prepareContent(in:)
Prepares the overdraw region for drawing.
Declaration
func prepareContent(in rect: NSRect)Parameters
- rect:
The current overdraw region, specified in the view’s coordinate system. This rectangle includes the view’s visible rectangle plus any space surrounding the visible rectangle that represents the overdraw region.
Discussion
During responsive scrolling, AppKit calls this method before asking your view to draw any content in the overdraw region. You can override this method in your own views and use it to prepare the content that is about to be drawn. For example, if your app defers the creation of subviews until they are scrolled into view, you would use this method to create them and add them to your view hierarchy.
Your implementation of this method must call super at some point. When calling super, you can extend the overdraw rectangle by passing a different rectangle for the rect parameter. For example, if you add a subview whose frame falls outside the current rectangle, you can grow the rectangle to include the entire frame of the subview.
AppKit may call this method multiple times to build up the current overdraw region slowly. Each time it calls the method, it extends the overdraw rectangle passed in the rect parameter. If you pass the same rectangle to super twice in succession, AppKit stops generating additional overdraw content. You can use this behavior to avoid generating more overdraw content than makes sense for your app. If the user scrolls the content, AppKit resets the current overdraw region and starts asking your app for content again. You can also reset the current overdraw region by assigning a value to the preparedContentRect property.