NSOutlineView rowForItem: always returns 0

Question

I have an app which needs to update cells in certain columns asynchronously. I have a GCD queue which blocks are added to which later gets the cell for the row and column given using -rowForItem: but the result of -rowForItem: is consistently 0, and NSAssert([self.outlineView itemAtRow:row] == item, @"rowForItem: and itemForRow: not reversible! (Item %@, row %ld)", item, (long)row); throws every time. I don't see what I'm doing wrong here. The index is not -1, which means that the item wasn't found, but the item is said to be at the incorrect index. (The first item is always a JODirectoryInfo, and I only run the block on JOFileInfo, so it can't be the wrong item.)

- (NSTableCellView *)_cellForRow:(NSInteger)row columnIdentifier:(NSString *)column {
    if (row < 0) return nil;
    NSInteger colIdx = [self.outlineView columnWithIdentifier:column];
    if (colIdx == -1) return nil;
    if (colIdx + 1 > self.outlineView.tableColumns.count) return nil;
    return [self.outlineView viewAtColumn:colIdx row:row makeIfNecessary:NO];
}
- (NSTableCellView *)_cellForItem:(id)item columnIdentifier:(NSString *)column {
    NSInteger row = [self.outlineView rowForItem:item];
    NSAssert([self.outlineView itemAtRow:row] == item, @"rowForItem: and itemForRow: not reversible! (Item %@, row %ld)", item, (long)row);
    DDLogVerbose(@"Getting cell for item %@ (row %ld) in column %@", item, (long)row, column);
    return [self _cellForRow:row columnIdentifier:column];
}

- (dispatch_block_t)_loadingBlockForItem:(JOFileInfo *)item block:(JOFileInfoBlock)block column:(NSString *)columnIdentifier {
    return ^{
        NSTableCellView *cellView = [self _cellForItem:item columnIdentifier:columnIdentifier];
        if (!cellView) return;
        cellView.objectValue = block(item);
    };
}
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item {
    DDLogVerbose(@"Requested value of column %@ for item %@", tableColumn.identifier, item);
    if ([tableColumn.identifier isEqualToString:@"Size"]) {
        if ([item isKindOfClass:[JOFileInfo class]]) {
            dispatch_async(self.queue, [self _loadingBlockForItem:item block:^(JOFileInfo *item) {
                unsigned long long size = item.size;
                if (size != ULONG_LONG_MAX) return [self.byteCountFormatter stringFromByteCount:size];
                else return @"--";
            } column:tableColumn.identifier]);
            return @"--";
        } else {
            return @"--";
        }
    } else {
        return @"text";
    }
}

Answer 1

It returned zero because the outline view was nil.