagedObject的派生属性并保存上下文。更改后,您可以重新加载表视图。

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView endUpdates];
    [self.tableView reloadData];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Capsid"];
    NSError *error = nil;
    NSArray *results = [self.managedObjectContext executeFetchRequest:request error:&error];
    if (error) {
        NSLog(@"refresh error");
        abort();
    }
    for (Capsid *capsid in results) {
        unsigned long long sum = 0;
        for (Touch *touch in capsid.vs) {
            sum += touch.count.unsignedLongLongValue;
        }
        for (Touch *touch in capsid.us) {
            sum += touch.count.unsignedLongLongValue;
        }
        capsid.sum = [NSNumber numberWithUnsignedLongLong:sum];
    }
    if (![self.managedObjectContext save:&error]) {
        NSLog(@"save error");
        abort();
    }
}

- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil) {
        return __fetchedResultsController;
    }

    // Set up the fetched results controller.
    // Create the fetch request for the entity.
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    // Edit the entity name as appropriate.
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Capsid" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    // Set the batch size to a suitable number.
    [fetchRequest setFetchBatchSize:20];

    // Edit the sort key as appropriate.
    //    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:NO];
//    NSSortDescriptor *sumSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"sum" ascending:NO];
//    NSArray *sortDescriptors = [NSArray arrayWithObjects:sumSortDescriptor, nil];
    [fetchRequest setReturnsDistinctResults:YES];
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"sum" ascending:NO];
    NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
    [fetchRequest setSortDescriptors:sortDescriptors];


    // Edit the section name key path and cache name if appropriate.
    // nil for section name key path means "no sections".
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return __fetchedResultsController;
}