How to call a web service only once for each table UITableViewCell?

Question

I have an application which lists some states (e.g Assam, Andhra, Pradesh etc). When a state is selected, the next view show hospitals located in that particular state in a table view. The hospital names are loaded from a database using web service. This is done so far, no worries.

My problem is: Suppose I have listed hospitals for a state. I go back and select the same state again, the web service is called again and user has to wait for the data. So this is not a good idea. I don't want to call the web service again if I select the same state. How to store data and display it if state selection is same?

Answer 1

You can use NSURLRequestReturnCacheDataElseLoad as the cachePolicy of NSURLRequest.

As Apple stated:

NSURLRequestReturnCacheDataElseLoad Specifies that the existing cache data should be used to satisfy a URL load request, regardless of its age or expiration date. However, if there is no existing data in the cache corresponding to a URL load request, the URL is loaded from the origin source.

Answer 2

to a void calling web service each time , put the result you get from WS in an 2D NSMutableArray attribute of the AppDelegate ,
and each time the user select a state ,verify if the array corresponding to your state is nil

Answer 3

Also SQLite/CoreData may be an approach you might want to consider storing data for a longer and permanent basis.

If currentDate != serverLastUpdatedDate then you can download data from server, you can store data in the form a plist for each rowtext for a quicker implementation. Have a look at the below ways of implementing it.

plist Setting up a plist to store application data (not settings) for an iPhone game

SQLite http://www.techotopia.com/index.php/An_Example_SQLite_based_iOS_4_iPhone_Application

CoreData http://developer.apple.com/library/ios/#DOCUMENTATION/DataManagement/Conceptual/iPhoneCoreData01/Introduction/Introduction.html

Answer 4

Save your data in NSUserDefault

    NSUserDefaults * defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:hospitalAry forKey:@"Hospital"];
    [defaults synchronize];