I have a UICollectionView with random cells. Is there any method that allows me to center rows?

This is how it looks by default: 

[ x x x x x x ]  
[ x x x x x x ]  
[ x x         ]

Here is what the desired layout looks like: 

[ x x x x x ]  
[ x x x x x ]  
[    x x    ]
ios objective-c uicollectionview
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