NSString from NSData is nil

Question

I try to get an NSString from NSData but I get a nil value. This is my code:

NSString *dataString = [[NSString alloc] initWithData:self.message.data encoding:NSUTF8StringEncoding];

When I log self.message.data I get:

Printing description of self->_message->_data:
<OS_dispatch_data: data[0x17e48290] = { leaf, size = 331233, buf = 0x3aac000 }>

That means my data is not nil…

Can anyone help?

Where is this data coming from and in which format is this data sent? — Pavan, Apr 21 '14 at 20:26
What is outputted if you do `NSLog(@"Class of self->_message->_data: %@", NSStringFromClass([self->_message->_data class]));`? — Rich, Apr 21 '14 at 20:26
The `initWithData:encoding:` method expected an `NSData` object. What is your `self.message.data` object? — rmaddy, Apr 21 '14 at 20:26
Interestingly there's also another [question](http://stackoverflow.com/questions/19434245/how-to-convert-os-dispatch-data-5018112-bytes-into-nsdata-to-put-into-uiimag) around this `OS_dispatch_data`! (Not that I'm saying this is a duplicate!) — Rich, Apr 21 '14 at 20:29
Just noticed my data isn't a regular NSData as I thought. It is OS_Dispatch_Data. What is it? — Nimrod Shai, Apr 21 '14 at 20:30
@NimrodShai see [this question/answers](http://stackoverflow.com/questions/9152851/how-to-convert-dispatch-data-t-to-nsdata) for more information about `OS_dispatch_data` :) — Rich, Apr 21 '14 at 20:31
try using `po [self.message.data description]` in the debugger to get a printed description of the data. That will give insight into whether the data might be in the proper format to create a string out of... — NSGod, Apr 21 '14 at 20:37

skywinder · Accepted Answer · 2014-07-15T07:08:42.410

1

As answer to your question in comments: OS_dispatch_data is dispatch_data_t which has toll-free bridging with NSData on iOS 7 and Mavericks. You can simply cast it to NSData *.

So, in your case you can write:

NSData *dataCast = self.message.data;
NSString *dataString = [[NSString alloc] initWithData:dataCast encoding:NSUTF8StringEncoding];

And now you get the correct string!

In my case it appeared, when AFNetworking cast internal NSMutableData to NSData.

And this simple cast helps me.

UPD: As @Daij-Djan mentioned: If it's not works - try to check your text encoding.

For example if you're yousing NSURLSessionTask:

NSURLSessionTask *task; // Your NSURLSessionTask
NSString *encoding = [[task response] textEncodingName];

In your case (NSUTF8StringEncoding) it should be "utf-8".

edited Jul 15 '14 at 07:08

answered Jul 15 '14 at 06:39

skywinder

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IF the encoding of the text is UTF8 – Daij-Djan Jul 15 '14 at 06:44
@Daij-Djan of course. But question is how convert `OS_dispatch_data` to `NSData`. And I believe that we know the encoding that we use. – skywinder Jul 15 '14 at 06:48
the question is 'NSString from NSData is nil' -- and what do you mean 'we know' – Daij-Djan Jul 15 '14 at 06:50
btw I up voted you because you finally wrote that dispatch data is just an internal representation for NSData - the comments were weird :) – Daij-Djan Jul 15 '14 at 06:51
though as the code you provide is 100% the op's code I guess it is the encoding – Daij-Djan Jul 15 '14 at 06:52
@Daij-Djan w\o this redundant cast I also get the `nil` string. And this simple cast solve my problem. I don't know why. Complier bug?.. :) – skywinder Jul 15 '14 at 07:02
@Daij-Djan Ok, I update answer with your suggestion. – skywinder Jul 15 '14 at 07:09

score 0 · Answer 2 · answered Apr 21 '14 at 20:30

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Try UTF-16 encoding instead. It may be an error converting to UTF-8 if any data in there is not recognized.

answered Apr 21 '14 at 20:30

C_Rod

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NSString from NSData is nil

2 Answers2