I have a vertical split view that does not use auto layout or constraints. The
split view contains a custom subview that has the autoresizing mask set to
NSViewWidthSizable.
During normal operation the user moves the split view divider which results in
a collapsed subview. When the split view divider is repositioned to expose the
subview, the size of the subview has been corrupted.
Apparently this is a well known historical problem caused when a superview
collapses a subview. This issue has been extensively addressed by BWSplitView
but RBSplitView but these projects are very old and have not been kept up to
date.
After thinking about it and doing a little investigation it appears that the
root cause of the problem is that the size of a view is never allowed to go
negative when autoresizing. My guess is that if the size of a subview is
allowed to go negative it would simply fix the issue.
In my subview custom class I implemented the following method override.
- (void)resizeWithOldSuperviewSize:(NSSize)oldSize
{
NSRect frame = self.frame;
NSRect superFrame = self.superview.frame;
NSAutoresizingMaskOptions mask = self.autoresizingMask;
if (mask == NSViewWidthSizable) {
CGFloat delta = superFrame.size.width - oldSize.width;
CGFloat x = frame.origin.x;
CGFloat y = frame.origin.y;
CGFloat w = frame.size.width + delta;
CGFloat h = frame.size.height;
self.frame = NSMakeRect(x, y, w, h);
}
else {
[super resizeWithOldSuperviewSize:oldSize];
}
}
This extremely simple solution seems to work perfectly. The subview collapses
to zero and then the size goes negative. When the subview is uncovered, its
size has not been corrupted and autoresizing works as expected.
So it appears that simply allowing the the size of a subview to go negative
when autoresizing fixes an issue that has been around since the days of
NeXTSTEP. So what am I missing?
--Richard Charles
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