iPhone Game Development

The Data Store

The final feature we must add to our framework is the ability to store and load data, such as the player’s sound preferences and game progression.

On some platforms, we would be required to create a binary file format to store our data manually using filesystem I/O; however, the iPhone provides the NSUserDefaults API, which allows us to store key-value pairs (similar to the Registry in Windows) of the following types: NSData, NSString, NSNumber, NSArray, and NSDictionary. We have added an interface to perform these tasks easily in ResourceManager.

Storing Simple Data

The simplest data we will want to store is a Boolean variable to indicate whether the user wants game sounds to be on or off. We can store it as an NSNumber in the following manner:

[g_ResManager storeUserData:[NSNumber numberWithBool:TRUE]
              toFile:@"soundPrefs"];

This will save the NSNumber value of TRUE with a key name of "soundPrefs". Then we can exit the application knowing that value has been saved to disk. To retrieve it the next time we start up, we’ll use the following code:

BOOL mySoundPref = [[g_ResManager getUserData:@"soundPrefs"] boolValue];

This will load the NSNumber value associated with the key "soundPrefs" and convert it to a BOOL, which will have a value of TRUE because we stored it on our previous application run.

You can use this method for any of the data types, leading to more interesting combinations. For instance, to store a list of high scores, you could create an NSDictionary whose ...