Question

I’m having trouble fully understanding all the different places you can return cells when using an OutlineView. As far as I can tell there are four places:

NSOutlineViewDataSource has:

• outlineView:child
• outlineView:objectValueForDataColumn

And NSOutlineViewDelegate has:

• outlineView:willDisplayCell
• outlineView:dataCellForTableColumn

If I have a outline view with different items, like the SourceList example, where do I do what and why? I have GroupItem headers and a tree of IconAndImage cells that subclass NSTextFieldCell. Where should these be instantiated and where should I set the styling, image and title?

Answer 1

What Cocoa means by the word cell is not the same as what you would call a cell in for example Excel.

In Cocoa, a cell is a NSCell subclass and could be considered as a light-weight reusable NSView. It is used to draw many items in the same way. E.g.

- (void)drawRect:(NSRect)draw_rect {
    // ...
    for ( id value in myDataArray ) {
        [cell setObjectValue:value];
        NSRect cellFrame = ...;
        [cell drawWithFrame:cellFrame inView:self];
    }

So a data source does not return cells, but instead return objects that are parameters to [(NSCell) -(void)setObjectValue:(id)value]. The delegate returns which cell-object to use for each item and should be implemented so that you only create each cell-type once. E.g.

- (NSCell *)outlineView:(NSOutlineView *)outlineView
 dataCellForTableColumn:(NSTableColumn *)tableColumn
                   item:(id)item {
    NSCell *cell = nil;
    switch(tableColumn.tag) {
         case 0:
             if  ( ! myCell ) {
                  myCell = [[NSCell alloc] init];
             }
             cell = myCell;
             break;
        default:
             break;
    }
    return cell;
}

You should use table column tags or a similar feature to handle column re-ordering by the user.