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This extracts the sample code out from the API doc comments, and places them in separate files on disk, allowing running of the examples locally, testing them, and building of slightly larger examples.
75 lines
2.9 KiB
Dart
75 lines
2.9 KiB
Dart
// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Template: dev/snippets/config/templates/freeform.tmpl
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//
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// Comment lines marked with "▼▼▼" and "▲▲▲" are used for authoring
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// of samples, and may be ignored if you are just exploring the sample.
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// Flutter code sample for BuildOwner
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//
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//***************************************************************************
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//* ▼▼▼▼▼▼▼▼ description ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)
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// This example shows how to build an off-screen widget tree used to measure
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// the layout size of the rendered tree. For some use cases, the simpler
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// [Offstage] widget may be a better alternative to this approach.
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//* ▲▲▲▲▲▲▲▲ description ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
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//***************************************************************************
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//****************************************************************************
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//* ▼▼▼▼▼▼▼▼ code-imports ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)
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import 'package:flutter/rendering.dart';
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import 'package:flutter/widgets.dart';
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//* ▲▲▲▲▲▲▲▲ code-imports ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
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//****************************************************************************
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//********************************************************************
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//* ▼▼▼▼▼▼▼▼ code ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)
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void main() {
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WidgetsFlutterBinding.ensureInitialized();
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print(measureWidget(const SizedBox(width: 640, height: 480)));
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}
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Size measureWidget(Widget widget) {
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final PipelineOwner pipelineOwner = PipelineOwner();
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final MeasurementView rootView = pipelineOwner.rootNode = MeasurementView();
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final BuildOwner buildOwner = BuildOwner(focusManager: FocusManager());
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final RenderObjectToWidgetElement<RenderBox> element =
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RenderObjectToWidgetAdapter<RenderBox>(
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container: rootView,
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debugShortDescription: '[root]',
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child: widget,
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).attachToRenderTree(buildOwner);
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try {
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rootView.scheduleInitialLayout();
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pipelineOwner.flushLayout();
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return rootView.size;
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} finally {
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// Clean up.
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element.update(RenderObjectToWidgetAdapter<RenderBox>(container: rootView));
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buildOwner.finalizeTree();
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}
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}
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class MeasurementView extends RenderBox
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with RenderObjectWithChildMixin<RenderBox> {
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@override
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void performLayout() {
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assert(child != null);
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child!.layout(const BoxConstraints(), parentUsesSize: true);
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size = child!.size;
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}
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@override
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void debugAssertDoesMeetConstraints() => true;
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}
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//* ▲▲▲▲▲▲▲▲ code ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
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//********************************************************************
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