Question

我在一个项目中，当我按“书签”图标时，图像应传递到Saved.dart页面。下面的代码包含一个书签图标。每当我按该图标时，它都应将图像传递到saved.dart页面，但不应将其（应在按下时不打开Saved.dart页面）推到Saved.dart页面。

import 'package:flutter/material.dart';
import 'dart:async';
import 'package:flutter/services.dart';
import 'package:image_downloader/image_downloader.dart';
import 'downloadingPage.dart';

class FullScreen extends StatefulWidget {
  String imgUrl;
  FullScreen({this.imgUrl});

  @override
  FullScreenState createState() => FullScreenState(imgUrl);
}

class FullScreenState extends State<FullScreen> {
  Color colour = Colors.black;
  Color colour2 = Colors.red;
  Color colour3 = Colors.black;
  bool isSaved = false;

  String imgUrl;
  FullScreenState(this.imgUrl);

  String message = "";
  String path = "";
  int _progress = 0;

  @override
  void initState() {
    super.initState();
    events = new StreamController<int>.broadcast();

    events.add(0);

    ImageDownloader.callback(onProgressUpdate: (String imageId, int progress) {
      setState(() {
        print("progress $progress");
        _progress = progress;
        events.add(progress);
        if (progress == 100) {
          Navigator.pop(context);
        }
      });
    });
  }

  @override
  void dispose() {
    events.close();
    super.dispose();
  }

  Future<void> _downloadImage(String url,
      {AndroidDestinationType destination, bool whenError = false}) async {
    String fileName;
    String path;
    try {
      String imageId;

      if (whenError) {
        imageId = await ImageDownloader.downloadImage(url).catchError((error) {
          if (error is PlatformException) {
            var path = "";
            if (error.code == "404") {
              print("Not Found Error.");
            } else if (error.code == "unsupported_file") {
              print("UnSupported FIle Error.");
              path = error.details["unsupported_file_path"];
            }
            setState(() {
              message = error.toString();
              path = path;
            });
          }

          print(error);
        }).timeout(Duration(seconds: 10), onTimeout: () {
          print("timeout");
        });
      } else {
        if (destination == null) {
          imageId = await ImageDownloader.downloadImage(url);
        } else {
          imageId = await ImageDownloader.downloadImage(
            url,
            destination: destination,
          );
        }
      }

      if (imageId == null) {
        print("imageId is null");
        return;
      }
      fileName = await ImageDownloader.findName(imageId);
      path = await ImageDownloader.findPath(imageId);
    } on PlatformException catch (error) {
      setState(() {
        message = error.message;
      });
      return;
    }

    if (!mounted) return;
    setState(() {
      message = 'Image Downloaded';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            RaisedButton(
              onPressed: () {
                events.add(0);
                _downloadImage(imgUrl);
                showDialog(
                  context: context,
                  builder: (_) => FunkyOverlay(
                    progress: _progress,
                    message: message,
                  ),
                );
              },
              child: Text("download"),
            ),
            IconButton(
                icon: Icon(
                  Icons.bookmark,
                  color: colour,
                ),
                onPressed: () {
                <-----when user press this icon the current image shold be passed to saved page----->
                })
          ],
        ),
      ),
    );
  }
}

以下代码已保存。dart

import 'package:flutter/material.dart';

class Saved extends StatefulWidget {
  @override
  _SavedState createState() => _SavedState();
}

class _SavedState extends State<Saved> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body:Container(
        // here the images should be displayed
      )
    );
  }
}

Answer 1

您不能将任何东西传递给未初始化的小部件。从技术上讲，该小部件在您调用它之前甚至都不存在。

您将必须将Image保存在变量中。然后当您最终导航到该屏幕时将其传递。

Answer 2

通过命名路线打开页面时可以传递参数：

应用中的命名路线：

MaterialApp(
  routes: {
    ExtractArgumentsScreen.routeName: (context) => ExtractArgumentsScreen(),
  },
);

传递参数对象，例如您的图片：

  onPressed: () {
    // When the user taps the button, navigate to a named route
    // and provide the arguments as an optional parameter.
    Navigator.pushNamed(
      context,
      ExtractArgumentsScreen.routeName,
      arguments: ScreenArguments(
        'Extract Arguments Screen',
        'This message is extracted in the build method.',
      ),
    );
  },

在您保存的.dart页面中接收参数：

class ExtractArgumentsScreen extends StatelessWidget {
  static const routeName = '/extractArguments';

  @override
  Widget build(BuildContext context) {
    // Extract the arguments from the current ModalRoute settings and cast
    // them as ScreenArguments.
    final ScreenArguments args = ModalRoute.of(context).settings.arguments;

    return Scaffold(
      appBar: AppBar(
        title: Text(args.title),
      ),
      body: Center(
        child: Text(args.message),
      ),
    );
  }
}

来源：https://flutter.dev/docs/cookbook/navigation/navigate-with-arguments

按下图标时如何在屏幕之间传递数据

2 个答案: