Question

I’m using URLScheme and I need to send serialized NSDictionary from my app A to my app B.

In the app A, I’m using NSKeyedArchiver to serialize my NSDictionary into a NSData

    NSDictionary *myDictionary = [NSDictionary dictionaryWithObjectsAndKeys:@"This is value 1", @"key1", 
                                    @"value 2", @"key2",
                                    @"value3", @"key3", 
                                    @"", @"key4", 
                                    @"value5", @"key5", 
                                    @"value 6", @"key6", 
                                    nil];
NSMutableData *data = [[NSMutableData alloc] init];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:myDictionary];
    [archiver finishEncoding];
    [archiver release];

    NSString *bytes = [[[NSString alloc] initWithData:data
                                             encoding:NSASCIIStringEncoding] autorelease];

In the app B, I’m using NSKeyedUnarchiver

NSData *data = [[NSString stringWithFormat:@"%@", val] dataUsingEncoding:NSASCIIStringEncoding];        
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
NSDictionary *myDictionary = [[unarchiver decodeObject] retain];
[unarchiver finishDecoding];
[unarchiver release];

My serialized NSDictionary looks like:

bplist00Ô01T$topX$objectsX$versionY$archiverÑR$0¯
!”#$%&'()U$nullÓ ZNS.objectsWNS.keysV$class¦
¦Tkey2Tkey5Tkey3Tkey1Tkey6Tkey4Wvalue 2o@

And it looks like I can’t convert this NSString to NSData and get my NSDictionary back.

NSData is NULL after the [dataUsingEncoding:dataUsingEncoding:NSASCIIStringEncoding].

Answer 1

Why on earth are you sending bytes as a NSString – that’s never going to work!

(a) NSString is for encoded textual data – i.e. data that follows a specific set of rules.

(b) NSData is for a series of bytes that are just bytes.

You have (b), not (a).

Send NSData objects and don’t convert to/from NSString at all.

---

EDIT what about URL paramters?

OK, so my answer above was a little too black and white.

If you really need to convert between data and string, take a look at base64 encoding – it will give you a safe string representation of your data at the expense of size.

There’s a few libraries outt here that can convert for you – try this one : https://github.com/nicklockwood/Base64

However, what will happen if you encode a dictionary on an iOS6 device and decode it on iOS5 – you can’t be 100% certain that will work. You might be better off writing your own coding/decoding methods that convert the dictionary to a string and back again. If it’s for a URL, why not just use URL parameters i.e. x=5&name=Bob?