iOS - writeToFile from NSData completion handler - ios

Question

I am getting bytes of a file from a webservice, my goal is to get these bytes, put them into NSData and then write into a file, once the writeToFile is 100% complete, I would then display the file (its a PDF, can be up to 6 pages) in QLPreviewController.
I am able to get the bytes from the webservice and put them into NSData like so:
NSArray *byteArray = [dataSource.areaData GetPDFFileData:[NSString stringWithFormat:#"%#",encodedUrlStr]];
NSData *data;
for (NSDictionary *dict in byteArray) {
NSString *base64 = dict[#"data"];
data = [[NSData alloc] initWithBase64EncodedString:base64 options:0];
}
Now I am trying to write the file like so:
if (data)
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
filePath = [NSString stringWithFormat:#"%#/%#", documentsDirectory,PDFFile];
[data writeToFile:filePath atomically:YES];
}
Now what I am trying to do is have some sort of completion handler so nothing else happens until the file is completely written. What would be the best way to do this?
I am also starting to look into NSFileHandle, would that be a better solution?

Answer 1

use NSFilePresenter to monitor for changes to the file
and use a NSFileCoordinator to write to it
in mock code:
NSFilePresenter *p = [NSFilePresenter presenterWithFile:f];
[p signupForChangeNotificationsOrSetDelegateOrWhatever....];
//write
NSFileCoordinator *c = [NSFileCoordinator coordinatorWithPresenter:p];
[c coordinate writeData....]
... called back by p cause we changed

Answer 2

No need to worry about completion if this runs in main queue it's serial , but it's better to save in background queue and read content to verify and present in main Queue
DispatchQueue.global(qos: .background).async {
print("This is run on the background queue")
if (![[NSFileManager defaultManager] fileExistsAtPath:filePath])
{
NSLog(#"not exists");
NSData *fileContents = [#"" dataUsingEncoding:NSUTF8StringEncoding];
[[NSFileManager defaultManager] createFileAtPath:filePath
contents:fileContents
attributes:nil];
}
else
{
NSLog(#"exists");
}
NSFileHandle *myHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
[myHandle seekToEndOfFile];
NSString*strTowrite=[NSString stringWithFormat:#"%# || %# --- %# \r\n",dt,acion,name];
[myHandle writeabilityHandler];
[myHandle writeData:[strTowrite dataUsingEncoding:NSUTF8StringEncoding]];
DispatchQueue.main.async {
NSString*content=[[NSString alloc] initWithContentsOfFile:filePath
encoding:NSUTF8StringEncoding
error:&error];
if(content)
{
NSLog(#"content is : %# Err : %#",content,error);
// [self sendfile];
}
else
{
NSLog(#"Failed to store the file. Error = %#", error);
}
}
}