TimeLine view - rollovers

Each row of the TimeLine header view has two areas that are active. One is the drawMode and has a popup - the other represents the locked status of an item. These appear as graphics in the TimeLine header. I have decided to make these active areas distinct by making them behave as rollovers. The effect that I am looking for is quite simple - as the mouse goes over the active area I want to draw a grey oval. This will also provide an opportunity to draw a popup arrow for the popup. Adding the arrow so that it always draws makes the header look cluttered - only drawing this in the mouse-over state will make this a little cleaner.

The simplest way I found to do this is to use the NSTrackingArea. My aim was to add a NSTrackingArea for each visible active area.

To do this I added an updateTrackingAreas method to the view - in here I dispose of any existing tracking areas, and then to loop through all of the visible rows and for each to add a tracking area for each of the active areas on the row. When you construct a tracking area you pass in a NSDictionary of userInfo - here I pass in details of the row and the particular active area it represents. The updateTrackingAreas method is called when the header view scrolls or is resized - for the moment this is enough.

When you establish tracking areas on a view mouseEntered and mouseExited methods of your view will be called as the mouse enters and exits the view. here you need to get the relevant areas to redraw - I affected a method setNeedsDisplayInRow that is little more that a sprinkle of sugar for setNeedsDisplayInRect.

My guess is that the procedure for getting a rollover to work for a cell in in an NSTableView would be pretty much the same - though you might need to updateTrackingAreas in more situations (for example when table rows are resized).

Currently the drawing is still handled by the header view - but I plan to move this into a NSCell subclass.

An active area with a rollover.