Open Radar

 
Summary:

I noticed that in my app the UITableView when it initialises requests info about all of the sections in the data source, even if they will not yet be displayed. This can cause a huge amount of unnecessary data lookups.

What's more, the problems seems to be an unintended side effect of updating the section count on the UITableView.

Steps to Reproduce:

1) Create an app with UITableView
2) Add a table view delegate
3) Implement - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section 
4) Add a breakpoint in the implementation of tableView:titleForHeaderInSection
5) Implement - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView to return a non-zero number, say 25
6) Run the app and see tableView:titleForHeaderInSection called 25 times as the view is about to be presented

Expected Results:

tableView:titleForHeaderInSection should only be called for the sections that will be visible on the initial screen. 

Actual Results:

tableView:titleForHeaderInSection is called once for every section declared in numberOfSectionsInTableView, causing potentially huge amounts of unnecessary data retrieval.

Regression:

Not sure.

Notes:

I'm attaching a screen grab of the call stack showing what causes the tableView:titleForHeaderInSection to be called in this scenario. It looks like a side effect of [UITableViewRowData numberOfRows.]