Connecting to a RESTful webservice in objective-c - objective-c

Question

I tried connecting to a web service and retrieve data from it, but I did not succeed in doing so. Here is what I have done.
This is the web service I'm trying to connect to http://www.rcsb.org/pdb/software/rest.do
Here is my example.h file:
#import <Foundation/Foundation.h>
#interface example : NSObject {
NSMutableData *receivedData;
}
#property(nonatomic, retain) NSMutableData *receivedData;
- (void) getDataFromServer;
#end
Here is my example.m file:
import "example.h"
#implementation example
#synthesize receivedData;
-(void) getDataFromServer {
//prepare request
NSString *urlString = [NSString stringWithFormat:#"http://www.rcsb.org/pdb/rest/search/"];
NSMutableURLRequest *theRequest = [[NSMutableURLRequest alloc] init];
[theRequest setURL:[NSURL URLWithString:urlString]];
[theRequest setHTTPMethod:#"POST"];
NSString *myXmlQuery = [[NSString alloc] initWithFormat:#"<?xml version=\"1.0\" encoding=\"UTF-8\"?><orgPdbQuery><version>head</version><queryType>org.pdb.query.simple.AdvancedKeywordQuery</queryType><description>Text Search for: chloro</description><keywords>chloro</keywords></orgPdbQuery>"];
//set Headers
NSString *contentType = [NSString stringWithFormat:#"application/xml"];
[theRequest addValue:contentType forHTTPHeaderField:#"Content-Type"];
[theRequest addValue:[NSString stringWithFormat:#"%ld", [myXmlQuery length]] forHTTPHeaderField:#"Content-Length"];
//create the Body
NSMutableData *postBody = [NSMutableData data];
[postBody appendData:[[NSString stringWithFormat:#"<xml>"] dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[myXmlQuery dataUsingEncoding:NSUTF8StringEncoding]];
[postBody appendData:[[NSString stringWithFormat:#"</xml>"] dataUsingEncoding:NSUTF8StringEncoding]];
//post
[theRequest setHTTPBody:postBody];
NSLog(#"%#", myXmlQuery);
//get response
NSHTTPURLResponse *urlResponse = [[NSHTTPURLResponse alloc] init];
NSError *error = [[NSError alloc] init];
NSData *responseData = [NSURLConnection sendSynchronousRequest:theRequest returningResponse:&urlResponse error:&error];
NSString *result = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
NSLog(#"Response code- %ld",[urlResponse statusCode]);
NSLog(#"Response: %#", result);
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSLog(#"in didReceiveResponse....setting receivedData to zero");
//[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
NSLog(#"In didReceiveData...receiving data and appending to receivedData");
[receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog(#"Connection failed with error");
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(#"in connectionDidFinishLoading");
NSLog(#"Succeeded! Received %ld bytes of data", [receivedData length]);
}
#end
I'm getting a html page as a response to this. Moreover, connectionDidFinishLoading is not being invoked any time because I'm not getting the NSLog statements in my output. All I am getting is the html version of the url I'm trying to connect to.
Any kind of help will be appreciated. Thank you.
PS: I'm trying to format this text properly but it is automatically getting formatted like this. Sorry for the inconvenience.

Answer 1

It looks like you are trying to do two different things. Firstly, I suggest you look at the URL Loading System Programming Guide. You also do not need to create a NSHTTPURLResponse* as that gets taken care of for you.
Secondly, you are trying to use the NSURLConnectionDelegate protocol without conforming to it, or adding your class as a delegate. This differs greatly from doing sendSynchronousRequest which will block the main thread, and does not need the delegate set because that method will wait for a response and not allow any other code to execute (hence blocking the thread). There's a really nice StackOverflow question and answer very similar to yours.
In a nutshell:
Conform to <NSURLConnectionDelegate> in your interface.
Create a property for a NSURLConnection*
Use self.myConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
Now you can rely on the NSURLConnectionDelegate protocol methods being called (connectionDidFinishLoading:, connection:didReceiveData:, etc).
Once you hit connectionDidFinishLoading: you can start using the data you downloaded.