How to find the key of a `NSTableColumn` to draw the sort indicator?

Question

I created a custom NSTableViewHeader . Everything works fine, but I don't find a simple way to get the "key" for the current column to check if the sort indicator should be drew.

Here the core code to check for the sort indicator:

// Check if we need to draw a sort descriptor
for (NSInteger priority = 0; priority < self.tableView.sortDescriptors.count; ++priority) {
    NSSortDescriptor *sortDesciptor = self.tableView.sortDescriptors[priority];
    if ([sortDesciptor.key isEqualTo:???????]) {
        [tableHeaderCell drawSortIndicatorWithFrame:rect inView:self ascending:sortDesciptor.ascending priority:priority];
    }
}

To see everything in context, here the whole drawRect code:

- (void)drawRect:(NSRect)dirtyRect
{
    [NSGraphicsContext saveGraphicsState];
    // Fill the background
    [_backgroundColor setFill];
    const CGRect headerRect = CGRectMake(0.0, 1.0, self.bounds.size.width, self.bounds.size.height-1.0);
    [[NSBezierPath bezierPathWithRect:headerRect] fill];

    // Draw separators and column header text.
    for (NSUInteger i = 0; i < self.tableView.numberOfColumns; ++i) {
        NSRect rect = [self headerRectOfColumn:i];
        if (i != 0) {
            [[NSColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.35] setFill];
            [[NSBezierPath bezierPathWithRect:NSMakeRect(rect.origin.x, rect.origin.y+4.0, 1.0, rect.size.height-8.0)] fill];
        }
        NSTableColumn *tableColumn = self.tableView.tableColumns[i];
        NSTableHeaderCell *tableHeaderCell = tableColumn.headerCell;
        NSString *columnText = tableHeaderCell.stringValue;
        [columnText drawInRect:NSInsetRect(rect, 5.0, 4.0) withAttributes:_headerTextAttributes];

        // Check if we need to draw a sort indicator
        for (NSInteger priority = 0; priority < self.tableView.sortDescriptors.count; ++priority) {
            NSSortDescriptor *sortDesciptor = self.tableView.sortDescriptors[priority];
            if ([sortDesciptor.key isEqualTo:tableColumn.key]) {
                [tableHeaderCell drawSortIndicatorWithFrame:rect inView:self ascending:sortDesciptor.ascending priority:priority];
            }
        }
    }
    [NSGraphicsContext restoreGraphicsState];
}

How can I find the "key" for the current column to check if the sort indicator shall be drew?

Answer 1

The only way which worked for me is checking the bindings of the NSTableColumn . This is working for me, because I use a NSArrayController . My NSTableView is using a cell based layout and each NSTableColumn is bound to the arrangedObjects.xxx key path.

// Check if we need to draw a sort descriptor
for (NSInteger priority = 0; priority < self.tableView.sortDescriptors.count; ++priority) {
    NSSortDescriptor *sortDesciptor = self.tableView.sortDescriptors[priority];
    NSDictionary *bindingInfo = [tableColumn infoForBinding:@"value"];
    NSString *keyPath = bindingInfo[NSObservedKeyPathKey];
    keyPath = [keyPath stringByReplacingOccurrencesOfString:@"arrangedObjects." withString:@""];
    if ([sortDesciptor.key isEqualTo:keyPath]) {
        [tableHeaderCell drawSortIndicatorWithFrame:rect inView:self ascending:sortDesciptor.ascending priority:priority];
    }
}

But this won't work for view based tables. Is this really the only solution?