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I'm using the NSURLConnection class to download a large file in my iPhone application, but it crashes every so often because it's using too much memory. I'm doing the usual NSURLConnection usage, to append the received data to a NSMutableData object.

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.fileData appendData:data];
}

Then after I finish downloading the whole file, I save it to a local temporary file, and read it as a mapped file like this:

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // save the downloaded data into a temporary file
    NSString *tempPath = NSTemporaryDirectory();
    NSString *tempFile = [tempPath stringByAppendingPathComponent:@"temp.pdf"];
    [self.fileData writeToFile:tempFile atomically:YES];
    NSData *mappedData = [NSData dataWithContentsOfMappedFile:tempFile];

    NSURL *baseURL = [NSURL URLWithString:@"http://mydomain.com"];
    [webView loadData:mappedData MIMEType:@"application/pdf" textEncodingName:@"UTF-8" baseURL:baseURL];
}

What can I improve here to avoid these memory usage problems?

jpm
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    I wrote a library for that, I'm putting it here hoping it will be useful to some people, or inspire them writing their own solution. If you are ok with it of course. https://github.com/thibaultCha/TCBlobDownload – thibaultcha May 31 '13 at 09:35

3 Answers3

40
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse*)response {

    filename = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:save_name]; // filename is in .h file

    [[NSFileManager defaultManager] createFileAtPath:filename contents:nil attributes:nil];
        file =
[[NSFileHandle fileHandleForUpdatingAtPath:filename] retain];// file is in .h 

//if (file)     {
//
//      [file seekToEndOfFile];
//  }
 }

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSD
ata *)data {

 if (file)  { 

        [file seekToEndOfFile];

    } [file writeData:data]; 

}

- (void)connectionDidFinishLoading:(NSURLConnection*)connection { 

[file closeFile]; 

}
Paresh Thakor
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  • Are there drawbacks to using the simpler didReceiveData() below posted by Mobihunterz? Seems simple and clean. – drfence May 15 '12 at 00:45
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    DRFENCE the didReceiveData() is good but it opens and closes the particular file 'file1' each time when this function is called. And the function will be called numerous times while downloading larger files. So, execution might be a bit slow due to overhead of open/close each time. While the above function just writes to the file in this method and opens and close the file only at beginning and ending. – Paresh Thakor May 16 '12 at 12:17
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    isn't the seekToEndOfFile in connection:didReceiveData: unnecessary? writeData: docs say `If the receiver is a file, writing takes place at the file pointer’s current position. After it writes the data, the method advances the file pointer by the number of bytes written.` – qix Nov 20 '12 at 01:06
  • @Linus Thanks for your mark but I did not checked it removing the stuff. – Paresh Thakor Nov 20 '12 at 07:00
17

If it's that large, why not write it to the file as it comes in, rather than keeping it in an NSData object?

Ben Gottlieb
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    jpm: you'll want to check out the NSFileHandle class. – Daniel Dickison Mar 08 '09 at 17:00
  • Ben, you are totally right. Rewrote my class using `NSFileHandle` to avoid keeping the whole file in memory, and seems to work much better now. Thanks Daniel for the tip too! – jpm Mar 08 '09 at 18:59
6

i'm using

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    filename = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:save_name];
    NSFileHandle *file1 = [NSFileHandle fileHandleForUpdatingAtPath: filename];
    [file1 writeData: data];
    [file1 closeFile];
}
Vladimir
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Paresh Thakor
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