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Either immediately capture the return using a synchronous response, or set up a delegate to receive the data as it comes, as defined in the NSURLConnection class reference. Parse the NSData you receive as you see fit.
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For a simple synchronous response, listing 20.7 shows how to put these elements together.
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Listing 20.7 A simple POSTing example
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NSURL *myURL = [NSURL URLWithString:@"http://www.example.com"]; NSMutableURLRequest *myRequest = [NSMutableURLRequest requestWithURL:myURL]; [myRequest setValue:@"text/xml" forHTTPHeaderField:@"Content-type"]; [myRequest setHTTPMethod:@"POST"]; [myRequest setHTTPBody:myData]; NSURLResponse *response; NSError *error; NSData *myReturn = [NSURLConnection sendSynchronousRequest:myRequest returningResponse:&response error:&error];
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A large number of steps are required to move from the URL through to the data acquisition, just as there were when creating a URL for a simple UIWebView, but once you have them down, the process is pretty easy. The hardest part, as it turns out, is often getting the data ready to POST. This code will work fine for posting plain data to a web page. For example, you could use it with the Google Spell API found at http://www.google.com/tbproxy/spell to send XML data and then read the results with NSXMLParser. Things can get pretty tricky if you re doing more intricate work than that, such as POSTing form data.
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20.6.2 Submitting forms
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Sending form data to a web page follows the same process as any other POSTed data, and reading the results works the same way. The only tricky element is packaging up the form data so that it s ready to use. The easiest way to work with form data is to create it using an NSDictionary or NSMutableDictionary of keys and values, because that matches the underlying structure of HTML forms. When you re ready to process the data, you pass the dictionary to a method that turns it into NSData, which can be sent as an NSMutableURLRequest body. Once you ve written this method the first time, you can use it again and again. Listing 20.8 shows how to turn a dictionary of NSStrings into NSData.
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Listing 20.8 Creating form data
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- (NSData*)createFormData:(NSDictionary*)myDictionary withBoundary:(NSString *)myBounds { NSMutableData *myReturn = [[NSMutableData alloc] initWithCapacity:10];
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The web: web views and internet protocols
NSArray *formKeys = [dict allKeys]; for (int i = 0; i < [formKeys count]; i++) { [myReturn appendData: [[NSString stringWithFormat:@"--%@\n",myBounds] dataUsingEncoding:NSASCIIStringEncoding]]; [myReturn appendData: [[NSString stringWithFormat: @"Content-Disposition: form-data; name=\"%@\"\n\n%@\n", [formKeys objectAtIndex:i], [myDictionary valueForKey:[formKeys objectAtIndex: i]]] dataUsingEncoding:NSASCIIStringEncoding]]; } [myReturn appendData: [[NSString stringWithFormat:@"--%@--\n", myBounds] dataUsingEncoding:NSASCIIStringEncoding]]; return myReturn; }
There s nothing particularly notable here. If you have a sufficiently good understanding of the HTML protocol, you can easily dump the dictionary elements into an NSData object. The middle appendData: method is the most important one, because it adds both the key (saved in an NSArray) and the value (available in the original NSDictionary) to the HTML body. Back outside the method, you can add the data to your NSMutableURLRequest just as in listing 20.7, except the content type will look a little different:
NSMutableURLRequest *myRequest = [NSMutableURLRequest requestWithURL:myURL]; NSString *myContent = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",myBounds] [myRequest setValue:myContent forHTTPHeaderField:@"Content-type"]; [myRequest setHTTPMethod:@"POST"]; [myRequest setHTTPBody:myReturn];
Some other types of data processing, such as file uploads, will require somewhat different setups, and you d do well to look at HTML documentation for the specifics, but the general methods used to POST data will remain the same. With POSTing out of the way, we ve now covered all of the SDK s most important functions related to the internet. But there s one other topic that we want to touch upon before we close this chapter a variety of internet protocols that you can access through third-party libraries.
20.7 Accessing the social web
Since the advent of web 2.0, a new sort of internet presence has appeared. We call it the social web. This is an interconnected network of web servers that exchange information based on various well-known protocols. If you re building internet-driven programs, you may wish to connect up to this web so that your iPhone users can become a part of it.
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