How can I update data in iPhone app

Question

I create an app, with data store in plist. Now what are the ways I can update the data? Maybe if I create a webpage and retrieve my data from it instead of storing in plist? Or is there a way I can update my data when I plug into iTunes? Or any other suggestion? What I want to achieve is a way of updating my data once user have download the app.

Answer 1

NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *dir = [path objectAtIndex:0];
NSString *filePath = [dir stringByAppendingPathComponent:@"my.plist"];

NSMutableDictionary *localDictionary;
NSUrl *remoteUrl = [NSURL URLWithString:@"http://server.com/my.plist"];
NSMutableDictionary *remoteDictionary = [NSMutableDictionary dictionaryWithContentsOfURL:remoteUrl];
if(remoteDictionary != nil) {
     [remoteDictionary writeToFile:filePath atomically:YES];
     localDictionary = remoteDictionary;
}
else {
     localDictionary = [NSMutableDictionary dictionaryWithContentsOfFile:filePath];
     if(localDictionary == nil) localDictionary = [NSMutableDictionary dictionary];
}

This will try to obtain a copy of my.plist from http://server.com/, on success it will write it to the disk and point localDictionary to it, on error it will try to read from disk (e.g. downloaded earlier when there was a connection), if there is no file on disk it will create a empty NSMutableDictionary. Either way localDictionary will point to a NSMutableDictionary in the end.

This is very simple and will request the file every time the code is run. You could e.g. use NSFileModificationDate (obtained by NSFileManger attributesOfItemAtPath:error:) and NSDate to determine if a update is necessary. Or for big files versioning would make sense as well, having a small file containing the version of the bigger file - getting the small file from the server (e.g. with NSString), checking whether the cached version file contains a lower version number, if so get the big file. It always depends on how often the content is refreshed.

See full documentation: NSDictionary, NSString, NSFileManager, NSDate

Answer 2

Plists are not easily modifiable since you have to read them back into memory, make the changes and write them back to the file.

For writing the plists look at NSDictionary's or NSArray's writeToFile:atomically: method. Remember your plist is basically an XML made up from NSArrays, NSDictionaries, NSStrings and NSData, and you'll always want to write out the root node.

Alternatively look for other ways of storing your data: user defaults or sqlite databases. Storing data 'in the cloud' makes sense only in some cases, like if you want to share it between different devices or want to update it remotely. It's best to avoid it if possible.