Yahoo weather API using NSXMLParser [closed]

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This is the documentation provided by Yahoo: http://developer.yahoo.com/weather/

At the moment this is my code:

NSString *location =  @"Palermo";
NSString *temperatureUnit = @"c";
NSString *address = @"http://weather.yahooapis.com/forecastrss?w=";
NSString *request = [NSString stringWithFormat:@"%@%@&u=%@",address,location, temperatureUnit];
NSURL * URL = [NSURL URLWithString:request];
NSXMLParser * doc = [[NSXMLParser alloc] initWithContentsOfURL:URL];

I'd like to know how to get the temperature value using NSXMLParser

Answer 1

You create your parser, but you don't parse. Let's assume you created your parser like so:

NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:URL];

You then need to set the delegate and initiate the parse:

parser.delegate = self;
[parser parse];

You then have to write your NSXMLParserDelegate methods. (For more information on NSXMLParser, see the Event-Driven XML Programming Guide.) E.g., if you only need temperature, you could write a didStartElement method:

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
{
    if ([elementName isEqualToString:@"yweather:condition"])
    {
        // do whatever you want with `attributeDict`, perhaps saving it in some class property; I'm just going to log it

        NSLog(@"current condition = %@", attributeDict); 
    }           
}

Note, the city should be a WOEID. (See the API description.) So, instead of a location of:

NSString *location =  @"Palermo";

You should use (for Palermo in Italy):

NSString *location =  @"719846";

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By the way, I agree with Caleb that you should either do this initWithContentsOfURL in a background queue, or you should otherwise retrieve the NSData using some asynchronous mechanism.

For example, you could do:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSString *location = @"719846";
    NSString *temperatureUnit = @"c";
    NSString *address = @"http://weather.yahooapis.com/forecastrss?w=";
    NSString *request = [NSString stringWithFormat:@"%@%@&u=%@",address,location, temperatureUnit];
    NSURL *URL = [NSURL URLWithString:request];

    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:URL];
    parser.delegate = self;
    [parser parse];
});

If you do this in the background queue, make sure to dispatch UI updates back to the main queue, e.g.:

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
{
    if ([elementName isEqualToString:@"yweather:condition"])
    {
        // UI updates should be dispatched back to the main queue, e.g.:
        dispatch_async(dispatch_get_main_queue(), ^{
            NSString *temp = attributeDict[@"temp"];
            self.tempLabel.text = temp;
        });
    }
}

Answer 2

You'll need to create an URL request from that URL, make the request withNSURLConnection, and receive the response. There are a number of good examples in Apple's documentation, so no need to repeat them here. Or, you can use initWithContentsOfURL: as you're doing above, but don't do that in the main thread as it'll cause your app to freeze until the response is received; if the server takes too long to respond, iOS will kill your app. Once you have the response, you'll parse it with the XML parser -- you'll need to create a delegate so that the parser can hand you the data as it encounters it during parsing.