iOS: Running database query in viewDidLoad only works once

Question

So let's see if I can write a clear enough description of my problem...

I'm developing an application for a museum, where the user can find artworks either through an id or by scanning a qr tag... Once either an id is entered or a tag scanned, the application sends the user from the search view, to the info view. The info view gathers information about the artwork from an SQLite database...

My problem is, that in the info view, I call the function from the database class as such:

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSArray *paintingInfo = [[PaintingDatabase database] findPaintingByID];

    (additional code)
}

And I have no problem getting the info... works fine... But my problem is, that if I go back to the search view and enter a new id or scan a new tag, the call/search isn't run again, since the view is still in memory...

So, how would I go about running

NSArray *paintingInfo = [[PaintingDatabase database] findPaintingByID];

every time I enter the view...?

I've tried placing it in viewDidAppear instead, but I get an EXC_BAD_ACCESS error...

Answer 1

I think you are close to answering your own question. Since viewDidLoad only gets called when your view loads, if you are using the same ViewController you will not get the results you are looking for. One option may be to destroy and create a new ViewController each time. This probably would be acceptable, performance-wise. Another option (that you seem to have explored) is to put your code in viewWillAppear. I would probably look into this more, and figure out what is causing your crash.

Answer 2

It's a bit difficult to tell from a brief description, but this feels to me like it's more of an application architecture issue than a problem with a specific bit of functionality.

You might be better off with an alternative approach, running the query from outside the info view, and then update the properties of the view through a delegate method. That's more of an MVC approach - the controller retrieves the data from the model, then passes the data over to the view to be displayed.

As you've described it, it seems like your info view is taking both view and controller functions - which could be why you're running into problems trying to get different data once the initial view is finished with.

The crash doesn't sound like a problem with the view, though - I'd second the advice to track that down and nail it as a separate issue.