當應用程序轉到後臺時網絡連接丟失

我正在使用CMIS(Content management interoperability services)從戶外服務器下載數據。我正在使用下面的代碼，它在一定程度上工作正常，但是當應用程序轉到後臺時，網絡連接會丟失，並且當應用程序到達前臺時，它會嘗試重試下載並且無法通知連接錯誤。由於我是新手，任何幫助將不勝感激。當應用程序轉到後臺時網絡連接丟失

- (void)testFileDownload 
{ 
    [self runTest:^ 
    { 
     [self.session retrieveObjectByPath:@"/ios-test" completionBlock:^(CMISObject *object, NSError *error) { 
      CMISFolder *testFolder = (CMISFolder *)object; 
      STAssertNil(error, @"Error while retrieving folder: %@", [error description]); 
      STAssertNotNil(testFolder, @"folder object should not be nil"); 

      CMISOperationContext *operationContext = [CMISOperationContext defaultOperationContext]; 
      operationContext.maxItemsPerPage = 100; 
      [testFolder retrieveChildrenWithOperationContext:operationContext completionBlock:^(CMISPagedResult *childrenResult, NSError *error) { 
       STAssertNil(error, @"Got error while retrieving children: %@", [error description]); 
       STAssertNotNil(childrenResult, @"childrenCollection should not be nil"); 

       NSArray *children = childrenResult.resultArray; 
       STAssertNotNil(children, @"children should not be nil"); 
       STAssertTrue([children count] >= 3, @"There should be at least 3 children"); 

       CMISDocument *randomDoc = nil; 
       for (CMISObject *object in children) 
       { 
        if ([object class] == [CMISDocument class]) 
        { 
         randomDoc = (CMISDocument *)object; 
        } 
       } 

       STAssertNotNil(randomDoc, @"Can only continue test if test folder contains at least one document"); 
       NSLog(@"Fetching content stream for document %@", randomDoc.name); 

       // Writing content of CMIS document to local file 
       NSString *filePath = [NSString stringWithFormat:@"%@/testfile", NSTemporaryDirectory()]; 
       //    NSString *filePath = @"testfile"; 
       [randomDoc downloadContentToFile:filePath 
            completionBlock:^(NSError *error) { 
             if (error == nil) { 
              // Assert File exists and check file length 
              STAssertTrue([[NSFileManager defaultManager] fileExistsAtPath:filePath], @"File does not exist"); 
              NSError *fileError = nil; 
              NSDictionary *fileAttributes = [[NSFileManager defaultManager] attributesOfItemAtPath:filePath error:&fileError]; 
              STAssertNil(fileError, @"Could not verify attributes of file %@: %@", filePath, [fileError description]); 
              STAssertTrue([fileAttributes fileSize] > 10, @"Expected a file of at least 10 bytes, but found one of %d bytes", [fileAttributes fileSize]); 

              // Nice boys clean up after themselves 
              [[NSFileManager defaultManager] removeItemAtPath:filePath error:&fileError]; 
              STAssertNil(fileError, @"Could not remove file %@: %@", filePath, [fileError description]); 
             } else { 
              STAssertNil(error, @"Error while writing content: %@", [error description]); 
             } 
             self.testCompleted = YES; 
            } progressBlock:nil]; 
      }]; 
     }]; 
    }]; 
}

當用戶按下home鍵時，連接失敗不會發生。它只有在磁蓋蓋關閉或超時時纔會失效。

來源

2013-05-15 Abilash

當應用程序移到後臺時，操作系統會讓應用程序5s完成暫停前的操作（保持RAM，但停止應用程序接收任何消息或執行任何操作）。如果您有一項任務需要在用戶按下主頁按鈕時運行完成，則可以使用後臺任務。從蘋果公司的文檔：

應用程序委託的applicationDidEnterBackground：方法有約5秒完成任何任務並返回。在實踐中，這個方法應該儘快返回。如果方法確實在時間耗盡之前沒有返回，則會終止您的應用並從內存中清除內存。如果您仍然需要更多時間來執行任務，請致電 beginBackgroundTaskWithExpirationHandler：方法請求後臺執行時間，然後在第線程中啓動任何長時間運行的任務。無論您是否啓動任何後臺任務， applicationDidEnterBackground：方法仍必須在5秒鐘內退出。

注意：UIApplicationDidEnterBackgroundNotification通知是也發送到讓您的應用程序的感興趣的部分知道它是輸入的背景。您的應用中的對象可以使用默認通知中心註冊此通知。

從http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html

來源

2013-05-15 18:34:52

使用可達代碼試試這個代碼，以節省下載一次數據：

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{ 
//try to access that local file for writing to it... 
NSFileHandle *hFile = [NSFileHandle fileHandleForWritingAtPath:self.localPath]; 
//did we succeed in opening the existing file? 
if (!hFile) 
{ //nope->create that file! 
    [[NSFileManager defaultManager] createFileAtPath:self.localPath contents:nil attributes:nil]; 
    //try to open it again... 
    hFile = [NSFileHandle fileHandleForWritingAtPath:self.localPath]; 
} 
//did we finally get an accessable file? 
if (!hFile) 
{ //nope->bomb out! 
    NSLog("could not write to file %@", self.localPath); 
    return; 
} 
//we never know - hence we better catch possible exceptions! 
@try 
{ 
    //seek to the end of the file 
    [hFile seekToEndOfFile]; 
    //finally write our data to it 
    [hFile writeData:data]; 
} 
@catch (NSException * e) 
{ 
    NSLog("exception when writing to file %@", self.localPath); 
    result = NO; 
} 
[hFile closeFile]; 
}

來源

2013-05-15 19:05:59

當應用程序轉到後臺時網絡連接丟失

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