Email attachment doesn't work as file hasn't finished saving? - ios

Question

I have a function which saves the data extracted from a local SQLite DB to a .CSV file.
My problem is that this function also triggers another which attaches the file to an email and sends it. As the file has not yet finished saving the attachment is sent as an empty file.
Is there anyway I can check if the file has finished saving before attaching it to the email? Please see my function below:
// When the tick is visible within the animation...
// Play the bellToneSound.
AudioServicesPlaySystemSound(bellToneSound);
// Creates a temporary GPS object that we will use to save our database as a .CSV file.
GPS *saveGPS = [[GPS alloc] init];
// Finds the phone's documents directory and creates a file path in order create a new file/folder there.
NSError *error = nil;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *dataPath = [documentsDirectory stringByAppendingPathComponent:#"/Jobs"];
if (![[NSFileManager defaultManager] fileExistsAtPath:dataPath]){
[[NSFileManager defaultManager] createDirectoryAtPath:dataPath withIntermediateDirectories:NO attributes:nil error:&error];
}
NSString *filePath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:#"/Jobs/%#.csv", proposalNumber]];
// Creates our new file, with a name matching "jobNo.csv" overrites old one if it already exists.
[[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
// Creates a file handler which will allow us to write to our file.
NSFileHandle *myHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
// Creates and writes the first line to our CSV file, which tells the program reading it what the column titles are.
NSString *csvTitleString =#"Source/Monitor, Latitude, Longitude";
[myHandle writeData:[csvTitleString dataUsingEncoding:NSUTF8StringEncoding]];
// Creates initializes another string object which will hold each line we want to write.
NSString *csvString = [[NSString alloc] init];
// Declares an array and fills it with all GPS objects found in our Database.
NSArray *allGPS = [[NSArray alloc]initWithArray:[database getAll]];
// While the current index value is less than the length of the array write the GPS values into our file then take a new line.
for(int i=0;i<(allGPS.count);i++){
saveGPS = [allGPS objectAtIndex:i];
csvString = [NSString stringWithFormat:#"\n %# %d, %#, %#", [saveGPS sourceMonitor], [[saveGPS positionNo] intValue], [saveGPS latitude], [saveGPS longitude]];
[myHandle seekToEndOfFile];
[myHandle writeData:[csvString dataUsingEncoding:NSUTF8StringEncoding]];
}
}
UPDATE
Here is the code you asked for.
NSString *docsDir;
NSString *realpath;
NSArray *dirPaths;
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = dirPaths[0];
realpath=[[NSString alloc] initWithString:[docsDir stringByAppendingPathComponent: [NSString stringWithFormat:#"/Jobs/temp.csv"]]];
NSFileManager *filemgr = [NSFileManager defaultManager];
if ([filemgr fileExistsAtPath: realpath ] == YES)
{
[self checkIfSaved];
}
else
{
NSLog(#"file found");
// Checks if the device can send email.
if([MFMailComposeViewController canSendMail]){
// Sets the subject to data from (our current proposal number).
[mail setSubject:[NSString stringWithFormat:#"Data from %#", proposalNumber]];
[mail setMessageBody:#"Please see the attached .CSV file." isHTML:NO];
// Finds the .CSV file we just saved, and attaches it to the email.
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *filePath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:#"/Jobs/%#.csv", proposalNumber]];
NSData *attachment = [NSData dataWithContentsOfFile:[NSString stringWithFormat:#"%#", filePath]];
[mail addAttachmentData:attachment mimeType:#"text/csv" fileName:[NSString stringWithFormat:#"%#",proposalNumber]];
// Opens up the email screen.
[self presentViewController:mail animated:YES completion:NULL];
}
else
{
// Tells the user that there device cannot send email.
NSLog(#"This device cannot send email");
// Creates a popup window to inform the user that their location wasn't updates.
UIAlertController* alert = [UIAlertController alertControllerWithTitle:#"Error"
message:#"Unable to send email. Have you set up a mail account on this device?"
preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction* dismissAction = [UIAlertAction actionWithTitle:#"Dismiss" style:UIAlertActionStyleCancel handler:^(UIAlertAction * action) {}];
alert.view.tintColor = [UIColor orangeColor];
[alert addAction:dismissAction];
[self presentViewController:alert animated:YES completion:nil];
}
}

Answer 1

You need to arrange your code so that the email part doesn't start until after the file has been completely saved. There are a number of ways to do that:
polling: You can keep checking the status of the file until you find that the operation is complete. Sometimes polling is unavoidable, but it's generally the worst option. Don't go this route.
completion routine: The file saving method could take a parameter that is a block of code to execute when the saving is done. This is very common, and you'll see it all over the place in the various iOS frameworks. For example, NSURLSession has a -dataTaskWithURL:completionHandler: method. When the requested data has been loaded, the completion handler is called.
serial execution: Put your file-saving code in one block and your mail sending code in another block. Then you can use NSOperationQueue or use Grand Central Dispatch directly to schedule both blocks in a serial queue, so that the second block won't start until the first one is finished.
Both the completion routine approach and the serial execution approach are reasonable ways to ensure that you don't start the e-mail process until the file is saved, so pick whichever seems easiest to you.