| 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 'package:flutter/material.dart'; |
| 6 | import 'package:flutter/rendering.dart'; |
| 7 | |
| 8 | /// Flutter code sample for [BuildOwner]. |
| 9 | |
| 10 | void main() { |
| 11 | WidgetsFlutterBinding.ensureInitialized(); |
| 12 | final Size size = measureWidget(const SizedBox(width: 640, height: 480)); |
| 13 | |
| 14 | // Just displays the size calculated above. |
| 15 | runApp( |
| 16 | WidgetsApp( |
| 17 | title: 'BuildOwner Sample', |
| 18 | color: const Color(0xff000000), |
| 19 | builder: (BuildContext context, Widget? child) { |
| 20 | return Scaffold( |
| 21 | body: Center( |
| 22 | child: Text(size.toString()), |
| 23 | ), |
| 24 | ); |
| 25 | }, |
| 26 | ), |
| 27 | ); |
| 28 | } |
| 29 | |
| 30 | Size measureWidget(Widget widget) { |
| 31 | final PipelineOwner pipelineOwner = PipelineOwner(); |
| 32 | final MeasurementView rootView = pipelineOwner.rootNode = MeasurementView(); |
| 33 | final BuildOwner buildOwner = BuildOwner(focusManager: FocusManager()); |
| 34 | final RenderObjectToWidgetElement<RenderBox> element = RenderObjectToWidgetAdapter<RenderBox>( |
| 35 | container: rootView, |
| 36 | debugShortDescription: '[root]', |
| 37 | child: widget, |
| 38 | ).attachToRenderTree(buildOwner); |
| 39 | try { |
| 40 | rootView.scheduleInitialLayout(); |
| 41 | pipelineOwner.flushLayout(); |
| 42 | return rootView.size; |
| 43 | } finally { |
| 44 | // Clean up. |
| 45 | element.update(RenderObjectToWidgetAdapter<RenderBox>(container: rootView)); |
| 46 | buildOwner.finalizeTree(); |
| 47 | } |
| 48 | } |
| 49 | |
| 50 | class MeasurementView extends RenderBox with RenderObjectWithChildMixin<RenderBox> { |
| 51 | @override |
| 52 | void performLayout() { |
| 53 | assert(child != null); |
| 54 | child!.layout(const BoxConstraints(), parentUsesSize: true); |
| 55 | size = child!.size; |
| 56 | } |
| 57 | |
| 58 | @override |
| 59 | void debugAssertDoesMeetConstraints() => true; |
| 60 | } |
| 61 |