Now that we have examined the XML file in a web browser, we need to download it into our App and parse it to extract the information that we need. Specifically, we are looking for the following:
The last update time
The list of currency codes and exchange rates
By looking at the XML Tree, and noting the position of the disclosure triangles, we can determine the paths to the information that we want to access. It becomes clear that the path to the last update time is as follows:
/gesmes:Envelope/Cube/Cube
And the path to the exchange rates is as follows:
/gesmes:Envelope/Cube/Cube/Cube
When we extract the exchange rate information we are going to save it in something called an NSDictionary. Actually we will use the mutable variant, NSMutableDictionary, since we want to modify the object instance.
A dictionary is an object that allows us to use one object as a key and a second object as a value that corresponds to that key (this is called a key->value pair).
In this instance...