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William Falcon
William Falcon

Reputation: 9813

run a process in the background while user can still use the UI

I am attempting to run a database fetch process in the background without locking the user interface.

Currently I have a button that does this, but I would like it to be automatic so that it can get more results as user is browsing current results.

Here is the code that the button does, I would like to make this automatic and not lock the UI. Also if there is a way to pause the process, but continue where it left off if user goes to another screen that would also be very useful.

Thanks in advance!

-(IBAction)continueUpdatingResultsButtonPressed:(UIButton*)sender{
[findMoreButton removeFromSuperview];
[self continueFindingMoreRecipes]; //(do this in background without locking screen)
[self loadRefreshButton];//At completion load this button (a blinking button) to refresh the cells with new results

}

Upvotes: 3

Views: 747

Answers (4)

Rob
Rob

Reputation: 437612

It strikes me (especially since you are, by your own admission, "very new to programming") that it might not be prudent to pursue GCD to prefetch data in a background queue, make sure you coordinate the background queue's database operations with the foreground's database operations (possibly via something like FMDB's FMDatabaseQueue or something equivalent), gracefully handle pausing this operation as you go to other screens (as you indicated in your question) and making sure you don't cause retain cycles in the process.

To make matters worse, I gather that this is all in pursuit of a possibly questionable goal, if I understand you correctly, to retrieve 10,000 recipes in the background. Don't get me wrong. You certainly can design all of the background operations like we've outlined, but I think you should stop and ask yourself whether that's the right design for your business problem.

I might suggest an infinitely easier solution. Just load your tableview with the first x recipes, and as the user scrolls down, when you start to approach the end of the tableview, detect that fact and retrieve the next x records and add them to the tableview. But any user interface that is expecting the user to flip through 10,000 entries doesn't pass the smell test. When I think of a database with 10,000 entries, I think of something more like a imdb/wikipedia/google/facebook-like user interface rather than a contacts-style user interface.

Regardless, you almost certainly don't want your app just endlessly retrieving recipes in the background. You can solve your UI performance issue, but maybe replace it with memory management issues. And you're going to design a complicated system architecture when it's not entirely clear whether your recipe app requires that.

Upvotes: 0

Live2Enjoy7
Live2Enjoy7

Reputation: 1105

Use grand central dispatch. Create a new queue, dispatch it with a block and when you need to update, call dispatch get main queue. There is no way to pause this once the queue has been dispatched though. Maybe load recipes into intermediary then update as needed.

Look for some gcd tutorials there are a few decent ones there.

Would give you more code but I'm typing on iPhone.

Upvotes: 2

rmaddy
rmaddy

Reputation: 318814

A typical pattern you can use is something like this:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // perform data processing here (done in the background)

    dispatch_async(dispatch_get_main_queue(), ^{
        // update user interface here (done on the main thread)
    });
});

Upvotes: 6

That Guy
That Guy

Reputation: 56

You could do batch requests where you cache the next X amount of answers every time your UI got with in Y of the current end. Depending on what you are using a lot of databases have protocols that can help you batch cache easily. Good luck!

Upvotes: 2

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