// Copyright 2015 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'basic.dart'; import 'framework.dart'; /// A widget whose child can be mutated. class Placeholder extends StatefulWidget { /// Creates a widget whose child can be mutated. Placeholder({ Key key }) : super(key: key); @override PlaceholderState createState() => new PlaceholderState(); } /// State for a [Placeholder] widget. /// /// Useful for setting the child currently displayed by this placeholder widget. class PlaceholderState extends State<Placeholder> { /// The child that this widget builds. /// /// Mutating this field will cause this widget to rebuild with the new child. Widget get child => _child; Widget _child; set child(Widget child) { if (_child == child) return; setState(() { _child = child; }); } @override Widget build(BuildContext context) { if (_child != null) return child; return new SizedBox(width: 0.0, height: 0.0); } }