A FrameLayout with a rounded corner background and shadow.
CardView uses elevation property on Lollipop for shadows and falls back to a
custom emulated shadow implementation on older platforms.
Due to expensive nature of rounded corner clipping, on platforms before Lollipop, CardView does
not clip its children that intersect with rounded corners. Instead, it adds padding to avoid such
intersection (See setPreventCornerOverlap(boolean) to change this behavior).
Before Lollipop, CardView adds padding to its content and draws shadows to that area. This
padding amount is equal to maxCardElevation + (1 - cos45) * cornerRadius on the
sides and maxCardElevation * 1.5 + (1 - cos45) * cornerRadius on top and bottom.
Since padding is used to offset content for shadows, you cannot set padding on CardView.
Instead, you can use content padding attributes in XML or
setContentPadding(int, int, int, int) in code to set the padding between the edges of
the CardView and children of CardView.
Note that, if you specify exact dimensions for the CardView, because of the shadows, its content
area will be different between platforms before Lollipop and after Lollipop. By using api version
specific resource values, you can avoid these changes. Alternatively, If you want CardView to add
inner padding on platforms Lollipop and after as well, you can call
setUseCompatPadding(boolean) and pass true.
To change CardView's elevation in a backward compatible way, use
setCardElevation(float). CardView will use elevation API on Lollipop and before
Lollipop, it will change the shadow size. To avoid moving the View while shadow size is changing,
shadow size is clamped by getMaxCardElevation(). If you want to change elevation
dynamically, you should call setMaxCardElevation(float) when CardView is initialized.