问题描述
我目前有一个选项，允许用户更改我的iPhone应用程序中类别的显示顺序。
我想使用NSFetchedResultsController因此段标题是由category.displayOrder排序的category.name，其中category与我正在读取的实体具有TO-ONE关系。我可以使切片正常工作的唯一方法是使用category.displayOrder作为节标题。
NSSortDescriptor * sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey：@category.displayOrderascending：YES];
NSSortDescriptor * sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey：@nameascending：YES];
NSArray * sortDescriptors = [[NSArray alloc] initWithObjects：sortDescriptor1，sortDescriptor2，nil]
[fetchRequest setSortDescriptors：sortDescriptors];
[fetchRequest setFetchBatchSize：10];
NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest
managedObjectContext：managedObjectContext
sectionNameKeyPath：@category.name
cacheName：nil];
关于如何命名段标题与我排序的属性不同的任何想法？ / p>
不知道我是否完全理解你的问题，但我在我的应用程序中做类似的事情，这里是如何让它工作：
首先，fetchedResultsController方法，其中我根据我想做什么设置排序描述和谓词。在这种情况下，我想按发布日期THEN按名称排序电影标题。
在我的fetchresultscontroller定义中，将sectionNameKeyPath设置为releaseDate因此我的部分标题将基于日期。
- （NSFetchedResultsController *）fetchedResultsController {
if（fetchedResultsController_！= nil）{
return fetchedResultsController_;
}
NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init];
NSSortDescriptor * sortByReleaseDate = [[NSSortDescriptor alloc] initWithKey：@releaseDateascending：NO];
NSSortDescriptor * sortByName = [[NSSortDescriptor alloc] initWithKey：@titleascending：YES];
NSArray * sortDescriptors = [[NSArray alloc] initWithObjects：sortByReleaseDate，sortByName，nil];
[fetchRequest setSortDescriptors：sortDescriptors];
[sortDescriptors release];
[sortByName release];
[sortByReleaseDate release];
NSPredicate * predicate = [NSPredicate predicateWithFormat：@（type =='Movies'）AND（releaseDate< =％@）AND（releaseDate> =％@），[NSDate date]，[NSDate dateWithTimeIntervalSinceNow ：kOneDayTimeInterval * -30]];
[fetchRequest setPredicate：predicate];
NSEntityDescription * entity = [NSEntityDescription entityForName：@MovieinManagedObjectContext：self.managedObjectContext];
[fetchRequest setEntity：entity];
NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest managedObjectContext：self.managedObjectContext sectionNameKeyPath：@releaseDatecacheName：nil];
... //在这里执行并返回fetch，错误处理等...
return fetchedResultsController_;
}
然后在我的表视图数据源委托方法中，我返回在将我的NSDate转换为NSString之后，每个头的实际标题（记住你必须返回NSString为一个tableview头标题。
（NSString *）tableView：（UITableView *）tableView titleForHeaderInSection：（NSInteger）section {
NSString * rawDateStr = [[[self.fetchedResultsController sections] objectAtIndex：section] name];
/ / convert default date string to NSDate ...
NSDateFormatter * formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setDateFormat：@yyyy-MM-dd HH：mm：ss ZZ ];
NSDate * date = [formatter dateFromString：rawDateStr];
//将NSDate转换为我们想要的格式...
[formatter setDateFormat：@d MMMM yyyy ];
NSString * formattedDateStr = [formatter stringFromDate：date];
return formattedDateStr;
}
因此，如果我想改变我的数据显示方式，例如通过titleName来组织，我会将我的fetchedResultsController对象更改为：
NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest managedObjectContext：self.managedObjectContext sectionNameKeyPath：@titleNamecacheName：nil];
并修改我的tableview：titleForHeaderInSection：数据源方法只是返回titleName ）：
- （NSString *）tableView：（UITableView *）tableView titleForHeaderInSection：（NSInteger）section {
return [[[self.fetchedResultsController sections] objectAtIndex：section] name];
}
我希望这可以帮助您找到解决您的具体问题的解决方案。 >
干杯，
Rog
I currently have an option that allows a user to change the display order of a category in my iPhone app.
I want to section the table view using a NSFetchedResultsController so that the section titles are the "category.name" ordered by "category.displayOrder" where "category" has a TO-ONE relationship with the entity I am fetching. The only way I can get the sectioning to work correctly is by using "category.displayOrder" as the section title.
NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"category.displayOrder" ascending:YES];
NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1, sortDescriptor2, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
[fetchRequest setFetchBatchSize:10];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:managedObjectContext
sectionNameKeyPath:@"category.name"
cacheName:nil];
Any ideas on how I can name the section title something different then the property I am sorting with?
Not sure if I understand your question completely, but I do something similar in my app and here's how I get it to work:
Firstly, the fetchedResultsController method, where I set the sort descriptions and predicates based on what I am trying to do. In this case I want to sort movie titles by release date THEN by name. Then with my predicate I grab entities of a specific 'type' and within a certain 'releaseDate' range.
In my fetchresultscontroller definition, you set the sectionNameKeyPath to "releaseDate" so my section headers will be based on a date.
- (NSFetchedResultsController *)fetchedResultsController {
if (fetchedResultsController_ != nil) {
return fetchedResultsController_;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSSortDescriptor *sortByReleaseDate = [[NSSortDescriptor alloc] initWithKey:@"releaseDate" ascending:NO];
NSSortDescriptor *sortByName = [[NSSortDescriptor alloc] initWithKey:@"title" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortByReleaseDate,sortByName, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
[sortDescriptors release];
[sortByName release];
[sortByReleaseDate release];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(type == 'Movies') AND (releaseDate <= %@) AND (releaseDate >= %@)", [NSDate date], [NSDate dateWithTimeIntervalSinceNow:kOneDayTimeInterval*-30]];
[fetchRequest setPredicate:predicate];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Movie" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"releaseDate" cacheName:nil];
...// Perform and return fetch here, error handling etc...
return fetchedResultsController_;
}
Then in my table view data source delegate methods, I return the actual title for each header after transforming my NSDate into NSString (remember you have to return NSString for a tableview header title.
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
NSString *rawDateStr = [[[self.fetchedResultsController sections] objectAtIndex:section] name];
//convert default date string to NSDate...
NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss ZZ"];
NSDate *date = [formatter dateFromString:rawDateStr];
//convert NSDate to format we want...
[formatter setDateFormat:@"d MMMM yyyy"];
NSString *formattedDateStr = [formatter stringFromDate:date];
return formattedDateStr;
}
So if I wanted to change the way my data is being displayed to be organised by titleName for instance, I'd change my fetchedResultsController object to:
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"titleName" cacheName:nil];
And modify my tableview:titleForHeaderInSection: data source method to simply return the titleName (which is already a string):
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
return [[[self.fetchedResultsController sections] objectAtIndex:section] name];
}
I hope this helps you find a solution to your specific problem.
Cheers,Rog
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