我正在制作一个从服务器获取产品列表的应用程序。然后我将它们存储在核心数据数据库中,并使用GMGridView呈现它们,数据源是 NSFetchedResultsController。当我更改服务器中的产品详细信息时,我希望我的 iOS 应用程序能够同步并进行必要的更改,因此我实现了 NSFetchedResultsControllerDelegate 方法。我应该如何正确更新我的 gridView?
- (void)controller:(NSFetchedResultsController *)controller
didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath
forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
switch(type)
{
case NSFetchedResultsChangeInsert:
[_currentData insertObject:anObject atIndex:newIndexPath.row];
[_currentData removeObjectAtIndex:indexPath.row];
[_gmGridView insertObjectAtIndex:newIndexPath.row animated:YES];
[_gmGridView removeObjectAtIndex:indexPath.row animated:YES];
[_gmGridView reloadObjectAtIndex:newIndexPath.row animated:YES];
[_gmGridView reloadObjectAtIndex:indexPath.row animated:YES];
[_gmGridView reloadData];
//[self updatePageControl];
break;
case NSFetchedResultsChangeDelete:
[_currentData removeObjectAtIndex:indexPath.row];
[_gmGridView removeObjectAtIndex:indexPath.row animated:YES];
//[self updatePageControl];
[_gmGridView reloadInputViews];
[_gmGridView reloadData];
break;
case NSFetchedResultsChangeUpdate:
[_gmGridView reloadObjectAtIndex:indexPath.row animated:YES];
////////might be irrelevant, but just trying it out
[_currentData insertObject:anObject atIndex:newIndexPath.row];
[_currentData removeObjectAtIndex:indexPath.row];
[_gmGridView insertObjectAtIndex:newIndexPath.row animated:YES];
[_gmGridView removeObjectAtIndex:indexPath.row animated:YES];
[_gmGridView reloadObjectAtIndex:newIndexPath.row animated:YES];
[_gmGridView reloadObjectAtIndex:indexPath.row animated:YES];
////////
[_gmGridView reloadInputViews];
[_gmGridView reloadData];
break;
case NSFetchedResultsChangeMove:
[_currentData removeObjectAtIndex:indexPath.row];
[_currentData insertObject:anObject atIndex:newIndexPath.row];
[_gmGridView removeObjectAtIndex:indexPath.row animated:YES];
[_gmGridView insertObjectAtIndex:newIndexPath.row animated:YES];
[_gmGridView reloadInputViews];
[_gmGridView reloadData];
break;
}
}
一些细节:
_currentData = [[self.fetchedResultsController fetchedObjects]mutableCopy];
//I did this because previously I wasn't using a fetchedResultsController but a NSMutableArray instead. I know that it's inefficient (because I have 2 models) but this is the simplest implementation I want to do now.
我通过从相同的本地 URL 修改相同的 UIManagedDocument alloc,init-ed 在不同的类中更改 CoreData。
但是,我遇到了两个重要问题:
- 数据库中的项目已更新(例如更改产品名称或价格)但更改未反映在 UI 中,即我无法正确重新加载我的 GMGridViewCell。(注意上面与重新加载相关的代码)
- 大多数时候,我在服务器中更新的产品在数据库中是重复的,尽管我有一个机制来防止这样的错误。(在创建产品之前,我首先使用唯一标识符搜索现有产品。如果有现有产品,我只需修改其详细信息)。这是代码:
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Product"];
request.predicate = [NSPredicate predicateWithFormat:@"product_id = %@", [imonggoInfo objectForKey:PRODUCT_ID]];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
request.sortDescriptors = [NSArray
arrayWithObject:sortDescriptor]; NSError *error = nil;
NSArray *matches = [context executeFetchRequest:request error:&error];
if (!matches | ([matches count] > 1)){
//handle error
}else if ([matches count] == 0){
//make a new product
}else{
//return existing
item = [matches lastObject];
}