NSTableView's viewForTableColumn:row: called for more rows than expected in Mavericks

Question

My understanding was that viewForTableColumn:row: would be called only for rows that are visible.

I confirmed this using the following: NSRange rowsInRect = [aTableView rowsInRect:[aTableView visibleRect]]; NSInteger lastVisibleRow = rowsInRect.location + rowsInRect.length;

But with Mavericks, viewForTableColumn:row is getting called many more times without scrolling down.

For example, if my last visible row was 35, data source method is called for 139 rows.

Can anybody explain this?

Answer 1

I found the explanation to this in AppKit Release notes for OS X v10.9.

Here goes:

Mac OS 10.9 has a new feature called Responsive Scrolling. Responsive Scrolling allows the application to continue to rapidly scroll content even when the application’s main thread is busy doing other work. AppKit accomplishes this by having the document view draw more than what is currently visible during idle.

To facilitate Responsive Scrolling, your document view will be asked to draw portions that are not currently visible to the user.

The following method is called by NSView with a 'rect' for a recommended area that should be fully rendered for overdraw. Override this method and bring in additional subviews and pre-cached content for the 'rect' in order to perform responsive scrolling. To suppress overdraw for a particular view (such as NSTableView), override this method and call [super prepareContentInRect:[self visibleRect]].

(void)prepareContentInRect:(NSRect)rect;