是否可以将隐藏的小部件导出为图像？答案

【问题标题】：Is it possible to export hidden widgets as an Image?是否可以将隐藏的小部件导出为图像？
【发布时间】：2019-11-16 13:31:19
【问题描述】：

我知道如何使用 RepaintBoundary 将可见小部件保存到图像中

我想要的是一种将用户看不到的widget 保存为image 的方法。

【问题讨论】：

你找到什么了吗？
没有。但我使用了一种 hack 来实现我想要的。我将RepaintBoundary 放在所有其他小部件后面，这样用户就看不到它了。
我的问题是我的 ListView 有很多项目，所以它不适合屏幕。我想制作一个所有项目都可见的宽幅图像。现在我正在尝试使用缩放：stackoverflow.com/questions/56423707/flutter-zoomable-widget

标签： android flutter dart flutter-layout

【解决方案1】：

/// Creates an image from the given widget by first spinning up a element and render tree,
/// then waiting for the given [wait] amount of time and then creating an image via a [RepaintBoundary].
/// 
/// The final image will be of size [imageSize] and the the widget will be layout, ... with the given [logicalSize].
Future<Uint8List> createImageFromWidget(Widget widget, {Duration wait, Size logicalSize, Size imageSize}) async {
  final RenderRepaintBoundary repaintBoundary = RenderRepaintBoundary();

  logicalSize ??= ui.window.physicalSize / ui.window.devicePixelRatio;
  imageSize ??= ui.window.physicalSize;

  assert(logicalSize.aspectRatio == imageSize.aspectRatio);

  final RenderView renderView = RenderView(
    window: null,
    child: RenderPositionedBox(alignment: Alignment.center, child: repaintBoundary),
    configuration: ViewConfiguration(
      size: logicalSize,
      devicePixelRatio: 1.0,
    ),
  );

  final PipelineOwner pipelineOwner = PipelineOwner();
  final BuildOwner buildOwner = BuildOwner();

  pipelineOwner.rootNode = renderView;
  renderView.prepareInitialFrame();

  final RenderObjectToWidgetElement<RenderBox> rootElement = RenderObjectToWidgetAdapter<RenderBox>(
    container: repaintBoundary,
    child: widget,
  ).attachToRenderTree(buildOwner);

  buildOwner.buildScope(rootElement);

  if (wait != null) {
    await Future.delayed(wait);
  }

  buildOwner.buildScope(rootElement);
  buildOwner.finalizeTree();

  pipelineOwner.flushLayout();
  pipelineOwner.flushCompositingBits();
  pipelineOwner.flushPaint();

  final ui.Image image = await repaintBoundary.toImage(pixelRatio: imageSize.width / logicalSize.width);
  final ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);

  return byteData.buffer.asUint8List();
}

【讨论】：