Network connection is losing when the app goes to the background - iphone

Question

I am using CMIS(Content management interoperability services) to download data from the alfresco server. I am using the following code and it works fine to some extent but when the application goes to background, the network connection is lost and when the app comes to foreground, it tries to retry the download and fails saying connection error. As I am a newbie any help will be much appreciated.
- (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];
}];
}];
}];
}
The connection fail doesn't occurs when the user presses the home key. It fails only when the magnetic cover lid is closed or when there is a timeout.

Answer 1

When an app is moved to background, the OS gives the app 5s to finish what it is doing before it is suspended (keeps RAM, but stops the app receiving any messages or doing anything). If you have a task that needs to run to completion when the user presses the home button, you can use a background task. From apple's documentation:
Your app delegate’s applicationDidEnterBackground: method has
approximately 5 seconds to finish any tasks and return. In practice,
this method should return as quickly as possible. If the method does
not return before time runs out, your app is killed and purged from
memory. If you still need more time to perform tasks, call the
beginBackgroundTaskWithExpirationHandler: method to request background
execution time and then start any long-running tasks in a secondary
thread. Regardless of whether you start any background tasks, the
applicationDidEnterBackground: method must still exit within 5
seconds.
Note: The UIApplicationDidEnterBackgroundNotification notification is
also sent to let interested parts of your app know that it is entering
the background. Objects in your app can use the default notification
center to register for this notification.
From http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html

Answer 2

USE Reachability code Try this code to save data once downloaded:
-(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];
}