小编sam*_*bol的帖子

在我的iOS应用程序中,我正在尝试更新数据库中的用户信息(使用Stackmob),但我不断收到"无法识别的选择器发送到实例".

- (IBAction)save:(UIButton *)sender {

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"User"];
NSPredicate *predicte = [NSPredicate predicateWithFormat:@"username == %@", self.username];
[fetchRequest setPredicate:predicte];

[self.managedObjectContext executeFetchRequest:fetchRequest onSuccess:^(NSArray *results) {

    NSManagedObject *todoObject = [results objectAtIndex:0];
    [todoObject setValue:@"example@gmail.com" forKey:@"email"];

    [self.managedObjectContext saveOnSuccess:^{
        NSLog(@"You updated the todo object!");
    } onFailure:^(NSError *error) {
        NSLog(@"There was an error! %@", error);
    }];

} onFailure:^(NSError *error) {

    NSLog(@"Error fetching: %@", error);

}];
}

这是我得到的完整错误:

-[NSNull length]: unrecognized selector sent to instance 0x1ec5678

2013-07-21 12:01:25.773 [29207:c07] *** Terminating app due to uncaught …