Objective C - POST data using NSURLConnection

Question

I'm very slowly working my way through learning the URL loading system for iOS development, and I am hoping someone could briefly explain the following piece of code:

NSString *myParameters = [[NSString alloc] initWithFormat:@"one=two&three=four"];
[myRequest setHTTPMethod:@"POST"];
[myRequest setHTTPBody:[myParameters dataUsingEncoding:NSUTF8StringEncoding]];

Eventually I would like to be able to create an application that logs into my ISP's website and retrieves how much data I have left for the rest of the month, and I feel as though I should get my head around setHTTPMethod/setHTTPBody first.

Kind regards

Answer 1

This is a pretty simple HTTP request setup; if you have more specific questions you might do better asking those.

NSString *myParameters = @"paramOne=valueOne&paramTwo=valueTwo";

This sets up a string containing the POST parameters.

[myRequest setHTTPMethod:@"POST"];

The request needs to be a POST request.

[myRequest setHTTPBody:[myParameters dataUsingEncoding:NSUTF8StringEncoding]];

This puts the parameters into the post body (they need to be raw data, so we first encode them as UTF-8).

Answer 2

Step 1 : set URL definitions:

// Create the request

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://192.168.0.232:8080/xxxx/api/Login"]];

    // Specify that it will be a POST request
    request.HTTPMethod = @"POST";

    // This is how we set header fields
    [request setValue:@"application/x-www-form-urlencoded; charset=utf-8" forHTTPHeaderField:@"Content-Type"];

    NSMutableDictionary *postDict = [[NSMutableDictionary alloc] init];

    [postDict setValue:@"Login" forKey:@"methodName"];
    [postDict setValue:@"admin" forKey:@"username"];
    [postDict setValue:@"123456" forKey:@"password"];
    [postDict setValue:@"mobile" forKey:@"clientType"];


    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:postDict options:0 error:nil];

    // Checking the format
    NSString *urlString =  [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];


    // Convert your data and set your request's HTTPBody property
    NSString *stringData = [[NSString alloc] initWithFormat:@"jsonRequest=%@", urlString];

    //@"jsonRequest={\"methodName\":\"Login\",\"username\":\"admin\",\"password\":\"12345678n\",\"clientType\":\"web\"}";

    NSData *requestBodyData = [stringData dataUsingEncoding:NSUTF8StringEncoding];

    request.HTTPBody = requestBodyData;

    // Create url connection and fire request
    NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    if (!theConnection) {

        // Release the receivedData object.
        NSMutableData *responseData = nil;

        // Inform the user that the connection failed.
    }

Step 2: 

// Declare the value for NSURLResponse URL

//pragma mark NSURLConnection Delegate Methods

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    // A response has been received, this is where we initialize the instance var you created
    // so that we can append data to it in the didReceiveData method
    // Furthermore, this method is called each time there is a redirect so reinitializing it
    // also serves to clear it
    _responseData = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    // Append the new data to the instance variable you declared
    [_responseData appendData:data];

    NSError *error=nil;

    // Convert JSON Object into Dictionary
    NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:_responseData options:
                          NSJSONReadingMutableContainers error:&error];



    NSLog(@"Response %@",JSON);
}

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection
                  willCacheResponse:(NSCachedURLResponse*)cachedResponse {
    // Return nil to indicate not necessary to store a cached response for this connection
    return nil;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // The request is complete and data has been received
    // You can parse the stuff in your instance variable now

}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    // The request has failed for some reason!
    // Check the error var
}