Content padding in custom view with Cocoa auto layout - objective-c

Question

I have a custom NSView subclass which has a border around itself. The border is drawn inside this view. Is it possible to respect this borders with auto layout?
For example, when I place the subview to my custom view and set constraints like this:
#"H:|-(myViewSubView)-|" (not #"H:|-(myViewBorderWidth)-(myViewSubView)-(myViewBorderWidth)-|")
#"V:|-(myViewSubView)-|"
the layout must be:
Horizontal: |-(myViewBorderWidth)-|myViewSubview|-(myViewBorderWidth)-|
Vertical: |-(myViewBorderWidth)-|myViewSubview|-(myViewBorderWidth)-|
I've tried to overwrite -bounds method in my view to return the bounds rect without the borders, but it doesn't help.

Answer 1

UPDATE
I just noticed that your question is talking about NSView (OS X), not UIView (iOS). Well, this idea should still be applicable, but you won't be able to drop my code into your project unchanged. Sorry.
ORIGINAL
Consider changing your view hierarchy. Let's say your custom bordered view is called BorderView. Right now you're adding subviews directly to BorderView and creating constraints between the BorderView and its subviews.
Instead, give the BorderView a single subview, which it exposes in its contentView property. Add your subviews to the contentView instead of directly to the BorderView. Then the BorderView can lay out its contentView however it needs to. This is how UITableViewCell works.
Here's an example:
#interface BorderView : UIView
#property (nonatomic, strong) IBOutlet UIView *contentView;
#property (nonatomic) UIEdgeInsets borderSize;
#end
If we're using a xib, then we have the problem that IB doesn't know that it should add subviews to the contentView instead of directly to the BorderView. (It does know this for UITableViewCell.) To work around that, I've made contentView an outlet. That way, we can create a separate, top-level view to use as the content view, and connect it to the BorderView's contentView outlet.
To implement BorderView this way, we'll need an instance variable for each of the four constraints between the BorderView and its contentView:
#implementation BorderView {
NSLayoutConstraint *topConstraint;
NSLayoutConstraint *leftConstraint;
NSLayoutConstraint *bottomConstraint;
NSLayoutConstraint *rightConstraint;
UIView *_contentView;
}
The contentView accessor can create the content view on demand:
#pragma mark - Public API
- (UIView *)contentView {
if (!_contentView) {
[self createContentView];
}
return _contentView;
}
And the setter can replace an existing content view, if there is one:
- (void)setContentView:(UIView *)contentView {
if (_contentView) {
[self destroyContentView];
}
_contentView = contentView;
[self addSubview:contentView];
}
The borderSize setter needs to arrange for the constraints to be updated and for the border to be redrawn:
- (void)setBorderSize:(UIEdgeInsets)borderSize {
if (!UIEdgeInsetsEqualToEdgeInsets(borderSize, _borderSize)) {
_borderSize = borderSize;
[self setNeedsUpdateConstraints];
[self setNeedsDisplay];
}
}
We'll need to draw the border in drawRect:. I'll just fill it with red:
- (void)drawRect:(CGRect)rect {
CGRect bounds = self.bounds;
UIBezierPath *path = [UIBezierPath bezierPathWithRect:bounds];
[path appendPath:[UIBezierPath bezierPathWithRect:UIEdgeInsetsInsetRect(bounds, self.borderSize)]];
path.usesEvenOddFillRule = YES;
[path addClip];
[[UIColor redColor] setFill];
UIRectFill(bounds);
}
Creating the content view is trivial:
- (void)createContentView {
_contentView = [[UIView alloc] init];
[self addSubview:_contentView];
}
Destroying it is slightly more involved:
- (void)destroyContentView {
[_contentView removeFromSuperview];
_contentView = nil;
[self removeConstraint:topConstraint];
topConstraint = nil;
[self removeConstraint:leftConstraint];
leftConstraint = nil;
[self removeConstraint:bottomConstraint];
bottomConstraint = nil;
[self removeConstraint:rightConstraint];
rightConstraint = nil;
}
The system will automatically call updateConstraints before doing layout and drawing if somebody has called setNeedsUpdateConstraints, which we did in setBorderSize:. In updateConstraints, we'll create the constraints if necessary, and update their constants based on borderSize. We also tell the system not to translate the autoresizing masks into constraints, because that tends to create unsatisfiable constraints.
- (void)updateConstraints {
self.translatesAutoresizingMaskIntoConstraints = NO;
self.contentView.translatesAutoresizingMaskIntoConstraints = NO;
[super updateConstraints];
if (!topConstraint) {
[self createContentViewConstraints];
}
topConstraint.constant = _borderSize.top;
leftConstraint.constant = _borderSize.left;
bottomConstraint.constant = -_borderSize.bottom;
rightConstraint.constant = -_borderSize.right;
}
All four constraints are created the same way, so we'll use a helper method:
- (void)createContentViewConstraints {
topConstraint = [self constrainContentViewAttribute:NSLayoutAttributeTop];
leftConstraint = [self constrainContentViewAttribute:NSLayoutAttributeLeft];
bottomConstraint = [self constrainContentViewAttribute:NSLayoutAttributeBottom];
rightConstraint = [self constrainContentViewAttribute:NSLayoutAttributeRight];
}
- (NSLayoutConstraint *)constrainContentViewAttribute:(NSLayoutAttribute)attribute {
NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:_contentView attribute:attribute relatedBy:NSLayoutRelationEqual toItem:self attribute:attribute multiplier:1 constant:0];
[self addConstraint:constraint];
return constraint;
}
#end
I have put a complete working example in this git repository.

Answer 2

For future reference, you can override NSView.alignmentRectInsets to affect the position of the layout guides:
Custom views that draw ornamentation around their content can override
this property and return insets that align with the edges of the
content, excluding the ornamentation. This allows the constraint-based
layout system to align views based on their content, rather than just
their frame.
Link to documentation:
https://developer.apple.com/documentation/appkit/nsview/1526870-alignmentrectinsets

Answer 3

Have you tried setting the intrinsic size to include the border size?
- (NSSize)intrinsicContentSize
{
return NSMakeSize(width+bordersize, height+bordersize);
}
then you would set the content compression resistance priorities in both directions to be required:
[self setContentCompressionResistancePriority:NSLayoutPriorityRequired forOrientation:NSLayoutConstraintHorizontal];
[self setContentCompressionResistancePriority:NSLayoutPriorityRequired forOrientation:NSLayoutConstraintVertical];

Answer 4

The one solution I found is to overload the addConstraint: method and modify constraints before they'll be added:
- (void)addConstraint:(NSLayoutConstraint *)constraint
{
if(constraint.firstItem == self || constraint.secondItem == self) {
if(constraint.firstAttribute == NSLayoutAttributeLeading) {
constraint.constant += self.leftBorderWidth;
} else if (constraint.firstAttribute == NSLayoutAttributeTrailing) {
constraint.constant += self.rightBorderWidth;
} else if (constraint.firstAttribute == NSLayoutAttributeTop) {
constraint.constant += self.topBorderWidth;
} else if (constraint.firstAttribute == NSLayoutAttributeBottom) {
constraint.constant += self.bottomBorderWidth;
}
}
[super addConstraint:constraint];
}
And then also handle this constraints in xxxBorderWidth setters.