I\'ve currently implemented a simple selection box using mouse events and redrawing a rectangle on mouse drag. Here\'s my code:
-(void)drawRect:(NSRect)dirty
This post is a little older but I still found no good solution (Framework) on the web. But I guess this is a task (content selection) everyone have to master someday and there is no API from Apple for it. However I made my own framework it and put on Github: https://github.com/ckteebe/MultiSelectionSuiteFramework.