Objective-C - drawing a horizontal line through the middle of the screen

Question

I'm trying to draw a horizontal line through the middle of the screen of an app that has a navigation bar. Here's my current code to do so:

CGFloat screenWidth = self.view.frame.size.width;
CGFloat screenHeight = self.view.frame.size.height;
CGFloat navigationBarHeight = self.navigationController.navigationBar.frame.size.height;
CGFloat lineThickness = 3;

UIView *horizontalLine = [[UIView alloc] initWithFrame:CGRectMake(0, (screenHeight - navigationBarHeight) / 2, screenWidth, lineThickness)];
[self.view addSubview:horizontalLine];

I used a very similar calculation to draw a vertical line - and that worked just fine. But, the issue is, regardless of device, this horizontal line ends up too low on the screen by roughly 10 pixels. Is there an offset I may be missing? Something to do with the navigation bar perhaps?

Answer 1

ok i did it like this first .. but it wasnt centered. but it SHOULD BE! :) under this i changed it to add a view to wrap it all and that seemed to "work" you can try either or, or a combination of some of the elements and see how that goes.

UIView *horizontalLine = [[UIView alloc] initWithFrame:CGRectZero];

[self.view addSubview:horizontalLine];

[horizontalLine setTranslatesAutoresizingMaskIntoConstraints: NO];

horizontalLine.backgroundColor = [UIColor blackColor];

id topGuide = self.topLayoutGuide;
id bottomGuide = self.bottomLayoutGuide;

NSDictionary * viewsDictionary = NSDictionaryOfVariableBindings(horizontalLine, topGuide, bottomGuide);

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[horizontalLine]|" options:0 metrics: 0 views:viewsDictionary]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[topGuide][horizontalLine(==3)][bottomGuide]|" options:0 metrics: 0 views:viewsDictionary]];


[self.view addConstraint:
 [NSLayoutConstraint constraintWithItem:horizontalLine
                              attribute:NSLayoutAttributeCenterY
                              relatedBy:NSLayoutRelationEqual
                                 toItem:self.view
                              attribute:NSLayoutAttributeCenterY
                             multiplier:1
                               constant:0]];

"wrapped" approach. it's a bit messy but it might give you some ideas of things to try

UIView * wrapper = [[UIView alloc] initWithFrame:CGRectZero];

UIView *horizontalLine = [[UIView alloc] initWithFrame:CGRectZero];

[wrapper setTranslatesAutoresizingMaskIntoConstraints: NO];
[horizontalLine setTranslatesAutoresizingMaskIntoConstraints: NO];

[self.view addSubview:wrapper];
[wrapper addSubview:horizontalLine];

horizontalLine.backgroundColor = [UIColor blackColor];

id topGuide = self.topLayoutGuide;
id bottomGuide = self.bottomLayoutGuide;

NSDictionary * viewsDictionary = NSDictionaryOfVariableBindings(horizontalLine, topGuide, bottomGuide, wrapper);

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[wrapper]|" options:0 metrics: 0 views:viewsDictionary]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[topGuide][wrapper][bottomGuide]|" options:0 metrics: 0 views:viewsDictionary]];

[wrapper addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[horizontalLine]|" options:0 metrics: 0 views:viewsDictionary]];

[wrapper addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(>=1)-[horizontalLine(==3)]-(>=1)-|" options:0 metrics: 0 views:viewsDictionary]];

[wrapper addConstraint:
 [NSLayoutConstraint constraintWithItem:horizontalLine
                              attribute:NSLayoutAttributeCenterY
                              relatedBy:NSLayoutRelationEqual
                                 toItem:wrapper
                              attribute:NSLayoutAttributeCenterY
                             multiplier:1
                               constant:0]];