title: In a firebase animated list, is there a way to let firebase list know the expected height of a widget before it loads?
body: <p>Is there a way to explicitly tell a firebase animated list what the height of a specific widget should be? In my case, each item in the firebase list has a variable size based on a number of children (it's a comment thread). Whenever a large thread is out (above) of the viewport it is disposed of and the height is forgotten, this leads to annoying blocking and failure when trying to scroll back up. </p>
  
  <p>Here is my thread: </p>
  
  <pre><code>new FirebaseAnimatedList(
          defaultChild: new DefaultThreadView(),
          query: ref.child(postKey),
          sort: (a, b) =&gt; (a.key.compareTo(b.key)),
          itemBuilder: (context, DataSnapshot snapshot,
              Animation&lt;double&gt; animation) {
            return new FutureBuilder&lt;DataSnapshot&gt;(
                future: ref.child(postKey).child(snapshot.key).once(),
                builder: (BuildContext context,
                    AsyncSnapshot&lt;DataSnapshot&gt; snap) {
                  switch (snap.connectionState) {
                    case ConnectionState.none:
                      return new Center(
                          child: new CircularProgressIndicator());
                    case ConnectionState.waiting:
                      return new Center(
                          child: new CircularProgressIndicator());
                    default:
                      if (!snap.hasData) {
                        return new Text('Error: ${snap.error}');
                      }
                      else {
                        //check if this snap is a root node
                        String parent = snap.data.value['parent'];
  
                        if (parent == this.postKey) {
                          return new replyTile.ReplyTile(
                              snap.data, animation, this.postKey, 0);
                        } else {
                          return new Container();
                        }
                      }
                  }
                }
            );
          }
  
      )
  </code></pre>
  
  <p>the reply tile is a widget to display the data and checks if it has any children and if it does it recurses. </p>
  
  <p>Whenever a top parent reply tile goes out of the viewport it is disposed as expected but when trying to bring it back into view it scrolls right to the top and looks very jumpy, even worse whenever a bigger thread(with multiple children) tries to come back into view it doesn't scroll at all.</p>
  
  <p>I think if the list view was aware of the height the scroll problem would go away but I could be wrong</p>
  
  <p>Worse case how do I make it so the widget is not exposed and the whole thread is loaded from the start?</p>