dart - RenderRepaintBoundary 到图像而不将小部件添加到屏幕

Question

我正在尝试从小部件导出图像而不将此小部件添加到屏幕。
这甚至可能吗？
我已经通过添加到可滚动容器成功导出它，现在我想渲染它而不将其添加到屏幕并将其保存到临时文件以供共享。
我认为那里应该有一个“油漆”电话，但无法弄清楚确切的位置。

这是我的代码:

var shareImage = await ShareImageWidget.builder(context,
item: item, definition: definition);
var widget = shareImage.build(context);
var repaint = RepaintBoundary.wrap(widget, 0);
var render = RenderRepaintBoundary(child:repaint.createRenderObject(context));
ui.Image image = await render.toImage(pixelRatio: 1.0);
ByteData byteData = await image.toByteData(format:ui.ImageByteFormat.png);
var pngBytes = byteData.buffer.asUint8List();
var bs64 = base64Encode(pngBytes);
var dir = await getTemporaryDirectory();

Answer 1

例子:

/// 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();
}

引用: https://github.com/flutter/flutter/issues/40064#issuecomment-620081426
有一个具有此功能的软件包: https://pub.dev/packages/screenshot#capturing-widgets-that-are-not-in-the-widget-tree