Autolayout animate x/y position of UIView without changing width/height

Question

I'm trying to get used to animation with Autolayout and constraints instead of animation with frames. In my project I have a UIView near the top of the screen that I'm trying to animate straight downward (y position). I understand that I must modify the constraint constant value, but doing so decreases the height of my view instead of "pushing" it downward like I'm wanting. Here's my code:

self.topConstraint.constant = 180;

[UIView animateWithDuration:0.5f animations:^{
    [self.theView layoutIfNeeded];
} completion:^(BOOL finished) {

}];

topConstraint is a vertical space constraint between the top of the ViewController's view and theView.

Other constraints on theView include:

• Center X Alignment

• Horizontal Space

• Vertical Space (self.topConstraint)

• Vertical Space (represents the space between theView and the bottom of the ViewController's view)

• Pinned width

• Pinned height

How do I modify the constraint values to simply change the position of theView without affecting its width/height?

Answer 1

You should remove the constraint:

Vertical Space (represents the space between theView and the bottom of the ViewController's view)

because you don't want the height to change (you have it pinned) and you are specifying the x (centre constraint) and y (other vert constraint) positions with other constraints so it isn't required.

Your Horizontal Space constraint may also not be required (because you have a Center X Alignment constraint) - the horizontal space could be required, but more likely on the view that this one is centred on.