iphone - 如何使用 NSFetchedResultsController 和 UISearchDisplayController

Question

我一直在使用 Core Data 创建 iPhone 应用程序。

首先，一起使用 NSFetchedResultsController 和 UISearchDisplayController 来获取结果是否有意义？您还能推荐其他东西吗？

我一直在尝试将 NSFetchedResultController 和 UISearchDisplayController 结合起来。我一直在考虑在 UIViewController 的 NSFetchedResultController 的 (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption 方法中设置 NSPredicate。但这效果不太好。

那么，您知道如何为我的问题实现解决方案吗？感谢您发布答案或优秀教程的链接。

编辑

这是我的代码。 UISearchDisplayDelegate 方法调用方法 (void)filterContentForSearchText:(NSString*)searchText range:(NSString*)scope ，该方法应在 NSFetchedResultController 中设置谓词。我还添加了 NSFetchedResultController 的代码。

- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString
{
    [self filterContentForSearchText:searchString scope:
     [[self.searchDisplayController.searchBar scopeButtonTitles] objectAtIndex:[self.searchDisplayController.searchBar selectedScopeButtonIndex]]];

    // Return YES to cause the search result table view to be reloaded.
    return YES;
}


- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption
{
    [self filterContentForSearchText:[self.searchDisplayController.searchBar text] scope:
     [[self.searchDisplayController.searchBar scopeButtonTitles] objectAtIndex:searchOption]];

    // Return YES to cause the search result table view to be reloaded.
    return YES;
}


- (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope
{
    NSString *query = self.searchDisplayController.searchBar.text;
    if (query && query.length) {
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"Name contains[cd] %@", query];
        [fetchedResultsController.fetchRequest setPredicate:predicate];
    }

    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {
        // Handle error
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        exit(-1);  // Fail
    }  

}


- (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:@"Event" inManagedObjectContext: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];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, 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:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptor release];
    [sortDescriptors release];

    return fetchedResultsController;
} 

Answer 1

看看你的代码，它就在那里。我在使用这种方法更改搜索时遇到了问题。解决方法:清除缓存!

假设您按如下方式启动了获取结果 Controller 。请注意cacheName 属性。

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

当您更改谓词时，只需添加:

 [NSFetchedResultsController deleteCacheWithName:@"UserSearch"];

就像魔术一样，它会很好地发挥作用。

您还需要监视搜索显示 Controller 何时结束其搜索，并删除您的谓词。

虽然这个线程看起来已经死了，但我在谷歌上找到了它，所以也许有人会利用这个。 :)