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I've got an autolayout constraint that attaches a view just above the tab bar. The specifics of this aren't important, it works fine. 

NSDictionary *views = @{@"view":self.collectionSelectionContainer, @"bottomLayoutGuide":self.bottomLayoutGuide};
NSDictionary *metrics = @{@"offset":@(tabBarHeight)};
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[view]-offset-[bottomLayoutGuide]" options:0 metrics:metrics views:views]];

However, I want to create this constraint using the other method:

[NSLayoutConstraint constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant:]

I've tried various ways unsuccessfully. Can anybody show me how?

Thanks

share|improve this question
    
Hey mate, out of interest why aren't you connecting the bottom of 'collectionSelectionContainer' to the top of the 'tabBar' ? – Mike Pollard Sep 3 '13 at 16:19
    
Ey up Mike.... My layout constraints are in a view controller that is in a containment hierarchy. So attempting to add the constraint to the tab bar, which isn't a descendant of my view, violates the rules. – bandejapaisa Sep 3 '13 at 18:09
    
Ah, sounds complicated ... sure beats setting frames though eh! :) – Mike Pollard Sep 4 '13 at 8:41

1 Answer 1

up vote 1 down vote

I figured that I could just inspect the NSLayoutConstraint returned array from constraintsWithVisualFormat! This actually was a great way to figure it out and then build the method from there:

The answer is this:

self.collectionSelectionBottomConstraint = [NSLayoutConstraint constraintWithItem:self.bottomLayoutGuide attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.collectionSelectionContainer attribute:NSLayoutAttributeBottom multiplier:1 constant:tabBarHeight];
[self.view addConstraint:self.collectionSelectionBottomConstraint];

I think the reason I was being unsuccessful before was that I was passing 0 as the multiplier.

share|improve this answer
    
I had to use Top instead of TopMargin. That was the error in my case. – testing Oct 10 '14 at 12:39

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