title: How to position a Widget at the bottom of a SingleChildScrollView?
body: <p>I need to use <code>SingleChildScrollView</code> in order to be able to use <a href="https://pub.dartlang.org/packages/keyboard_actions" rel="noreferrer">keyboard_actions</a> so that i can put a "Done" button on top of the keyboard in iOS (using a numeric keyboard at the moment)</p>
  
  <p>The <code>SingleChildScrollView</code> will have a column as a child and then a button to be placed at the bottom. I tried using <code>LayoutBuilder</code> to enforce a height to the <code>SingleChildScrollView</code>.</p>
  
  <pre class="lang-dart prettyprint-override"><code>LayoutBuilder(
        builder: (BuildContext context, BoxConstraints viewportConstraints) {
      return SingleChildScrollView(
          child: ConstrainedBox(
              constraints:
                  BoxConstraints(minHeight: viewportConstraints.maxHeight),
              child: Column(
                  crossAxisAlignment: CrossAxisAlignment.stretch,
                  mainAxisSize: MainAxisSize.max,
                  children: &lt;Widget&gt;[
                    Column(),
                    // Spacer() ?
                    FlatButton()
                  ])));
    });
  
  </code></pre>
  
  <p>I tried using the <code>BoxConstraints</code> with the <code>maxHeight</code> attribute, but ultimately the widget wouldn't scrooll up when the keyboard appeared.</p>
  
  <p>Side note: the Scaffold has both <code>resizeToAvoidBottomInset</code> and <code>resizeToAvoidBottomPadding</code> set to <code>true</code> (the default value)</p>