asynchronous calls to database in ios

ashwinr87 · 10-03-2011, 12:54 PM

I have 4 UITableView's on my iPAD application. I load the data on them using a function

Code:

loadData

,which is there in all the 4 TableViewController.m files, which makes calls to the database.

So, I would be doing something like this

Code:

[aView loadData];
[bView loadData];
[cView loadData];
[dView loadData];

Where aView, bView, cView and dView are the view controllers of the UITableView's.

However, the database calls happen synchronously and hence only after the data is retrieved from the [aView loadData] function, does the [bView loadData] function get called and so on.

This affects my performance.

I would like to know if there is a way I can asynchronously make calls to the database/ asynchronously make calls to functions which calls database.

It would be great if someone could help me out with this.

**smithdale87** · 10-03-2011, 01:15 PM

Have you tried spawning a new thread for each?

ashwinr87 · 10-03-2011, 01:20 PM

Quote:

Originally Posted by smithdale87

Have you tried spawning a new thread for each?

I was thinking about that, but I am not sure how to do that and was looking for guidance on how to do the same.

nobre84 · 10-03-2011, 03:49 PM

You can spawn a new thread to run your method using

Code:

[aView performSelectorInBackground:@selector(loadData)]

Beware tho, that the method (loadData) must not directly mess with the main thread (i.e no UI objects). If its needed, it must be synchronized with the main thread using performSelectorOnMainThread

Duncan C · 10-03-2011, 07:06 PM

Quote:

Originally Posted by ashwinr87

I have 4 UITableView's on my iPAD application. I load the data on them using a function

Code:

loadData

,which is there in all the 4 TableViewController.m files, which makes calls to the database.

So, I would be doing something like this

Code:

[aView loadData];
[bView loadData];
[cView loadData];
[dView loadData];

Where aView, bView, cView and dView are the view controllers of the UITableView's.

However, the database calls happen synchronously and hence only after the data is retrieved from the [aView loadData] function, does the [bView loadData] function get called and so on.

This affects my performance.

I would like to know if there is a way I can asynchronously make calls to the database/ asynchronously make calls to functions which calls database.

It would be great if someone could help me out with this.

Why do you call loadData on a table view of a view controller that isn't the front view controller?

That's wrong for a number of reasons.

First, nobody but the owning view controller should manipulate its views directly. Doing that is a huge violation of encapsulation in object oriented programming. It's corrupts the MVC design pattern.

Second, the other table views may not even be loaded if they are on the frontmost view controller. The system can unload the views of any view controller but the front one at any time to free up memory.

Third, it's taking time to do something that doesn't have any visible result, and causing the UI on the current view controller to lag.

You should add a "dataHasChanged" method to each of your view controllers, and call that. Then, when the view controller's viewWillAppear (or viewDidAppear) method gets called, it can call reloadData itself if its data has changed.)