Programmatically implementing two different layouts using size classes

Question

I have a four buttons layout. In portrait they should be shown one above the other. In landscape they should be in two columns each with two buttons.

I implement the but

Answer 1

You can examine the view's trait collection to determine its horizontal and vertical size class.

if (self.view.traitCollection.horizontalSizeClass == UIUserInterfaceSizeClassCompact) {
    ...
}

Implement the traitCollectionDidChange: method to automatically be called when a trait changes due to autorotation.

For more information, see UITraitCollection Class Reference and UITraitEnvironment Protocol Reference.