Question

I would like to save an NSArray either as a file or possibly use user defaults. Here’s what I am hoping to do.

1. Retrieve already saved NSArray (if any).
2. Do something with it.
3. Erase saved data (if any).
4. Save the NSArray.

Is this possible, and if so how should I do this?

Answer 1

NSArray provides you with two methods to do exactly what you want: initWithContentsOfFile: and writeToFile:atomically:

A short example might look like this:

//Creating a file path under iOS:
//1) Search for the app's documents directory (copy+paste from Documentation)
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
//2) Create the full file path by appending the desired file name
NSString *yourArrayFileName = [documentsDirectory stringByAppendingPathComponent:@"example.dat"];

//Load the array
NSMutableArray *yourArray = [[NSMutableArray alloc] initWithContentsOfFile: yourArrayFileName];
if(yourArray == nil)
{
    //Array file didn't exist... create a new one
    yourArray = [[NSMutableArray alloc] initWithCapacity:10];

    //Fill with default values
}
...
//Use the content
...
//Save the array
[yourArray writeToFile:yourArrayFileName atomically:YES];