Federico Zancan Federico Zancan - 1 month ago 8
Objective-C Question

iOS: how to perform a HTTP POST request?

I'm approaching iOS development and I'd like to have one of my first applications to perform a HTTP POST request.

As far as I can understand, I should manage the connection which handles the request via a

NSURLConnection
object, which forces me to have a delegate object, which in turn will handle data events.

Could someone please clarify the task with a practical example?

I should contact an https endpoint sending authentication data (username and password) and getting back a plain text response.

Answer

You can use NSURLConnection as follows:

  1. Set your NSURLRequest: Use requestWithURL:(NSURL *)theURL to initialise the request.

    If you need to specify a POST request and/or HTTP headers, use NSMutableURLRequest with

    • (void)setHTTPMethod:(NSString *)method
    • (void)setHTTPBody:(NSData *)data
    • (void)setValue:(NSString *)value forHTTPHeaderField:(NSString *)field
  2. Send your request in 2 ways using NSURLConnection:

    • Synchronously: (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error

      This returns a NSData variable that you can process.

      IMPORTANT: Remember to kick off the synchronous request in a separate thread to avoid blocking the UI.

    • Asynchronously: (void)start

Don't forget to set your NSURLConnection's delegate to handle the connection as follows:

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    [self.data setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)d {
    [self.data appendData:d];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    [[[[UIAlertView alloc] initWithTitle:NSLocalizedString(@"Error", @"")
                                 message:[error localizedDescription]
                                delegate:nil
                       cancelButtonTitle:NSLocalizedString(@"OK", @"") 
                       otherButtonTitles:nil] autorelease] show];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSString *responseText = [[NSString alloc] initWithData:self.data encoding:NSUTF8StringEncoding];

    // Do anything you want with it 

    [responseText release];
}

// Handle basic authentication challenge if needed
- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
    NSString *username = @"username";
    NSString *password = @"password";

    NSURLCredential *credential = [NSURLCredential credentialWithUser:username
                                                             password:password
                                                          persistence:NSURLCredentialPersistenceForSession];
    [[challenge sender] useCredential:credential forAuthenticationChallenge:challenge];
}
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