如何从 PickerView 的 Core Data 中获取数据？ iOS

Question

有一个应用程序包含员工列表和说明列表。当您在 TextField 中创建订单时，PickerView 应该会出现一个员工列表（带有姓名）。我将实现如下：

- (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];
    }

当您单击文本字段时出现错误：

27/03/2016 23 : 32 : 57.177 Employee Task [ 2730 : 150090 ] - [Employees copyWithZone:]: unrecognized selector sent to instance 0x7fcf2ac84fd0 2016-03-27 23 : 32 : 57.513 Employee Task [ 2730 : 150090 ] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '- [Employees copyWithZone:]: unrecognized selector sent to instance 0x7fcf2ac84fd0'

如何解决这个问题？

Answer 1

=> 你应该 return 作为字符串，所以你应该获取键的特定索引行和 return 它..就像下面的代码

-(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 的 Core Data 中获取数据？ iOS

How to get the data from the Core Data in PickerView? iOS

iphone

core-data

objective-c

uipickerview

ios