How do I convert an NSNumber to NSData?

Question

I need to transmit an integer through GameKit using sendDataToAllPeers:withDataMode:error: but I don't know how to convert my NSNumber to NSData in order to send. I currently have:

NSNumber *indexNum = [NSNumber numberWithInt:index];
[gkSession sendDataToAllPeers:indexNum withDataMode:GKSendDataReliable error:nil];

but obviously the indexNum needs to be converted to NSData before I can send it. Does anyone know how to do this please?

Thanks!

Solution 1

I would not recommend NSKeyedArchiver for such a simple task, because it adds PLIST overhead on top of it and class versioning.

Pack:

NSUInteger index = <some number>;
NSData *payload = [NSData dataWithBytes:&index length:sizeof(index)];

Send:

[session sendDataToAllPeers:payload withDataMode:GKSendDataReliable error:nil];

Unpack (in the GKSession receive handler):

NSUInteger index;
[payload getBytes:&index length:sizeof(index)];

Swift

var i = 123
let data = NSData(bytes: &i, length: sizeof(i.dynamicType))

var i2 = 0
data.getBytes(&i2, length: sizeof(i2.dynamicType))

print(i2) // "123"

Solution 2

To store it:

NSData *numberAsData = [NSKeyedArchiver archivedDataWithRootObject:indexNum];

To convert it back to NSNumber:

NSNumber *indexNum = [NSKeyedUnarchiver unarchiveObjectWithData:numberAsData]; 

Solution 3

Why not send the integer directly like this:

NSData * indexData = [NSData dataWithBytes:&index length:sizeof(index)];
[gkSession sendDataToAllPeers:indexData withDataMode:GKSendDataReliable error:nil];

Comments

[Raj Pawan Gumdal]

You assume that the number is a NSUInteger while unpacking. NSNumber can wrap whole lot of different type of numbers - int, float, double, signed / unsigned. I think that archiving and unarchiving is best approach if programmer is not sure what type of data is stored in NSNumber. I go with Ole's approach.

[Era]

Where do you see NSNumber? I never use NSNumber.

[Raj Pawan Gumdal]

The question asked was for NSNumber created from an integer. So, I guess a general solution for NSNumber would have been more appropriate.

[Sifeng]

@Erik Aigner: do you know how to solve this problem with Swift? Thanks in advance!