Question

我创建了一个对象，其中包含最终将管理核心数据中的数据的属性。

我想在此对象中创建方法来设置将保存到核心数据中的数据，以及从核心数据获取所有数据并在对象中设置属性的方法，这样我就可以将所有内容包含在一个对象中。 / p>

我用来设置对象属性的对象没有正确设置它。它将它们设置在方法的一部分内，但在方法的另一部分中，在方法之外，属性为null。

这是一个范围问题，我显然没有理解，所以我转向专家。请告知我误入歧途的地方。再次感谢您的帮助！编

对象定义： .m文件

 @implementation GenObject

 @synthesize name = _name;
 @synthesize address = _address;

 - (void)getGenData
 {
      MyAppDelegate *genDataAppDelegate = [[UIApplication sharedApplication] delegate]; // Create a variable to the app delegate
      NSManagedObjectContext *genDataContext = [genDataAppDelegate managedObjectContext]; // Create a context

      NSEntityDescription *getDataEntityDesc = [NSEntityDescription entityForName:@"GeneralData" inManagedObjectContext:genDataContext];  // Create a description for the core data
      NSFetchRequest *genDataRequest = [[NSFetchRequest alloc] init]; // Create a Fetch request for the core data

      [genDataRequest setEntity:getDataEntityDesc]; // Set the fetch requests entity description

      NSManagedObject *genDataMatches = nil; // Create a managed object
      NSError *genDataCoreError; // Create an error object

      NSArray *genDataCoreObjectsArray = [genDataContext executeFetchRequest:genDataRequest error:&genDataCoreError]; // Fetch the core data and load the objects array
      int genDataCoreObjectsCount = [genDataCoreObjectsArray count]; // Get the count of the objects fetched

      if ([genDataCoreObjectsArray count] == 0) // Check to see if there were any objects fetched
      {
          //NSLog(@"No matches");
      } 
      else // If there were objects fetched then loop over them
     {
         for(int y = 0; y < genDataCoreObjectsCount; y++) // Loop over the objects fetched
         {
             genDataMatches = [genDataCoreObjectsArray objectAtIndex:y]; // Get the current object
             self.name = [[genDataMatches valueForKey:@"name"] retain];
             self.address = [[genDataMatches valueForKey:@"address"] retain];
             NSLog(@"BASE URL %@",self.baseurl); // WORKS HERE!!!
        }   
    }
    NSLog(@"BASE URL %@",self.baseurl); // DOES NOT WORK HERE!!!
 }
 @end

.h文件

 @interface GenObject : NSObject
 {
     NSString    *_name;    
     NSString    *_address;   
 }

 @property (nonatomic, retain) NSString  *name;
 @property (nonatomic, retain) NSString  *address;

 - (void)setGenIntitalData;
 @end

如果我尝试从一个不同的类中调用它，就像说ViewController一样...... 注意：在viewController中，genDataObj是viewController的属性

 - (void)viewDidLoad
 {
     self.genDataObj = [GenData new];
     [self.genDataObj setGenIntitalData]; // Setup the gendata core data
     [self.genDataObj getGenData]; // Set up the gen data from the core data

     NSLog(@"NAME: %@", self.genDataObj.name); // NAME IS nil HERE!!!!

     [super viewDidLoad];
 }

Answer 1

您应该确认您的NSManagedObject实际上是在返回数据。试试这个：

 - (void)getGenData
 {
    MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = [appDelegate managedObjectContext]; 
    NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"GeneralData"];

    NSManagedObject *genData = nil;
    NSError *fetchError = nil;
    NSArray *genDataObjects = [context executeFetchRequest:request error:&fetchError];
    [request release];
    if( fetchError )
        NSLog(@"%s - ERROR fetching genData: %@,%@",__FUNCTION__,fetchError,[fetchError userInfo]);
    else
    {
        if( [genDataObjects count] == 0 )
            NSLog(@"%s - No matches for genData",__FUNCTION__);
        else
        {
            genData = [genDataObjects objectAtIndex:0];
            NSLog(@"%s - genData.name = %@",__FUNCTION__,[genData valueForKey:@"name"]);
            self.name = [genData valueForKey:@"name"];
            self.address = [genData valueForKey:@"address"];
        }
    }
}

在setGenIntitalData中，您是否将更改保存到持久性存储中？我假设在setGenIntitalData你正在创建初始设置;但如果未保存NSManagedObject，则后续提取将产生无效数据。

如何在对象中保留属性集

1 个答案: