Animate constraint change?

[a2]

I'm trying to animate constraint changes when the user taps on a segmented control. I'm using style_classes to achieve this, but it doesn't seem to be working. I checked and, at runtime, the style_classes of the two views are changing, but nothing is happening on screen. I thought maybe it would be an immediate change, but I'm not even getting that.

Here's the code I'm using:

# from app/styles/stylesheet.rb
Teacup::Stylesheet.new :main do
  PADDING = 20

  style :onscreen,
    constraints: [
      :center_x,
      constrain(:width).equals(:superview, :width).minus(2 * PADDING),
      constrain(:bottom).equals(:segmented_control, :top).minus(PADDING),
      constrain(:top).equals(:superview, :top).plus(PADDING),
    ]

  style :offscreen_right,
    constraints: [
      constrain(:right).equals(:superview, :right).plus(500),
    ]

  style :offscreen_left,
    constraints: [
      constrain(:left).equals(:superview, :left).plus(500),
    ]
end

# from app/controllers/view_controller.rb
segmented_control.on :value_changed do |sender|
  a_styles, b_styles =
    if sender.selectedSegmentIndex == 0
      [[:onscreen], [:offscreen_right]]
    else
      [[:offscreen_left], [:onscreen]]
    end

  UIView.animateWithDuration(0.3, animations:->{
    a_view.style_classes = a_styles
    b_view.style_classes = b_styles
  })
end

[colinta]

As much as I want to promote constraints, they are MUCH more complicated than using frames, especially in animations.

What needs to be done here is you need to either replace or modify the constraints that are on the view. I've always wanted to have this be something Teacup does for you, but I haven't figured out how to approach it. Maybe try using the identifier method to give each constraint a name, so you can find/modify/remove it later.

In your animate block, call layoutIfNeeded on the view.

[colinta]

This might help:

http://kingscocoa.com/tutorials/autolayout-animations/