NSKeyedArchiver archivedDataWithRootObject:

Is the parameter for NSKeyedArchiver archivedDataWithRootObject: supposed to be the array I a开发者_JAVA技巧m trying to save, or the array converted into NSData?

Yuji's answer is right. but more accurately, your element of an array have to implement protocol and fillin your own code to methods initWithCoder: and encodeWithCoder: like:

- (id)initWithCoder:(NSCoder *)decoder {
    if (self = [super init]) {
        self.title = [decoder decodeObjectForKey:@"title"];
        self.author = [decoder decodeObjectForKey:@"author"];
        self.published = [decoder decodeBoolForKey:@"published"];
    }
    return self;
}
- (void)encodeWithCoder:(NSCoder *)encoder {
    [encoder encodeObject:title forKey:@"time"];
    [encoder encodeObject:author forKey:@"author"];
    [encoder encodeBool:published forKey:@"published"];
}

then you can use the archiver and unchariver like:

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:notes];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:@"notes"];

NSData *notesData = [[NSUserDefaults standardUserDefaults] objectForKey:@"notes"];
NSArray *notes = [NSKeyedUnarchiver unarchiveObjectWithData:notesData];

For more, you can get reference "Archiving Objective-C Objects with NSCoding".

To convert a generic array to an NSData, you need an archiver! If you know how to feed the NSData, you know how to use NSKeyedArchiver. So:

NSArray* array= ... ;
NSData* data=[NSKeyedArchiver archivedDataWithRootObject:array];

Of course all elements in your array needs to implement encodeWithCoder:.