MacOS: Cell-based NSTableView custom row height breaks rendering - macos

Question

I am attempting to update some very old, formerly functional MacOS code (Objective C, pre-10.7) to modern MacOS and XCode 13. I have an NSCell-based NSTableView with custom row heights which when compiled pre-10.7 works fine and which more recently has stopped working. Recall 10.7 was the era in which auto-layout was introduced and NSTableView revised to accomodate NSView-based cells, so it makes sense that something problematic in this formerly functional code was flushed at that point.
The symptom of "stopped working" is that my custom NSCell's drawing method (drawWithFrame:inView) is never called, and the NSTableView renders each row as an opaque rectangle two pixels high. 8 years ago someone reported a similar symptom in similar global circumstances, but this issue remained unresolved, and they are no longer active.
In Interface Builder, I have "Row Size Style: Custom" and "Content Mode: Cell Based" set. I believe auto-layout is not relevant, since NSCells do not have constraints.
Now for the bizarre part. If I remove my NSTableViewDelegate's heightOfRow method, the table render works perfectly, and custom rows render though all at a constant height.
However if I re-add an implementation as straightforward as:
- (float)tableView:(NSTableView *)tableView heightOfRow:(int)row
{
return 30.0;
}
then I can see this method being called, once per row, to accumulate their sizes but after that NSCell's draw method is never called.
On the off chance I am completely misunderstand the documentation for heightOfRow, I have tried returning numbers much larger and much smaller than 30.0 as well. No luck. The fact that the table renders perfectly with heightOfRow unimplemented makes me believe my dataSource architecture and even my custom NSCell architecture is all functional, and that the issue somehow relates specifically to how NSTableView is interpreting my table's rows.
Here's the table's config in Interface Builder:
and here's source of a (toyed-down) ViewController for the panel (a modal dialog box) that both contains the tableView and acts as its delegate:
/* A customCell, installed in our nib, allows us to do our custom rendering */
#interface CustomCell : NSCell
{
}
#end
#implementation CustomCell
- (void)drawWithFrame:(NSRect)cellFrame inView:(NSView *)controlView
{
CGContextRef quartz = [NSGraphicsContext currentContext].CGContext;
CGContextSaveGState(quartz);
CGContextSetRGBFillColor(quartz, 1.0, 0.0, 0.0, 1.0);
CGContextFillEllipseInRect(quartz, cellFrame);
CGContextRestoreGState(quartz);
}
#end
#implementation GSPRDBBrowseDialogController
#undef SHOW_THE_BUG
#ifdef SHOW_THE_BUG
/*
SHOW THE BUG: Explicitly including any definition of the
following delegate method, even one that returns a constant row
height of 30, causes our [cell drawWithFrame] method to never be called,
and all table rows appear as black rectangles 2 pixels high.
*/
- (float)tableView:(NSTableView *)tableView heightOfRow:(int)row
{
return 30;
}
#else
/* with no implementation of heightOfRow, Cocoa calls our renderer using
some the constant row height value (24 pixels) specified in the nib.
*/
#endif
- (IBAction) openButtonPressed: (id) sender
{
[NSApp stopModal];
}
- (id) initWithContext: (const RDB_Context*) iContext
helpContext: (int) iHelpContext
{
rdbContext = *iContext;
return( self = [super initWithNibNamed: #"rdbbrowse_dlg"
dialogData: NULL
changeProc: NULL
backTrack: false
helpContext: iHelpContext]);
}
- (int) numberOfRowsInTableView: (NSTableView*) iTableView
{
return 20;
}
- (id) tableView: (NSTableView*) iTableView
objectValueForTableColumn: (NSTableColumn*) iColumn
row: (int) iRow
{
return nil; // doesn't matter. real code returns more here.
}
#end
Running this code with SHOW_THE_BUG #UNDEFined produces the following correct (but undesired) result: 20 rows of red circles, each 24 pixels high:
But changing to #DEFINE SHOW_THE_BUG, thereby including a toy-implementation of heightOfRow that should set all rows to 30 pixels high, and instead we get this...thin rectangles (look closely at the top of the table), and the actual cell renderer (drawWithFrame) is never called:
Any thoughts about what crazy contortion my code may be in, where defining a custom row height that is effectively constant breaks rendering completely but leaving row height undefined produces almost-perfect results?
Thanks,
Nick

Answer 1

This wound up being my own fault. The object I was instantiating as NSTableViewDelegate, my dialog box NSWindowController, turned out to inherit from a long-forgotten base class that provides some general utilities for other dialog boxes in this app. That base class, in turn, implemented some of the NSTableViewDelegate contract, and those parts of one delegate instantiation were thus by inheritance intermingled with the various parts of the delegate contract I'm implementing here, leading to a broken contract from NSTableView's perspective. Since the base class is out of my control solution here was to firewall this table's delegate implementation into its own object, owned by but not descending from this NSWindowController, so it completely controls how much of the (optional) NSTableViewDelegate instantiation gets presented to the table.
I'm suitably sheepish and grateful to #Willeke for insisting the local implementation was itself coherent, which is what led me to wonder if the effective delegate implementation was somehow "more than" the local one...