NSFetchedResultsController用于UITableView的多个实体

2 回答

• -2

  可悲的是，我只知道这个问题的UGLY解决方案 .

  在 User .m文件中实现 setProfilePicture: ，如下所示：

  //NOT TESTED IN A MULTITHREADED ENV
  - (void) setProfilePicture:(NSData *)data
  {
      [self willChangeValueForKey:@"profilePicture"];
      [self setPrimitiveValue:data forKey:@"profilePicture"];
      [self.posts enumerateObjectsUsingBlock:^(Post* p, BOOL *stop) {
          [p willChangeValueForKey:@"user"];
          [p didChangeValueForKey:@"user"];
      }];
      [self didChangeValueForKey:@"profilePicture"];
  }
  

  这将通知FRC Post元素有更改 .

  您可能会找到更多信息here

  Edit:

  要获取访问数据，您可以将其添加到 User .m：

  //UNTESTED
  + (void) mergeToMain:(NSNotification*)notification
  {
      AppDelegate* appDel = (AppDelegate*)[[UIApplication sharedApplication] delegate];
      [appDel.managedObjectContext performSelectorOnMainThread:@selector(mergeChangesFromContextDidSaveNotification:) 
                                                    withObject:notification 
                                                 waitUntilDone:YES];
  }
  
  - (NSData*)_profilePicture
  {
      return [self primitiveValueForKey:@"profilePicture"];
  }
  
  - (NSData*) profilePicture
  {
      [self willAccessValueForKey:@"profilePicture"];
      NSData* picData = [self primitiveValueForKey:@"profilePicture"];
      if (!name) {
          __block NSManagedObjectID* objectID = self.objectID;
          //This solves the multiple downloads per item by using a single queue
          //for all profile pictures download.
          //There are more concurrent ways to accomplish that
          dispatch_async(downloadSerialQueue, ^{ //define some serial queue for assuring you down download multiple times the same object
              NSError* error = nil;
              AppDelegate* appDel = (AppDelegate*)[[UIApplication sharedApplication] delegate];
              NSManagedObjectContext* context = [[NSManagedObjectContext alloc] init];
              [context setPersistentStoreCoordinator:appDel.persistentStoreCoordinator];
              [context setUndoManager:nil];
              User* user = (User*)[context existingObjectWithID:objectID error:&error];
              if (user && [user _profilePicture] == nil) {
                  NSData *data = //[method to retrieve data from server];
                  if (data) {
                      if (user) {
                          user.profilePicture = data;
                      } else {
                          NSLog(@"ERROR:: error fetching user: %@",error);
                          return;
                      }
                      [[NSNotificationCenter defaultCenter] addObserver:[self class] selector:@selector(mergeToMain:) name:NSManagedObjectContextDidSaveNotification object:context];
                      [context save:&error];
                      [[NSNotificationCenter defaultCenter] removeObserver:[self class] name:NSManagedObjectContextDidSaveNotification object:context];
                  }                    
              }
          });
      }
      [self didAccessValueForKey:@"profilePicture"];
      return picData;
  }
  

  回复于 2024-04-25T17:12:07+08:00
• 4

  我认为这个问题可以在没有涉及NSFetchedResultsController的情况下解决 .

  • 使用SDWebImage，SDWebImage可以异步加载来自远程服务器的图像，只需执行以下操作：

  [myImageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                 placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
  

  • 使用KVO，向User实体添加观察者并相应地更新相应的图像视图 . 但是KVO的代码相当复杂，ReactiveCocoa可以简化它们：

  [RACAble(user.profilePicture) subscribeNext:^(UIImage *image) {
      [myImageView setImage:image];
  }];
  

  回复于 2024-04-25T17:12:07+08:00