Example: Fade-in text effect

The following example shows how to add a fade-in effect to existing UI
using an implicitly animated widget called AnimatedOpacity.
The example begins with no animation code—it
consists of a Material App home screen containing:

A photograph of an owl.

One Show details button that does nothing when clicked.

Description text of the owl in the photograph.

Fade-in (starter code)

Click the Run button to run the example:

Animate opacity with AnimatedOpacity widget

This section contains a list of steps you can use to add an
  implicit animation to the
  fade-in starter code. After the steps, you can also run the
  fade-in complete code with the changes already made.
  The steps outline how to use the AnimatedOpacity
  widget to add the following animation feature:

The owl’s description text remains hidden until the user clicks the
Show details button.