UI freeze while saving images

Question

I'm trying to save a NSDictionary containing 30 images. I'm calling the method to save the dictionary in the viewDidDisappear of my ViewController. The problem is that the UI freeze while saving. It's a small lag, less than a second, but a bit annoying. Do you have any ideas to make it more fluid? Maybe I should save the dictionary asynchronously, maybe in a block, but I don't know well how to use them.

Here's my saving et getting methods :

+ (NSDictionary*)getProgramImages{
    NSString *path = [DataManager getProgramImagesFileDirectory];
    NSDictionary *programImages = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

    return programImages;
}

+ (void)saveProgramImages:(NSDictionary*)programImages{
    NSString *path = [DataManager getProgramImagesFileDirectory];

    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:programImages];
    [data writeToFile:path options:NSDataWritingAtomic error:nil];
}

Thanks a lot for your help!

Boris

The issue is that you're calling the save functions on the main thread, which freezes the UI if its too heavy. Read more about threads here: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html — Milo, Jun 13 '14 at 02:31

score 2 · Accepted Answer · answered Jun 13 '14 at 02:15

You could try wrapping your function call using the below code, which uses Grand Central Dispatch to run that code on a background thread. Not able to test at the moment to see if that could solve your issue or not.

dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // call that function inside here
});

score 1 · Answer 2 · answered Jun 13 '14 at 02:15

1

Maybe dispatch_async could help you to smoothen the code running on main thread.

 dispatch_async(dispatch_get_main_queue(),^{
        //your code goes here
    });

answered Jun 13 '14 at 02:15

HelmiB

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Quang Hà · Answer 3 · 2014-06-13T02:27:56.727

1

There're many ways to solve your problem. You should read this Concurrency Programming

Grand Central Dispatch is a good choice.

edited Jun 13 '14 at 02:27

answered Jun 13 '14 at 02:20

Quang Hà

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UI freeze while saving images

3 Answers3