Is there any way to add constraint between a view

Question

In iOS 7, we can now add a constraint between a view and the top layout guide, which I think is very useful to solve the status bar offset issue in iOS7(especially when there is no navigation bar in the view).

In a storyboard file, I can add this kind of constraints easily. Just hold the control key then drag the view to the container, it will show the "Top Space to Top Layout Guide" option.

But when I do the same operation in a xib file, this option disappears.

So, is there any way to add this kind of constraints in xib files? Or do I have to add them with code?

Answer 1

From iOS 9 you can also do it more simple with topLayoutGuide's anchors:

• Swift 3

view.topAnchor.constraint(equalTo: self.topLayoutGuide.bottomAnchor).isActive = true

• ObjC

[controller.view.topAnchor constraintEqualToAnchor:controller.topLayoutGuide.bottomAnchor].active = YES;

Answer 2

You should refer the following example, this will definitely help you for your problem. I got this from http://developer.apple.com .

[button setTranslatesAutoresizingMaskIntoConstraints: NO];
id topGuide = myViewController.topLayoutGuide;
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings (button, topGuide);

[myViewController.view addConstraints:
    [NSLayoutConstraint constraintsWithVisualFormat: @"V:[topGuide]-20-[button]"
    options: 0
    metrics: nil
    views: viewsDictionary]
];

Answer 3

Of course, You can not only add constraint between a view and the top layout guide or bottom layout guide by programmatically but also you can remove and access constraint between a view and the top and bottom layout guide with the help of KVConstraintExtensionsMaster library.

// create containerView
UIView *containerView = [UIView prepareNewViewForAutoLayout];
[containerView setBackgroundColor:[UIColor brownColor]];
[self.view addSubview:containerView];

// To add Top and Bottom Layout Guide constraint of containerView
[self applyTopLayoutGuideConstraintToView:containerView withPadding:0];
[self applyBottomLayoutGuideConstraintToView:containerView withPadding:50];

// To access top Layout Guide Constraint and update it's constant value.
NSLayoutConstraint *topLayoutGuideConstraint = [self accessAppliedTopLayoutGuideConstraintFromView:containerView];
topLayoutGuideConstraint.constant = 50;

// To access bottom Layout Guide Constraint and update it's constant value with animation
NSLayoutConstraint *bottomLayoutGuideConstraint = [self accessAppliedBottomLayoutGuideConstraintFromView:containerView];
bottomLayoutGuideConstraint.constant = 80;
[self.view updateModifyConstraintsWithAnimation:NULL]; // call this for animation

// To remove Top and Bottom Layout Guide constraint of containerView
[self removeAppliedTopLayoutGuideConstraintFromView:containerView];
[self removeAppliedBottomLayoutGuideConstraintFromView:containerView ];

Answer 4

Here is my alternative solution.

Find a UIView as a pivot, set its top layout constraint a fixed vertical space to container's top.

Control-Drag this layout constraint as an IBOutlet, such as

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *topLayoutConstraint;

Finally, just override viewWillLayoutSubviews method of UIViewController like following

- (void)viewWillLayoutSubviews
{
    [super viewWillLayoutSubviews];

    self.topLayoutConstraint.constant = [self.topLayoutGuide length] + YOUR_TOP_CONSTRSINT;
}

All the other views' top constraint are based this pivot view, all done :)

Answer 5

Until now even using XCode 6 I cannot align controls to top layout guide on .xib files. Instead, I am using an alternative way.

First, on interface builder, I still align controls to top border of viewcontroler's view.

Then, in viewDidLoad method, I replace some constraints so they will align to top layout guide instead of main view:

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSArray *constraints = self.view.constraints;
    for (NSLayoutConstraint *constraint in constraints) {
        if ( (constraint.firstItem == self.view) && (constraint.firstAttribute == NSLayoutAttributeTop) ) {
            NSLayoutConstraint *newConstraint = [self constraint:constraint replaceFirstItemBy:self.topLayoutGuide attribute:NSLayoutAttributeBottom];
            [self.view removeConstraint:constraint];
            [self.view addConstraint:newConstraint];
        } else if ( (constraint.secondItem == self.view) && (constraint.secondAttribute == NSLayoutAttributeTop) ) {
            NSLayoutConstraint *newConstraint = [self constraint:constraint replaceSecondItemBy:self.topLayoutGuide attribute:NSLayoutAttributeBottom];
            [self.view removeConstraint:constraint];
            [self.view addConstraint:newConstraint];
        }
    }
}

- (NSLayoutConstraint*)constraint:(NSLayoutConstraint*)constraint replaceFirstItemBy:(id)newItem attribute:(NSLayoutAttribute)newAttribute {
    UILayoutPriority priority = constraint.priority;
    NSLayoutRelation relation = constraint.relation;
    id secondItem = constraint.secondItem;
    NSLayoutAttribute secondAttribute = constraint.secondAttribute;
    CGFloat multiplier = constraint.multiplier;
    CGFloat constant = constraint.constant;

    NSLayoutConstraint *newConstraint = [NSLayoutConstraint constraintWithItem:newItem attribute:newAttribute relatedBy:relation toItem:secondItem attribute:secondAttribute multiplier:multiplier constant:constant];
    newConstraint.priority = priority;
    return newConstraint;
}

- (NSLayoutConstraint*)constraint:(NSLayoutConstraint*)constraint replaceSecondItemBy:(id)newItem attribute:(NSLayoutAttribute)newAttribute {
    UILayoutPriority priority = constraint.priority;
    id firstItem = constraint.firstItem;
    NSLayoutAttribute firstAttribute = constraint.firstAttribute;
    NSLayoutRelation relation = constraint.relation;
    CGFloat multiplier = constraint.multiplier;
    CGFloat constant = constraint.constant;

    NSLayoutConstraint *newConstraint = [NSLayoutConstraint constraintWithItem:firstItem attribute:firstAttribute relatedBy:relation toItem:newItem attribute:newAttribute multiplier:multiplier constant:constant];
    newConstraint.priority = priority;
    return newConstraint;
}

Think this is not the best way because we replace objects that we define on interface builder. But it may be an alternative way that we can think about.

Answer 6

I think the reason they don't show up in the XIB is that there is no knowledge of the view controller hierarchy in that situation, whereas in a story board IB can tell where the guides are from the view controller hierarchy the view is in. I.e If it is contained in a UINavigationController, it can determine that the top layout guide is below the navigation toolbar.