未调用NSSortDescriptor [英] NSSortDescriptor not being called

问题描述

我正在尝试对实体文件夹执行获取请求，我想要一个名为 xyz 的文件夹作为排序时的最后一个对象。

I'm trying to execute a fetch request on an entity Folders, and I want a folder named xyz to be the last object when sorted.

  NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription 
                                   entityForName:@"Folder" inManagedObjectContext:appDelegate.managedObjectContext];

    [fetchRequest setEntity:entity];

    NSSortDescriptor *lastDescriptor =
    [[[NSSortDescriptor alloc] initWithKey:@"folderName" ascending:YES comparator:^NSComparisonResult(NSString* name1, NSString* name2) {
        NSLog(@"descriptor");
        if ([name1 isEqualToString:@"xyz"]) {
            return NSOrderedAscending;
        }
        if ([name2 isEqualToString:@"xyz"]) {
            return NSOrderedDescending;
        }

        return [name1 compare:name2];
    }] autorelease];  


    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:lastDescriptor]];
    [fetchRequest setFetchBatchSize:5];

    NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:appDelegate.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
    self.fetchedResultsController = theFetchedResultsController;
    self.fetchedResultsController.delegate=self;   

    [fetchRequest release];
    [theFetchedResultsController release];

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

但是没有一个NSLog语句被调用。他们应该吗？并且文件夹xyz不会最后出现，但是一切都按字母顺序排序。我做错了什么？

But none of the NSLog statements are being called. Are they supposed to? And the folder xyz does not appear last, but everything ends up being sorted in alphabetical order. Am I doing something wrong?

编辑：完整代码

推荐答案

此代码（您的代码）的工作原理：

This code (your code) works:

- (void)sortMe {

    NSDictionary *d0 = [NSDictionary dictionaryWithObject:@"efg" forKey:@"folderName"];
    NSDictionary *d1 = [NSDictionary dictionaryWithObject:@"xyz" forKey:@"folderName"];
    NSDictionary *d2 = [NSDictionary dictionaryWithObject:@"abc" forKey:@"folderName"];
    NSDictionary *d3 = [NSDictionary dictionaryWithObject:@"def" forKey:@"folderName"];
    NSArray *testMe = [NSArray arrayWithObjects:d0, d1, d2, d3, nil];

    NSSortDescriptor *lastDescriptor =
    [[NSSortDescriptor alloc] initWithKey:@"folderName" ascending:YES comparator:^NSComparisonResult(NSString* name1, NSString* name2) {
        NSLog(@"descriptor");
        if ([name1 isEqualToString:@"xyz"]) {
            return NSOrderedAscending;
        }
        if ([name2 isEqualToString:@"xyz"]) {
            return NSOrderedDescending;
        }

        return [name1 compare:name2];
    }];

    NSArray *sorted = [testMe sortedArrayUsingDescriptors:[NSArray arrayWithObject:lastDescriptor]];
    for (NSDictionary *d in sorted) {
        NSLog(@"value=%@", [d valueForKey:@"folderName"]);
    }
}

我预测这个代码也可以工作：

I predict this code will work, too:

NSError *error;
NSArray *result =  [appDelegate.managedObjectContext executeFetchRequest:fetchRequest error:&error];
// log the array

我认为问题出在NSFetchedResultsController委托设置，在代码中。

I think the problem is in the NSFetchedResultsController delegate setup, elsewhere in the code.

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