Hi,
I'm running X-Code 3.1.3 on OS X 10.5.7, Intel Macbook. As a means of
getting the hang of Cocoa, and having some fun at the same time, I've
been building a simple Desktop Twitter Client.
I've previously worked through Hillegass' excellent Cocoa book.
Building on his example of using Amazon XML Data, I've managed to
download the status update XML from Twitter and have it displaying in
an NSTableView, using my AppController class to parse the XML as a
data source. This works a treat, but as different Tweets are of
different lengths, I wanted to implement variable row heights.
I've made my AppController class a delegate of the NSTableView (it is
also acting as the Data Source), and implemented the
tableView:heightOfRow: delegate method as follows:
- (CGFloat)tableView:(NSTableView *)tv heightOfRow:(NSInteger)row
{
// Get second column (index 1 - status text)
// (first column, index 0, is Twitter profile pic)
NSTableColumn *column = [[tv tableColumns] objectAtIndex:1];
// Get text cell from second column for row
NSCell *cell = [column dataCellForRow:row];
// Calculate height using cellSizeForBounds, limiting it to width of
column.
// Adding 10 pixels for padding.
float height = [cell cellSizeForBounds:
NSMakeRect(0.0, 0.0, [column
width], 1000.0)].height+10.0;
// Profile pics are 48x48, so ensure size is at least 58px to allow
some padding
height = MAX(height,58.0);
return height;
}
Note that I've already set Wrap etc in Interface Builder. This works,
but suffers from a fair amount of graphical corruption. Each row
appears to draw itself with the correct height, but if one row is
particularly tall the next row down is prone to overlap slightly, as
if it's origin is not being updated by the increased height of the
previous row. This results in text collision.
Best illustrated with a picture: http://twitpic.com/9fzeq
The issue here is not that the row height is too low - if I set
tableView:heightOfRow: to return a constant, deliberately too low
value (48.0 in this example), then the cell contents are simply
truncated and no text collision occurs.
Picture of this: http://twitpic.com/9fzqy
Further experimentation with tableView:heightOfRow: shows that
provided the value returned is constant, it has no problem tiling the
rows, but if the value varies (I wrote a toy program randomly
generating row heights in the range 48..80), then this kind of
collision occurs. Given as the whole point in this method is to
support differing row heights, I find this a bit odd.
So, am I doing something obviously wrong, or is this a problem with
Cocoa itself?
Cheers in advance,
Alex
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