Styling NSOutlineView Rows

Question

I have a Document based Core Data app with an NSTreeController supplying the content to a view based NSOutlineView. I am "styling" (setting text colour, background colour etc.) the rows based on persistent "transformable" NSColor and NSFont attributes in my data model which the end use can modify. When a new row is popped up, it displays things with the colours/fonts set in the data model. Here is the delegate/datasource code that sets the row background colour:

- (void) outlineView:(NSOutlineView *)outlineView
       didAddRowView:(NSTableRowView *)rowView
              forRow:(NSInteger)row
{
    // Get the relevant nodeType which contains the attributes
    QVItem *aNode = [[outlineView itemAtRow:row] representedObject];
    if (aNode.backColor)
    {
        rowView.backgroundColor = aNode.backColor;
    }
}

However when the style attributes change I want the associated visible rows to be redrawn with the new style values. Each time a "style" attribute is changed, I am using NSNotificationCenter to send a notification to the Outline view delegate, with the model object whose row needs to be redrawn with the changed style. This is the code in the delegate that receives the notification.

-(void) styleHasChanged: (NSNotification *)aNotification
{
    NSTreeNode *aTreeNode = [myTreeController treeNodeForModelObject:aNotification.object];
    [myOutlineView reloadItem:aTreeNode];
}

My assumption here is that I can navigate the tree controller to find the tree node which is representing my model object and then ask the outline view to redraw the row for that tree node. This is the "additions" code in the tree controller which walks the tree to find the object - not super efficient, but I don't think there is another way.

@implementation NSTreeController (QVAdditions)

- (NSTreeNode *)treeNodeForModelObject:(id)aModelObject
{
    return [self treeNodeForModelObject:aModelObject inNodes:[[self arrangedObjects] childNodes]];
}

- (NSTreeNode *)treeNodeForModelObject:(id)aModelObject inNodes:(NSArray*)nodes
{
    for(NSTreeNode* node in nodes)
    {
        if([node representedObject] == aModelObject)
            return node;
        if([[node childNodes] count])
        {
            NSTreeNode * treeNode = [self treeNodeForModelObject:aModelObject inNodes:[node childNodes]];
            return treeNode;
        }
    }
    return nil;
}

So sometimes this works and the row redraws, and sometimes it doesn't. The delegate method "styleHasChanged:" is always called, and the tree controller always returns a corresponding tree node (Actually of a subclass of NSTreeNode). But more often than not the outline view does not recognise the tree node, and the row is not redrawn. Its like the tree controller has given back a different tree node object to the one it gave the outline view in the past. But weirdly sometimes it does work and the right row is redrawn with the new background colour. If I collapse the row out of view and pop it open again, it is redrawn correctly.

Anyone any idea why it works sometimes and not other times?

It would be nice to be able to bind the colour/font attributes to the row and columns in some way, so that the outline view did this styling automatically with KVO, but I don't think that is possible - is it?

Answer 1

You spend hours/days trying to work out what you've done wrong; You write the question out; Post it; Sleep on it; and think how stupid can you be.

So I asked the NSTableRowView to redraw itself, but I had not set the new background colour. So here is the new improved (and works) version of styleHasChanged:

-(void) styleHasChanged: (NSNotification *)aNotification
{
    QVItem *modelItem = aNotification.object;
    NSTreeNode *aTreeNode = [myTreeController treeNodeForModelObject:modelItem];
    NSInteger rowIndex = [myOutlineView rowForItem:aTreeNode];
    if !(rowIndex == -1)
    {
        NSTableRowView *rowViewToBeUpdated = [myOutlineView rowViewAtRow:rowIndex makeIfNecessary:YES];
        rowViewToBeUpdated.backgroundColor = modelItem.backColor;
    }
}

Duh!