parsing NSString data-getting null value - objective-c

Question

I am parsing and NSString value but getting null in console. Please help me with the issue.
NSString *responseData = [[NSString alloc] initWithData:_responseData encoding:NSASCIIStringEncoding];
NSLog(#"Data: %#", responseData);
NSData *data = [responseData dataUsingEncoding:NSUTF8StringEncoding];
id json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
NSDictionary *res = [json objectForKey:#"demo"];
NSLog(#"res is %#",res);

Answer 1

I was having a similar problem in one of my projects. I was trying to create NSString from NSData(response from webservice) and i was getting a nil. I found out that using NSASCIIStringEncoding when creating the String solved my problem. It turns out that even though UTF8 has all ASCII chars, char * may not line up correctly for certain characters and by default the init methods do nonlossy encoding which means that nil gets returned when an unexpected char is encountered.
For your case this could be your code.
NSString *responseData = [[NSString alloc] initWithData:_responseData encoding:NSASCIIStringEncoding];
NSLog(#"Data: %#", responseData);
NSData *data = [responseData dataUsingEncoding:NSASCIIStringEncoding];
id json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
NSDictionary *res = [json objectForKey:#"demo"];
NSLog(#"res is %#",res);
NOTE: I am not sure why you are doing all the _responseData->data conversion. If you are doing that just to deserialize your _responseData to json object, you could use it directly in NSJSONSerialization. As below.
id json = [NSJSONSerialization JSONObjectWithData:_responseData options:0 error:nil];
For more information check out this link.

Answer 2

Maybe error appear because you using different encoding? Try using NSUTF8StringEncoding in NSString and in NSData.

Answer 3

From NSString class reference:
-initWithData:encoding:
Return Value
An NSString object initialized by converting the bytes in data into Unicode characters using encoding. The returned
object may be different from the original receiver. Returns nil if the
initialization fails for some reason (for example if data does not
represent valid data for encoding).
Where are you getting _responseData from? Is it definitely an NSDataobject?
Are you sure that you are using the correct encoding?
Could you print out _responseData and update your question so we can take a look?