Below is a code to receive data from a Bluno Beetle BLE:
/* Data received */
else if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:BLECharacteristic]]){
NSString *data = [[NSString alloc] initWithData:characteristic.value encoding:NSUTF8StringEncoding];
NSLog(#"Received Data = %#", data);
[_receiveText setText:data];
}
However, if I want to display multiple data values, is there a way for me to split the received text/data?
For example I want to display a number and a text, and the Arduino sends over a string. New to coding, so your help and patience will be appreciated!
is there a way for me to split the received text/data?
Yes, of course. You can do whatever you like to the data once you've got it. Take a look at the NSString documentation and you'll find plenty of methods for splitting and otherwise extracting data from strings. Some examples: -componentsSeparatedByString:, componentsSeparatedByCharactersInSet:, -stringByTrimmingCharactersInSet:, -substringWithRange:, etc. There are also other Foundation classes that can help, like NSScanner and NSRegularExpression.
New to coding, so your help and patience will be appreciated!
Reading the fine manual should be your first move no matter what your experience level is. The documentation for Apple's frameworks is generally excellent, and it includes many guides and introductory "getting started" documents that make it easy to get up to speed.
I wave read many articles about parsing a json via an Http request but almost none answers the question about what is the most straight forward way to parse o local json string. I found some deferent solutions here Deserializing local NSString of JSON into objects via RestKit (no network download) some of them work some others don't. Is there any "official" RestKit support for local JSON string deserialization?
Fortunately Apple provides "NSJSONSerialization" class from iOS 5.0. to serialise your data.
Step 1 : convert your local JSON string to "NSData"
NSString *strLocalJSON = #"{data= "some data"}"; //just for ex. may not be valid one
NSData *dataJSON = [str dataUsingEncoding:NSUTF8StringEncoding];
Step2:
id jsonobject= [NSJSONSerialization JSONObjectWithData:dataJSON options:NSJSONReadingMutableContainers error:nil]; // resulting object may contain Dictionary or Array depends on your localjson
for further info refer https://developer.apple.com/library/ios/documentation/Foundation/Reference/NSJSONSerialization_Class/Reference/Reference.html
If your JSON is in a file then you use a file:// NSURL when you create your RestKit object manager. Everything else works as normal.
If the JSON is already in code, then you should save it to a file, or why are you needing to do any mapping? Anyway, you could use a combination of NSJSONSerialization and RKMappingOperation.
I think I need some assistance in figuring out the correct NSJSONSerialization option to make my problem go away.
On my app I allow the user to select an image from the gallery - the image undergoes the following:
NSData *imageData = UIImageJPEGRepresentation(self.profileImageView.image, 0.0);
then
NSString *stringOfImageData = [imageData base64EncodedStringWithOptions:0];
before it is serialized like this:
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:postDict
options:NSJSONWritingPrettyPrinted
error:&error];
and then sent to my REST API. I then decode it in python using base64 like so:
profileImageData = base64.b64decode(request.json['image'])
It is then loaded in GridFS (mongodb). On extracting the data to send back to the app I first encode in base to base64 before using dumps() to send it back:
dumps(base64.b64encode(fs.get_last_version(request.json['userID']).read()))
Within iOS after receiving the data it goes through the below de-serialization:
[NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers|NSJSONReadingMutableLeaves error:&error]
I have narrowed by problem to the last NSJSONSerialization command. After the data is received by the app it is able to print to screen. After the Serialization I get a 'nil' :(
The Serialization and De-Serialization has been working great for strings, integers etc - it just doesn't work when I'm trying to move image data.
Thanks
EDIT: I am able to run a curl request against the API and then using an online base64 to image converter I can see my image. So it definitely means the issues is with the iOS side of decoding a json encoded base64 string.
EDIT: When I repeatedly run the deserialization - every 20th time or so the data is correctly converted. I think the solution might have to be to break up the data coming in.
EDIT: Error:
parsed error:Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (Unterminated string around character 17.) UserInfo=0x109c08790 {NSDebugDescription=Unterminated string around character 17.}
What you don't say is how you are receiving the data. My guess is you are trying to decode the data before you receive all of it, but since I don't know how it's a guess.
To better understand what's going on, try logging the size and hash of the data, to see if the length varies. You can also save each received data object to the file system - put them in the Documents folder and you can access them from your Mac. If the size never varies you will then have to compare a good data object to a bad one.
In fact you can write a little code to save an image as data and a base64 string, upload it, then pull it back, and save it. Now compare the data and strings. Once you find a difference, then look at. What is its offset from the start? How is it different?
When you understand this all you will be able to fix it.
I am making an iOS client for the Stack Exchange API. After a long, drawn out fight I finally managed to implement authentication - which gives me a token I stick into a URL. When the token is valid, the URL looks like this:
https://api.stackexchange.com/2.1/me/associated?key=_____MY_SECRET_KEY______&access_token=_____ACCESS_TOKEN_:)_____
which, when valid, brings me to this JSON in a webpage:
{"items":[{"site_name":"Stack Overflow","site_url":"http://stackoverflow.com","user_id":1849664,"reputation":4220,"account_id":1703573,"creation_date":1353769269,"badge_counts":{"gold":8,"silver":12,"bronze":36},"last_access_date":1375455434,"answer_count":242,"question_count":26},{"site_name":"Server Fault","site_url":"http://serverfault.com","user_id":162327,"reputation":117,"account_id":1703573,"creation_date":1362072291,"badge_counts":{"gold":0,"silver":0,"bronze":9},"last_access_date":1374722580,"answer_count":0,"question_count":4},...
And I get the correct JSON with this code:
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"https://api.stackexchange.com/2.1/me/associated?key=__SECRET_KEY_:)__&access_token=%#", [[NSUserDefaults standardUserDefaults] objectForKey:#"token"]]];
NSData *jsonData = [NSData dataWithContentsOfURL:url];
if (jsonData)
{
NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:nil];
}
When I manually invalidate the token, however, the URL still looks the same, and the page in a browser displays this:
{"error_id":403,"error_name":"access_denied","error_message":"`key` is not valid for passed `access_token`, token not found."}
However, dataWithContentsOfURL: is always nil. Why? What am I doing wrong?
I do get an NSError returned:
Error Domain=NSCocoaErrorDomain Code=256 "The operation couldn’t be completed. (Cocoa error 256.)" UserInfo=0x1dd1e9f0 {NSURL=https://api.stackexchange.com/2.1/me/associated?key=key((&access_token=token))}
NSCocoaErrorDomain Code=256 actually means a "file system or file I/O related error whose reason is unknown".
Why you get this error is likely because using dataWithContentsOfURL: will not work with that remote URL - or maybe because of the query params which contain the authentication and the token. Thus, you get the "weird" error.
In general, NSData's dataWithContentsOfURL: should only be use to access local file resources.
In order to solve your problem, you should improve your code in two steps:
1) Use NSURLConnection's convenient class method
+ (void)sendAsynchronousRequest:(NSURLRequest *)request queue:(NSOperationQueue *)queue completionHandler:(void (^)(NSURLResponse*, NSData*, NSError*))handler
The block defines what to do with the response data when the request finished. Generally, first check the error parameter, then status code of the response and Content-type - in this order.
2) Replace the former with your own instance method (or one from a third party) with a similar signature but which is much more sophisticated.
Approach #2 enables you to implement and use the following important features
Cancellation
customize authentication in every aspects
load body data to files
process received chunks simultaneous
perform multiple requests in a queue which controls the number of simultaneous connections
and a couple more.
Approach #2 is oftentimes implemented as a subclass of NSOperation and encapsulates a NSURLConnection object (which you need to cancel the connection).
You'll find answers of how to use NSURLConnection in asynchronous mode implementing the delegates. Also, there are third party solutions.
You might find the official documentation invaluable, too:
Using NSURLConnection
For a quick start, you may take a look at my "Simple GET request" class on Gist:
SimpleGetHTTPRequest
This class is NOT based on NSOperation, but it can be modified easily. Consult the official documentation of NSOperation how to make a subclass. This is basically easy, but has a few important things (KVO) which you should get correct.
In my case, adding AppTransportSecuritySettings dictionary into info.plist and setting key AllowArbitraryLoads to true.
Fixed my problem...
Hope it helps new developers.
Your URL might be having a space that's why it returns nil.Just replace the space in URL with a '+' :
stringByReplacingOccurrencesOfString:#" " withString:#"+"
I had this problem when I changed my folder structure. It gave me other NSError codes such as 512 and 4 for any file operations (local and web). The solution was to delete my IOS Simulator folders (Library\Developer\CoreSimulator).
If you are trying to access a remote url via HTTP and using XCode 7 or later you may get a NSCocoaErrorDomain returned from [NSData dataWithContentsOfURL:].
The root cause of this may actually be your "App Transport Security Settings". By default iOS doesn't allow arbitrary loading of URLS.
I am currently going through the Pragmatic iOS 6 book, and am having trouble understanding the following line of code explained in chapter 3 under the section about GCD:
NSJSONSerialization *jsonResponse = [NSJSONSerialization JSONObjectWithData:data options:0 error:&jsonError];
//... some code here
NSArray *tweets = (NSArray *) jsonResponse; //<-- this line
Is it saying that the NSJSONSSerialization object could automatically return an instance of NSSArray, which is then stored in the tweets? I checked the Apple docs, but only saw items on restrictions using NSJSONSerialization, but not what objects it could then get converted to.
Thanks!
NSJSONSerialization can take a chunk of JSON data and turn into objects and it can do the same in the other direction that is by taking objects and converting them into the JSON data.
For easy understanding of NSJSONSerialization and interaction with Twitter, i would recommend you to use THIS and THIS tutorials.
Hope this helps!