UITableView and NXXMLParser ... Calling Heirarchy

Question

Hi Guys,

I am stuck in a strange situation , i am getting data from the website using XML files and i am filling an Array (NSMutableArray Type) that i later use to display the data on Table View. The problem is that functions related to UITableView are called earlier and at that time the Array is not filled, this cause the program to crash. When this function is executed arrayData is empty and count functions returns nothing. Is there any way that i call NSXMLParser functions earlier than the UITableView functions.

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section 
{
    return [arrayData count];
}

Thanks, Taimur

Answer 1

The array would return 0 if it existed but without containing any objects - so the app shouldn't crash. This means your array has not been initialized yet. You have propably added a pointer to your array as an instance variable and maybe as property, but you still need to create the actual object towards which that pointer should point.

So, if we're dealing with a property of a viewcontroller subclass here, add something like this to your viewDidLoad method:

NSMutableArray *newArray = [[NSMutableArray alloc] init];
self.arrayData = newArray;
[newArray release];

Answer 2

Your situation is not strange at all - it is extremely common when developing apps with asynchronous data loading requirements.

NSXMLParser is a SAX (event-driven) parser - it will parse data when the data is available. It is up to you when you choose to display your table, but obviously if you try to display it before the XML data is available then you will have to take steps to prevent a crash, or at the very least a bad user experience. Typically you would display an activity spinner or a "loading data..." message until the data is ready, and in a background thread load the XML. Once loaded, the BG thread should signal to the UI thread that the data is ready, and perhaps invoke reloadData on the table to load the data.