Can't programmatically set NSConstraints on view

Question

I'm trying to do something very simple: Creating a view from scratch, adding it to the controller's view, and have it stretch edge to edge to its superview, but I get console warning once the app runs, saying the constraints cannot be simultaneously added to the view.

    backView = [UIView new];
    backView.backgroundColor = [UIColor redColor];
    [[self view] insertSubview:backView aboveSubview:tableview];
    [[self view] addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-0-[back]-0-|"
                                                                        options:0
                                                                        metrics:nil
                                                                          views:@{@"back": backView}]];

     [[self view] addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-0-[back]-0-|"
                                                                         options:0
                                                                         metrics:nil
                                                                           views:@{@"back": backView}]];

Answer 1

When you create a UIView in code it translates auto-resizing mask to constraints.

i.e. it takes the frame you gave it when you created it and the auto-resizing mask and converts them into NSLayoutConstraints.

These auto-generated constraints are then conflicting with the constraints that you are adding manually.

If I'm right then you will be able to fix it by adding the line...

backView.translatesAutoresizingMaskIntoConstraints = NO;

right after the first line and it should fix the problem.