Center widget vertically inside a SingleChildScrollView

Solution:

Put your top level Stack inside Center widget.

body: Center(child: Stack(
      children: _buildBody(),
    )));

Tip to debug:

Use Flutter Inspector to find where the layout is going wrong.

I edited your code a bit(to make to work in my local) and then I inspected. It showed like below

We have a Stack and SingleChildScrollView as per code(refer to the right side of the diagram where the stack of widgets are displayed). As size is determined by SingleChildScrollView(contents inside it), Stack occupies only a little space and by default, it aligned at top. So put it under Center, the whole Stack view will come in the center.

ArtiomLK Suggested a solution in comments which helped me:

wrap SingleChildScrollView in a Center. The widgets tree is:

Center( child: SingleChildScrollView( child: Column(...)))

None of the others helped.

You can use "Center" widget like as

return Center( child: SingleChildScrollView() )