title: Alert box with multi select chip in flutter
body: <p>I have a multiselect chip in my app , but when since the data in the AlertDialog depends dynamically, it will be 1 or 100, so I have added SingleChildScrollView over the alert Dialog to give scrolling if there are more entries , but when I added <code>SingleChildScrollView</code>  my alert box goes to top of the screen like <a href="https://i.stack.imgur.com/TDzEg.png" rel="nofollow noreferrer">this</a>, I want it to align in center, </p>
  
  <p>If I removed the SingleChildScrollView then It will come like <a href="https://i.stack.imgur.com/kNpJr.png" rel="nofollow noreferrer">this</a> which I wanted. but If there are lot of entries I cant select because It cant cover the entire data?</p>
  
  <p>Is there any way where I can align it to center of screen with scroll enabled?</p>
  
  <p>Thanks</p>
  
  <pre><code>showDialog(
              context: context,
              builder: (BuildContext context) {
                return SingleChildScrollView(
                    child: AlertDialog(
                  title: Text("choose items"),
                  content: MultiSelectChip(
                    reportList,
                    onSelectionChanged: (selectedList) {
                      setState(() {
                        listSelectedItem = selectedList;
                      });
                    },
                  ),
                  actions: &lt;Widget&gt;[
                    FlatButton(
                        child: Text("CANCEL"),
                        onPressed: () {
                          setState(() {
                            dropdownSelected = null;
                            listSelectedItem.clear();
                          });
                          Navigator.of(context).pop();
                        }),
  </code></pre>