当应用程序转到后台时网络连接丢失

我正在使用CMIS(Content management interoperability services)从户外服务器下载数据。我正在使用下面的代码，它在一定程度上工作正常，但是当应用程序转到后台时，网络连接会丢失，并且当应用程序到达前台时，它会尝试重试下载并且无法通知连接错误。由于我是新手，任何帮助将不胜感激。当应用程序转到后台时网络连接丢失

- (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]; 
      }]; 
     }]; 
    }]; 
}

当用户按下home键时，连接失败不会发生。它只有在磁盖盖关闭或超时时才会失效。

来源

2013-05-15 Abilash

当应用程序移到后台时，操作系统会让应用程序5s完成暂停前的操作（保持RAM，但停止应用程序接收任何消息或执行任何操作）。如果您有一项任务需要在用户按下主页按钮时运行完成，则可以使用后台任务。从苹果公司的文档：

应用程序委托的applicationDidEnterBackground：方法有约5秒完成任何任务并返回。在实践中，这个方法应该尽快返回。如果方法确实在时间耗尽之前没有返回，则会终止您的应用并从内存中清除内存。如果您仍然需要更多时间来执行任务，请致电 beginBackgroundTaskWithExpirationHandler：方法请求后台执行时间，然后在第线程中启动任何长时间运行的任务。无论您是否启动任何后台任务， applicationDidEnterBackground：方法仍必须在5秒钟内退出。

注意：UIApplicationDidEnterBackgroundNotification通知是也发送到让您的应用程序的感兴趣的部分知道它是输入的背景。您的应用中的对象可以使用默认通知中心注册此通知。

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

来源

2013-05-15 18:34:52

使用可达代码试试这个代码，以节省下载一次数据：

-(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]; 
}

来源

2013-05-15 19:05:59

当应用程序转到后台时网络连接丢失

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