Question

有一个应用程序有一个人员列表和一个指令列表。当您在TextField中创建订单时，PickerView应显示一个员工列表（带名称）。我将按如下方式实施：

- (void)viewDidLoad {
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Employees"];
        self.empl=[[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
        UIPickerView *picker = [[UIPickerView alloc]init];
        picker.dataSource = self;
        picker.delegate = self;
        [picker setShowsSelectionIndicator:YES];
        [self.empTaskField setInputView:picker];
}



 #pragma mark - UIPickerView DataSource Method
    - (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{

    return 1;

}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{

        return self->_empl.count;

    }

    #pragma mark - UIPickerView Delegate Method

    -(NSString *) pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
        return [_empl objectAtIndex:row];
    }

单击TextField上显示的错误时：

27/03/2016 23：32：57.177员工任务[2730：150090] - [Employees copyWithZone：]：无法识别的选择器发送到实例 0x7fcf2ac84fd0 2016-03-27 23：32：57.513员工任务[2730： 150090] ***因未捕获的异常终止应用程序＆＃39; NSInvalidArgumentException＆＃39;，原因：＆＃39; - [Employees copyWithZone：]：无法识别的选择器发送到实例0x7fcf2ac84fd0＆＃39;

如何解决这个问题？

Answer 1

=＆GT;你应该作为字符串返回，所以你应该获取密钥的微粒索引行并返回它。如下面的代码

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{ NSArray
    Teacher *teacher = teacherForSubjectArray[row];
    NSString *teacherName = [NSString stringWithFormat:@"%@ %@ %@", teacher.firstName, teacher.middleName, teacher.lastName];
    return teacherName;
}

Answer 2

删除mutableCopy。 NSManagedObject不符合NSCopying协议。所以你的获取代码应该是

self.empl=[managedObjectContext executeFetchRequest:fetchRequest error:nil];

如何从PickerView中的Core Data获取数据？ iOS版

2 个答案: