Question

I have an interesting scenario and need to know if it can even be done in Cocoa.

I have tried and failed to find a hourly weather forecast api that is free and will let me see hour-by-hour forecast for a certain city/zipcode. So for an alternate approach what I am trying to do is to read the whole HTML page source and try to see if I can strip out the hourly weather portion so that I can use it in my iPhone app.

NSString *request = @"http://www.findlocalweather.com/hourly/il/chicago.html";

    NSURL *URL = [NSURL URLWithString:request];
    NSError *error;    
    NSString *HTML = [NSString stringWithContentsOfURL:URL encoding:NSASCIIStringEncoding error:&error];

    NSLog(@"HTML: %@", HTML);

If you go to the http://www.findlocalweather.com/hourly/il/chicago.html link you will see the grid hourly forecast. What I need to do is from that HTML source I need to read each date, clouds and temp lines and put that into arrays. e.g.

NSMutableArray1 will contain objects “AUG 05 9:00 AM, AUG 05 10:00 AM, AUG 05 11:00 AM …”

NSMutableArray2 will contain objects “Mostly Cloudy, Mostly Sunny …”

NSMutableArray3 will contain objects “73, 84, 76, 91 ….” (temp in degrees)

Can this be done? Anyone ever tried parsing a HTML page source string to get what you want out of it?

Answer 1

You could do it easily with NSRegularExpression

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:EnterStringWithPatternHere options:0 error:NULL];
NSArray *matches = [regex matchesInString:webPage options:0 range:NSMakeRange(0, [webPage length])];

There are some nice tutorials how to use Regular Expressions (They are almost the same in most programming languages, but look after the specialties of NSRegEx)

Example: Parsing pdf links out of HMTL file.

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"href=\"([^<>]*).pdf\"" options:0 error:NULL];
NSArray *matches = [regex matchesInString:webPage options:0 range:NSMakeRange(0, [webPage length])];
for (int i=0; i<[matches count]; i++) {
    NSTextCheckingResult *match = [matches objectAtIndex:i];
 NSString *theFullString = [NSString stringWithFormat:@"%@.pdf",[webPage   substringWithRange:[match rangeAtIndex:1]]];}

I wrote this code a while ago. I would advise you experiment a bit and make use of NSLog or Breakpoints. This will help a lot. It takes some time to get into the RegEx Stuff but it works very good.