| 1 | // Copyright 2014 The Flutter Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | import 'framework.dart'; |
| 6 | |
| 7 | /// Base class for stateful widgets that have exactly one inflated instance in |
| 8 | /// the tree. |
| 9 | /// |
| 10 | /// Such widgets must be given a [GlobalKey]. This key can be generated by the |
| 11 | /// subclass from its [Type] object, e.g. by calling `super(key: new |
| 12 | /// GlobalObjectKey(MyWidget))` where `MyWidget` is the name of the subclass. |
| 13 | /// |
| 14 | /// Since only one instance can be inflated at a time, there is only ever one |
| 15 | /// corresponding [State] object. That object is exposed, for convenience, via |
| 16 | /// the [currentState] property. |
| 17 | /// |
| 18 | /// When subclassing [UniqueWidget], provide the corresponding [State] subclass |
| 19 | /// as the type argument. |
| 20 | abstract class UniqueWidget<T extends State<StatefulWidget>> extends StatefulWidget { |
| 21 | /// Creates a widget that has exactly one inflated instance in the tree. |
| 22 | /// |
| 23 | /// The [key] argument is required because it identifies the unique inflated |
| 24 | /// instance of this widget. |
| 25 | const UniqueWidget({required GlobalKey<T> super.key}); |
| 26 | |
| 27 | @override |
| 28 | T createState(); |
| 29 | |
| 30 | /// The state for the unique inflated instance of this widget. |
| 31 | /// |
| 32 | /// Might be null if the widget is not currently in the tree. |
| 33 | T? get currentState { |
| 34 | final GlobalKey<T> globalKey = key! as GlobalKey<T>; |
| 35 | return globalKey.currentState; |
| 36 | } |
| 37 | } |
| 38 |