objective c - View-based NSTableView with rows that have dynamic heights

Question

I have an application with a view-based NSTableView in it. Inside this table view, I have rows that have cells that have content consisting of a multi-row NSTextField with word-wrap enabled. Depending on the textual content of the NSTextField, the size of the rows needed to display the cell will vary.

I know that I can implement the NSTableViewDelegate method -tableView:heightOfRow: to return the height, but the height will be determined based on the word wrapping used on the NSTextField. The word wrapping of the NSTextField is similarly based on how wide the NSTextField is… which is determined by the width of the NSTableView.

Soooo… I guess my question is… what is a good design pattern for this? It seems like everything I try winds up being a convoluted mess. Since the TableView requires knowledge of the height of the cells to lay them out... and the NSTextField needs knowledge of it's layout to determine the word wrap… and the cell needs knowledge of the word wrap to determine it's height… it's a circular mess… and it's driving me insane.

Suggestions?

If it matters, the end result will also have editable NSTextFields that will resize to adjust to the text within them. I already have this working on the view level, but the tableview does not yet adjust the heights of the cells. I figure once I get the height issue worked out, I'll use the -noteHeightOfRowsWithIndexesChanged method to inform the table view the height changed… but it's still then going to ask the delegate for the height… hence, my quandry.

Thanks in advance!

Answer 1

This is a chicken and the egg problem. The table needs to know the row height because that determines where a given view will lie. But you want a view to already be around so you can use it to figure out the row height. So, which comes first?

The answer is to keep an extra NSTableCellView (or whatever view you are using as your "cell view") around just for measuring the height of the view. In the tableView:heightOfRow: delegate method, access your model for 'row' and set the objectValue on NSTableCellView. Then set the view's width to be your table's width, and (however you want to do it) figure out the required height for that view. Return that value.

Don't call noteHeightOfRowsWithIndexesChanged: from in the delegate method tableView:heightOfRow: or viewForTableColumn:row: ! That is bad, and will cause mega-trouble.

To dynamically update the height, then what you should do is respond to the text changing (via the target/action) and recalculate your computed height of that view. Now, don't dynamically change the NSTableCellView's height (or whatever view you are using as your "cell view"). The table must control that view's frame, and you will be fighting the tableview if you try to set it. Instead, in your target/action for the text field where you computed the height, call noteHeightOfRowsWithIndexesChanged:, which will let the table resize that individual row. Assuming you have your autoresizing mask setup right on subviews (i.e.: subviews of the NSTableCellView), things should resize fine! If not, first work on the resizing mask of the subviews to get things right with variable row heights.

Don't forget that noteHeightOfRowsWithIndexesChanged: animates by default. To make it not animate:

[NSAnimationContext beginGrouping];
[[NSAnimationContext currentContext] setDuration:0];
[tableView noteHeightOfRowsWithIndexesChanged:indexSet];
[NSAnimationContext endGrouping];

PS: I respond more to questions posted on the Apple Dev Forums than stack overflow.

PSS: I wrote the view based NSTableView