OutlineViewrowViewForItem

OutlineViewrowViewForItem refers to the delegate method of the NSOutlineView class in macOS AppKit, formally named outlineView:rowViewForItem:. This method allows a developer to provide a custom NSTableRowView instance for a particular item in the outline view, enabling custom visual styling or interactive elements within individual rows.

When an NSOutlineView needs to display a row it calls the delegate and passes the table view instance and the item whose row is being displayed. The delegate method returns an NSTableRowView object. If the delegate returns nil, the outline view instantiates a default NSTableRowView, which is a simple, unmodified row view. Returning a custom subclass lets the developer modify background colors, show selection indicators, or embed graphics.

Typical use cases include highlighting rows based on data conditions, adding per-row controls such as checkboxes or buttons, or integrating third‑party row view customizations. The method is called lazily, so it can be used to defer row view allocation until a row is about to appear on screen, aiding performance for large data sets.

An example signature in Objective‑C is:

- (NSTableRowView )outlineView:(NSOutlineView )outlineView rowViewForItem:(id)item;

In Swift it is:

func outlineView(_ outlineView: NSOutlineView, rowViewForItem item: Any) -> NSTableRowView?

To implement proper reuse, the custom row view should be efficiently configured each time the method is called, as rows are reused when scrolling. The delegate can also use outlineView:isRowExpandable: or outlineView:viewForTableColumn:row: to further customize cell contents. The outlineView:rowViewForItem: method was introduced to provide granular control over row presentation beyond what the default row view offers.