x:Name=

"myImage"

/>

Then in code behind, or a behavior, this would fade in the image,
over a 1-second period.

myImage

FadeTo

1000

);

In Flutter, you animate widgets using the animation library
by wrapping widgets inside an animated widget.
Use an AnimationController, which is an Animation<double>
that can pause, seek, stop and reverse the animation.
It requires a Ticker that signals when vsync happens,
and produces a linear interpolation between 0 and 1
on each frame while it’s running.
You then create one or moreAnimations and attach them to the controller.