Question

So I got an exception while trying to implement NSKeyedUnarchiver because I’m trying to save an array of custom objects with NSUsersDefaults. Because I kept on getting an error saying that I had non-properties in it I decided to archive them into NSData. Now I’m getting this error: “incomprehensible archive”.

Here is how I am archiving (I’ve tested all objects to be null, non of them are):

NSMutableArray *array = [[NSMutableArray alloc] initWithArray:anotherArray];
for (int i = 0; i < array.count; i++) {
    CustomObj *obj = [array objectAtIndex:i];
    NSData *newdata  = [NSKeyedArchiver archivedDataWithRootObject:obj];
    [array replaceObjectAtIndex:i withObject:newdata];
}
NSArray *newArray = [[NSArray alloc] initWithArray:array];
[coder setObject:newArray forKey:@"key"];

Here is how I am unarchiving(again everything is tested for null):

if (!arrayM) { arrayM = [[NSMutableArray alloc] init]; NSLog(@"initialized"); }
else {
    for (int i = 0; i < arrayM.count; i++) {
        NSData *data = [arrayM objectAtIndex:i];
        --> The exception happens here: CustomObj *obj  = [NSKeyedUnarchiver unarchiveObjectWithData:data];
        [arrayM replaceObjectAtIndex:i withObject:obj];
    }
}

Answer 1

You didn’t archive it with NSKeyedArchiver, so why would you expect that you would be able to use NSKeyedUnarchiver to get the data back? The way you want to do it is like this. Make your custom object conform to the NSCoding protocol, and implement its two methods (encode and decode). Then you can archive with NSKeyedArchiver on your array of custom objects. The NSKeyedArchiver will call encodeWithCoder on each object, and any objects it contains (if it is a collection).

EDIT: Call NSKeyedArchiver on the array, not each object. Then when you unarchive it, unarchive it into an array again.