Custom iOS address book. Need advices about data structures and performance

Question

I am currently developing a voIP app and I am really stuck with the address book.

Because of the custom design, the native address book does not fit in my app. Besides, I want to add some extra data not present in the native address book. But this is leading into some problems which I've separated into two sections:

1. Data structures:

In a section of my app I need to show to the user all his address book contacts with additional information (if the user has the same app and it's online, for example).

Right now I'm getting all the info from the Address Book api and loading it in an array directly (which is accessed by the tableView:cellForRowAtIndexPath:), but not displaying the custom information I was talking about. I don't know if its worthwhile to store all the address book info in a sqlite data base (where I'd be able to add the extra information easily) or if I should store only that extra information in a file or something.

The biggest problem of storing it in a data base is that the contact's picture is heavy enough to get a wasting-memory data base. I thought to store only a reference (the ABRecordID) and then to gather the related info from the address book instead of the data base, but the Apple documentation of the Address Book api says the ABRecordID is not guaranteed to remain the same, so it could cause my data to appear next to wrong contact data.

Any idea?

2. Performance:

The second big problem with this custom address book is that... the iOS table views are too 'manual' compared to the Android ones, for example. You need to have the data stored somewhere so that when the tableView:cellForRowAtIndexPath: method gets called you return that data. You can also load that data inside this method, but this makes it very slow.

The problem here is that preloading all the data in memory is dangerous, because a person may have 40 contacts or 2000 (and maybe he/she has taken a picture for each of them, which will be much more memory-consuming). If the iOS device runs out of memory the system will kill the app. The data base approach has no memory problems, but making queries for each cell to appear is so slow that it becomes unacceptable.

Again, I need ideas for this. Can't find a tradeoff between performance and memory consumption.

Please, don't ask for code because I'm not allowed to post it. I'd really appreciate your advices. Thank you in advance!

Answer 1

1. Data structures: Along with the recordref you should store the name phone number and email address. Nothing else in your data store. If one of the three vales change and the other two remain the same update the changed value. The recordref can change during a restore of a device for many users at once but the name email and phone won't. If the user changes a name or email or phone they won do it across many users at once. Once in a while you end up with a recordref that does not match up with email and phone say, the contact may have changed employers so then show a list of close matches and ask the user to select one.

As far as some one having 1000s of contact I would use paging. Load 100 or 200 at a time in to an array with current row displayed in the table view as middle of your array index. Once the user scrolls 20-30 records update the records in your array from address book. Your going to be spending a lot time resaving data just to go through the collection comparing and trying to keep it up to date. You should be able to store quite a few records long as your not keeping the user images in memory, for that you should let the table view handle it. Get image and assign to cell when you get the notification about the cell about to become visible. Even then I would put a short wait before loading the image, because if the user is scrolling fast the cell will just fly by and you'll get notified that the cell scrolled out and you can release the image data. If the user is scrolling slowly then the short wait/sleep will pass and the image should show up for each cell.

I don't know how much meta your planning on storing in your app wrapping the contacts but if you should create two tables for the contact object, one with 3-4 indexed columns that will allow for faster querying and a second to hold the rest that loaded only when users viewing the contact in a detail view. Can't get too much into a tableviescell, unless your on the iPad.

Hope that helps.