使用没有搜索栏的获取结果控制器过滤表视图？

Question

我有一个 UITableView 使用 NSFetchedResults 控制器来填充表格，如下所示：

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

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

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Expense" inManagedObjectContext:self.managedObjectContext];

    [fetchRequest setEntity:entity];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"expenseDate" ascending:NO];

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

    [fetchRequest setFetchBatchSize:20];

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

    self.fetchedResultsController = theFetchedResultsController;

    self.fetchedResultsController.delegate = self;

    return _fetchedResultsController;

}

我希望能够过滤结果，但出于几个不同的原因，我不想使用搜索栏和搜索显示控制器。

无论如何我可以使用自己的谓词过滤结果然后重新加载表吗？

Answer 1

获取结果后，您将通过UITableView 填充一个新的数据数组，然后您可以调用：

[tableView reloadData];

Answer 2

当然，您可以将 NSPredicate 添加到您的 NSFetchRequest 中，然后使用您的 NSFetchedResultsController 执行新的提取。

这是我做过类似事情的一个例子：

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Expense" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];
    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"expenseDate" ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    [fetchRequest setFetchBatchSize:20];

    //Apply your filtering predicate to the fetchRequest if necessary
    NSPredicate *filterPrediate = [self getFilterPredicate];
    if(filterPrediate){
    [fetchRequest setPredicate:filterPrediate];
    }

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

    _fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;
    return _fetchedResultsController;

}

- (NSPredicate *)getFilterPredicate
{
    //Get or create your filtering predicate here.
    //You can combine NSPredicates using a NSCompoundPredicate if necessary.
    if(shouldFilter){
        return yourNSPrecicate;
    }else{
        return nil;
    }
}

- (void)reloadFetchedViewController
{
    NSError *error;
    if (![self.fetchedResultsController performFetch:&error]) {
        // Update to handle the error appropriately.
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    }
}

然后用新的查询更新 UITableView：

self.fetchedResultsController = nil;
[self reloadFetchedViewController];
[self.tableView reloadData];