Significant performance problem loading images in Ribbit

Question

Hi there,

The Ribbit tutorial was how I learned to interact with parse. I learned from Ribbit to load images like this:

- (void)viewDidLoad
{
    // ...
    PFFile *imageFile = [self.message objectForKey:@"file"];
    NSURL *imageFileUrl = [[NSURL alloc] initWithString:imageFile.url];
    NSData *imageData = [NSData dataWithContentsOfURL:imageFileUrl];
    self.imageView.image = [UIImage imageWithData:imageData];
    // ...
}

I recently discovered another way of doing the same thing, which is much faster:

- (void)viewDidLoad
{
    // ...
    PFFile *imageFile = [self.message objectForKey:@"file"];
    self.imageView.image = [UIImage imageWithData:[imageFile getData]];
    // ...
}

Please correct me if I'm wrong, but I think that the first version is making an unnecessary round trip to the internet to retrieve data, even though the data is already available on the PFFile.

Answer 1 · 2014-07-24T07:54:03Z

July 24, 2014 7:54am

Hi Hani,

The getData method might seem faster because it is trying to access the file from cache first and, if not found there, it will grab it from Parse. If you have a look at the PFFile.h from Parse's framework you will see the comment for the getData method:

/*!
 Gets the data from cache if available or fetches its contents from the Parse servers.
 @result The data. Returns nil if there was an error in fetching.
 */
- (NSData *)getData;

The first piece of code you have always grabs the data from Parse without any caching and it may seem slower. With Parse you can use their caching mechanism and it'll speed up your app or you can always use a 3rd party library, or create one yourself, for caching files on your device. A nice one is SAMCache written by one of the teachers here at Treehouse, Sam Soffes, found here: https://github.com/soffes/SAMCache - It's really nice and easy to use.

Answer 2 · 2014-07-27T21:01:04Z

July 27, 2014 9:01pm

Thank you for explaining Robert! You're right that I mistook the caching as actually being faster, when in reality both methods take the same time fetch the image from the web. It's handy to know this, thank you!

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Hani Sharabash

Hani Sharabash

Significant performance problem loading images in Ribbit

2 Answers

Robert Bojor

Robert Bojor

Hani Sharabash

Hani Sharabash