[iOS] Change the constraints value when use the auto layout

When you use the auto layout, you will set some constraints to some view. Also maybe you want to change the value in the code. Just do this:

First drag the constraint you want to change to the code area to generate a constraint property.

Then do something like this:

//change the value of the constraint
bottomMarginConstraint.constant = 10
self.view.layoutIfNeeded()