ios - 为什么 nspredicate 不起作用

Question

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

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"KeyRefEntity" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    [fetchRequest setFetchBatchSize:20];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"time" ascending:NO];
    NSArray *sortDescriptors = @[sortDescriptor];

    [fetchRequest setSortDescriptors:sortDescriptors];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"time" cacheName:@"Master"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _fetchedResultsController;
}

---

- (void) searchBarSearchButtonClicked:(UISearchBar *)theSearchBar {
    if (self.searchBar.text !=nil)
    {
        NSPredicate *predicate =[NSPredicate predicateWithFormat:@"ref CONTAINS[cd] %@", self.searchBar.text];
        [self.fetchedResultsController.fetchRequest setPredicate:predicate];
    }
    else
    {
        NSPredicate *predicate =[NSPredicate predicateWithFormat:@"All"];
        [self.fetchedResultsController.fetchRequest setPredicate:predicate];
    }

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

    [self.searchBar resignFirstResponder];

    [self.tableView reloadData];
}

我正在尝试使用此代码进行搜索，但 searchBarSearchButtonClicked: 内的代码不起作用我放置了一个断点，所有代码都执行但没有任何反应。

Answer 1

不确定 [NSPredicate predicateWithFormat:@"All"]; 应该做什么，但它不太可能起作用。当您的搜索文本更改时，您应该替换提取请求并将新的提取请求添加到 FRC。来自 FRC 文档:

initWithFetchRequest:managedObjectContext:sectionNameKeyPath:cacheName:

Important: You must not modify fetchRequest after invoking this method. For example, you must not change its predicate or the sort orderings.

您的另一个问题是 FRC 正在使用缓存。不支持在使​​用缓存时更改获取请求。一般建议是不使用缓存。如果由于某种原因必须使用缓存，那么当您更改获取请求时(之前)，您还需要删除旧缓存-deleteCacheWithName:)。

请参阅 FRC 文档 here .