NSFetchRequest 返回值

Posted 2023-03-04

【中文标题】NSFetchRequest 返回值

【英文标题】：NSFetchRequest return value

【发布时间】：2012-03-01 11:59:31

【问题描述】：

我不明白为什么这段代码会返回错误

- (void) deleteCategoriesWithNoProducts
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Category" inManagedObjectContext:self.itemDatabase.managedObjectContext];
    [request setEntity:entity]; 

    //NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Category"];


    NSSortDescriptor *sortDescriptor = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)]];    

    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [request setSortDescriptors:sortDescriptors];

    NSError *error;
    NSArray *fetchResults = [self.itemDatabase.managedObjectContext executeFetchRequest:request error:&error];

这是错误：

-[__NSArrayI key]: unrecognized selector sent to instance 0x8267ad0
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI key]: unrecognized selector sent to instance 0x8267ad0'

希望有人可以帮助我。谢谢！

【参考方案1】：

这是你的错误：

NSSortDescriptor *sortDescriptor = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)]];    

应该是：

NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)];    

那行也应该在编译器中给你一个警告。

【讨论】：

别忘了在方法结束时释放资源。

哦，原来如此，有点棘手啊。感谢@yuji 指出这一点。