Flutter extended_image：在构建过程中调用 setState() 或 markNeedsBuild()

Question

我正在使用包 homebrew 从网络加载图像并在加载或出错时显示闪烁。

当我尝试在 setState() or markNeedsBuild() called during build 中调用 setState 时遇到此错误 loadStateChanged

事实上，我有两个小部件，一个 VideoThumbnail 负责从网络加载缩略图，另一个 VideoDesc 应该显示缩略图说明。

但我希望描述在图片加载失败或加载时间较长时显示微光。

我在 VideoThumbnail 小部件上创建了两个状态变量，它们应该传递给 VideoDesc 小部件

videoLoading = true;
videoError = false;

这是我遵循 repo 示例的代码：

视频缩略图状态

class _VideoThumbnailState extends State<VideoThumbnail>
    with SingleTickerProviderStateMixin {
  bool videoLoading;
  bool videoError;

  AnimationController _controller;

  @override
  void initState() {
    videoLoading = true;
    videoError = false;

    _controller = AnimationController(
      vsync: this,
      duration: const Duration(seconds: 3),
    );
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_) {
      print("Build Process Complete");
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      width: widget.width,
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          ClipRRect(
            borderRadius: BorderRadius.circular(4.0),
            child: ExtendedImage.network(
              widget.videoUrl,
              width: widget.width,
              height: (widget.width) * 3 / 4,
              loadStateChanged: (ExtendedImageState state) {
                switch (state.extendedImageLoadState) {
                  case LoadState.loading:
                    _controller.reset();

                    setState(() {
                      videoError = false;
                      videoLoading = true;
                    });

                    return Shimmer.fromColors(
                      child: Container(
                        decoration: BoxDecoration(
                          borderRadius: BorderRadius.circular(4.0),
                        ),
                      ),
                      baseColor: Colors.black12,
                      highlightColor: Colors.white24,
                    );
                    break;

                  case LoadState.completed:
                    _controller.forward();

                    setState(() {
                      videoError = false;
                      videoLoading = false;
                    });

                    return FadeTransition(
                      opacity: _controller,
                      child: ExtendedRawImage(
                        image: state.extendedImageInfo?.image,
                        width: widget.width,
                        height: (widget.width) * 3 / 4,
                      ),
                    );

                    break;

                  case LoadState.failed:
                    _controller.reset();
                    state.imageProvider.evict();

                    setState(() {
                      videoError = true;
                      videoLoading = false;
                    });

                    return Container(
                      width: widget.width,
                      height: (widget.width) * 3 / 4,
                      decoration: BoxDecoration(
                        image: DecorationImage(
                          image: AssetImage("assets/img/not-found.png"),
                          fit: BoxFit.fill,
                        ),
                      ),
                    );

                    break;

                  default:
                    return Container();
                }
              },
            ),
          ),
          VideoDesc(
            desc: widget.desc,
            videoError: videoError,
            videoLoading: videoLoading,
          )
        ],
      ),
    );
  }
}

视频小部件

class VideoDesc extends StatelessWidget {
  final String desc;
  final bool videoLoading;
  final bool videoError;

  const VideoDesc({
    Key key,
    @required this.desc,
    this.videoLoading = true,
    this.videoError = false,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: videoError || videoLoading
          ? Shimmer.fromColors(
              baseColor: Colors.grey[700],
              highlightColor: Colors.white24,
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  SizedBox(height: 12.0),
                  Container(
                    width: double.infinity,
                    height: 8.0,
                    decoration: BoxDecoration(
                      color: Colors.grey[900],
                      borderRadius: BorderRadius.circular(2.0),
                    ),
                  ),
                  SizedBox(height: 12.0),
                  Container(
                    width: 80.0,
                    height: 8.0,
                    decoration: BoxDecoration(
                      color: Colors.grey[900],
                      borderRadius: BorderRadius.circular(2.0),
                    ),
                  ),
                ],
              ),
            )
          : Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                SizedBox(height: 12.0),
                Text(
                  desc,
                  style: TextStyle(
                    color: Colors.white,
                    fontSize: 11.0,
                  ),
                  overflow: TextOverflow.ellipsis,
                ),
                SizedBox(height: 5.0),
                Text(
                  "361,143,203 views",
                  style: TextStyle(
                    color: Colors.white54,
                    fontSize: 12.0,
                  ),
                ),
              ],
            ),
    );
  }
}

谁能帮我解决这个问题？或者，如果有更好的方法来获取 extendedImageLoadState 值并将其传递给另一个小部件而不调用 loadStateChanged

内的 setState

Answer 1

您不能在构建过程中调用 setState。

如果您确实需要，您可以改为使用：

WidgetsBinding.instance.addPostFrameCallback(() => setState((){}));

但是，请记住，将它放在您的 switch-case 上会安排无限循环的重建，而这也是您不想要的。

我建议您重新构建您的 UI 逻辑或至少使其成为有条件的：

if(!videoLoading) {
 WidgetsBinding.instance.addPostFrameCallback(() => setState((){
        videoError = false;
        videoLoading = true;  
}));
}