title: showModalBottomSheet adaptive size Flutter
body: <p>I have the next problem, having a little number of children allows users to scroll even though there is an empty space</p>
  <pre><code>Future&lt;void&gt; buildScrollableSheet([Widget? header]) {
      return showModalBottomSheet(
        context: context,
        isScrollControlled: true,
        backgroundColor: Colors.transparent,
        builder: (context) =&gt; makeDismissible(
          child: DraggableScrollableSheet(
            initialChildSize: 0.3,
            maxChildSize: 0.9, // this one should be adaptive
            builder: (_, controller) =&gt; Container(
              decoration: const BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.vertical(
                  top: Radius.circular(25),
                ),
              ),
              padding: const EdgeInsets.symmetric(horizontal: 16),
              child: Column(
                // crossAxisAlignment: CrossAxisAlignment.stretch,
                children: [
                  const Padding(
                    padding: EdgeInsets.all(24),
                    child: Center(
                      child: Text(
                        'My header',
                        style: TextStyle(
                          color: Color(0xff757575),
                          fontSize: 14,
                        ),
                      ),
                    ),
                  ),
                  Flexible(
                    child: Material(
                      color: Colors.white,
                      child: ListView(
                        shrinkWrap: true,
                        controller: controller,
                        children: [
                          SimpleHeader(
                            title: 'title',
                            text: 'text',
                          ),
                          SimpleHeader(
                            title: 'title',
                            text: 'text',
                          ),
                          SimpleHeader(
                            title: 'title',
                            text: 'text',
                          ),
                        ],
                      ),
                    ),
                  ),
                ],
              ),
            ),
          ),
        ),
      );
    }
  </code></pre>
  <p>Here you can see maxChildSize is being set as 0.9 which is fine with a lot of children inside <code>ListView</code>, but in this case, there are only 3 elements and I want to prevent scrolling to full size, also it would be great to set <code>initialChildSize</code> to childs size, so if I have a huge list of items it would always open full.
  Thank you!</p>
  <p><a href="https://i.stack.imgur.com/zUKXZl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zUKXZl.png" alt="showModalBottomSheet" /></a>
  <a href="https://i.stack.imgur.com/6WM3ll.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6WM3ll.png" alt="openedModalSheet" /></a></p>