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我在（核心數據）實體中保存了我的tableviewdata的最新互聯網請求，但在關於「錯誤」的錯誤例外方面存在問題。 我有兩個方法'loadData'獲取最新的'ordersitems'將被加載在我的tableview和'loadThumbnails'，它會嘗試緩存縮略圖到核心數據實體。 當managedobject被刪除並且縮略圖方法仍嘗試訪問它時，會發生此問題。雖然我做了一個變量stopThumbnails來停止loadThumbnails方法，但問題仍在繼續。在IOS6中使用核心數據（刪除/編輯）
什麼是適當的iOS 6方式來延遲加載圖像並將它們保存到coredata，但檢查對象是否沒有被刪除？我發現這Core Data multi thread application這是有用的，但我對核心數據的新手理解仍然有限，我有問題編寫代碼。我讀了關於http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/coredata/Articles/cdConcurrency.html的蘋果文檔，但很難完全理解。
我想至少我的http請求加載臺異步（但最好儘可能地）我想出了以下內容：
-(void)viewdidload
{
NSFetchRequest *fetchReq = [NSFetchRequest fetchRequestWithEntityName:@"OrderItems"];
fetchReq.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES]];
self.data = [self.managedObjectContext executeFetchRequest:fetchReq error:nil];
MYFILTER = @"filter=companyX";
[self loadData];
}
-(void)loadData
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//json request from url
NSDictionary *reqData = myOrderJSONRequest(MYFILTER);
dispatch_async(dispatch_get_main_queue(), ^{
if(reqData!=NULL && reqData!=nil)
{
//request successful so delete all items from entity before inserting new ones
stopThumbnails = YES;
for(int i=self.data.count-1;i>=0;i--)
{
[self.managedObjectContext deleteObject:[self.data objectAtIndex:i]];
}
[self.managedObjectContext save:nil];
if(reqData.count>0)
{
//insert latest updates
for (NSDictionary *row in reqData){
OrderItem *item = [NSEntityDescription insertNewObjectForEntityForName:@"OrderItem" inManagedObjectContext:self.managedObjectContext];
item.order_id = [NSNumber numberWithInt:[[row objectForKey:@"order_id"] intValue]];
item.description = [row objectForKey:@"description"];
item.thumbnail_url = [row objectForKey:@"thumbnail_url"];
}
[self.managedObjectContext save:nil];
}
NSFetchRequest *fetchReq = [NSFetchRequest fetchRequestWithEntityName:@"OrderItems"];
fetchReq.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES]];
self.data = [self.managedObjectContext executeFetchRequest:fetchReq error:nil];
[TableView reloadData];
//LOAD THUMBNAILS ASYNCHRONOUS
stopThumbnails = NO;
[self loadThumbnails];
}
else{
//NO INTERNET
}
});
});
}
-(void)loadThumbnails
{
if(!loadingThumbnails)
{
loadingThumbnails = YES;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
for (int i=0;i<self.data.count; i++) {
if(!stopThumbnails)
{
OrderItem *item = [self.data objectAtIndex:i];
if(item.thumbnail==NULL)
{
//ASYNCHRONOUS IMAGE REQUEST
NSURL *image_url = [NSURL URLWithString:item.thumbnail_url];
NSData *image_data = [NSData dataWithContentsOfURL:image_url];
dispatch_async(dispatch_get_main_queue(), ^{
if(image_data!=nil && image_data!=NULL && !stopThumbnails)
{
//IMAGE REQUEST SUCCESSFUL
item.thumbnail = image_data;
[self.managedObjectContext save:nil];
//RELOAD AFFECTED TABLEVIEWCELL
NSIndexPath* rowToReload = [NSIndexPath indexPathForRow:i inSection:0];
NSArray* rowsToReload = [NSArray arrayWithObjects:rowToReload, nil];
[TableView reloadRowsAtIndexPaths:rowsToReload withRowAnimation:UITableViewRowAnimationFade];
}
else
{
loadingThumbnails = NO;
return;
}
});
}
if(stopThumbnails)
{
dispatch_async(dispatch_get_main_queue(), ^{
loadingThumbnails = NO;
return;
});
}
}
else{
dispatch_async(dispatch_get_main_queue(), ^{
loadingThumbnails = NO;
return;
});
}
}
dispatch_async(dispatch_get_main_queue(), ^{
loadingThumbnails = NO;
return;
});
});
}
}
任何幫助當然是極大的讚賞:)