Answers for "RenderFlex children have non-zero flex but incoming height constraints are unbounded."

RenderFlex children have non-zero flex but incoming height constraints are unbounded.

You need to wrap your child with some height and width as some of the child are
exceeding the available height and width. you can use media query and get the 
avaailable height and width :

final _mediaQuery = MediaQuery.of(context).size;

Container(
  width: _mediaQuery.width,
  height: _mediaQuery.height * 0.4,
  child: ...
  ....
)

############ OR #############

Wrap your Column inside an Expanded or SizedBox (with some height) like this:

Expanded(
  child: Column(...)
)

OR

SizedBox(
  height: 200, // Some height
  child: Column(...),
)