iphone - 将 dispatch_async 与核心数据一起使用时获取 EXC_BAD_ACCESS

Question

我在 coredata 中有图像，我正在尝试为表格 View 延迟加载这些图像。每个单元使用相关核心数据实体的观察者在图像可用时更新图像。实体中的相关代码如下:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
  // The heavy lifting seems to be during firing of the fault and accessing data,
  // so i'm trying to do that in the background thread.
  UIImage *i = [UIImage imageWithData:self.imageEntity.data];
  // I now need to notify observers that the image is ready on the main thread
  dispatch_async(dispatch_get_main_queue(), ^{
    [self willChangeValueForKey:@"image"];
    image = i;
    [self didChangeValueForKey:@"image"];
  });
});

该项目使用 ARC，我没有收到任何编译器错误或警告，当我运行它时，它可以正常工作，直到我快速滚动，然后当我声明 i 时，我在线上收到 EXC_BAD_ACCESS。

我在这里错过了什么？

Answer 1

显然正在获取 CoreData objects is not thread safe .因此建议使用相同的 persistentStoreCoordinator，但使用不同的 ObjectContext。这是我更新后的代码，似乎不再崩溃:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
  @autoreleasepool {
    // Create a new context
    NSManagedObjectContext *backgroundContext = [[NSManagedObjectContext alloc] init];
    // Use an existing coordinator
    NSPersistentStoreCoordinator *coordinator = [[DataSource sharedDataSource] persistentStoreCoordinator];
    [backgroundContext setPersistentStoreCoordinator:coordinator];
    // Getting objectID does not fire the fault, so we grab it but actually fetch the object
    // on a background context to be thread safe.
    Image *imageEntity = (Image*)[backgroundContext objectWithID:self.imageEntity.objectID];
    image = [UIImage imageWithData:imageEntity.data];
    // Notify observers that the image is ready on the main thread
    dispatch_async(dispatch_get_main_queue(), ^{
      [self willChangeValueForKey:@"image"];
      [self didChangeValueForKey:@"image"];
    });
  }
});