Flutter网页端图片裁剪插件image_cropper_plus_for_web的使用

在Flutter中，image_cropper_plus_for_web 是一个用于网页端图片裁剪的插件。本文将通过一个完整的示例代码展示如何使用该插件来实现图片上传与裁剪功能。

使用步骤

1. 添加依赖

首先，在 pubspec.yaml 文件中添加以下依赖：

dependencies:
  image_cropper_plus: ^<版本号>
  image_picker: ^<版本号>

然后运行以下命令安装依赖：

flutter pub get

2. 完整示例代码

以下是完整的示例代码，展示了如何使用 image_cropper_plus_for_web 插件进行图片裁剪。

import 'package:dotted_border/dotted_border.dart';
import 'package:flutter/material.dart';
import 'package:image_cropper_plus/image_cropper_plus.dart';
import 'package:image_picker/image_picker.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  [@override](/user/override)
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        highlightColor: const Color(0xFFD0996F),
        canvasColor: const Color(0xFFFDF5EC),
        textTheme: TextTheme(
          headlineSmall: ThemeData.light().textTheme.headlineSmall!.copyWith(color: const Color(0xFFBC764A)),
        ),
        iconTheme: IconThemeData(color: Colors.grey[600]),
        appBarTheme: const AppBarTheme(
          backgroundColor: Color(0xFFBC764A),
          centerTitle: false,
          foregroundColor: Colors.white,
          actionsIconTheme: IconThemeData(color: Colors.white),
        ),
        elevatedButtonTheme: ElevatedButtonThemeData(
          style: ButtonStyle(
            backgroundColor: MaterialStateColor.resolveWith((states) => const Color(0xFFBC764A)),
          ),
        ),
        outlinedButtonTheme: OutlinedButtonThemeData(
          style: ButtonStyle(
            foregroundColor: MaterialStateColor.resolveWith((states) => const Color(0xFFBC764A)),
            side: MaterialStateBorderSide.resolveWith((states) => const BorderSide(color: Color(0xFFBC764A))),
          ),
        ),
        colorScheme: ColorScheme.fromSwatch(primarySwatch: Colors.blue).copyWith(background: const Color(0xFFFDF5EC)),
      ),
      home: const MyHomePage(title: 'Image Cropper Demo'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  [@override](/user/override)
  Widget build(BuildContext context) {
    final screenWidth = MediaQuery.of(context).size.width;
    if (screenWidth > 700) {
      return _HomePage(
        key: const ValueKey('desktop'),
        title: title,
        displayStyle: PageDisplayStyle.desktop,
      );
    } else {
      return _HomePage(
        key: const ValueKey('mobile'),
        title: title,
        displayStyle: PageDisplayStyle.mobile,
      );
    }
  }
}

enum PageDisplayStyle {
  desktop,
  mobile,
}

class _HomePage extends StatefulWidget {
  final PageDisplayStyle displayStyle;
  final String title;

  const _HomePage({
    Key? key,
    required this.displayStyle,
    required this.title,
  }) : super(key: key);

  [@override](/user/override)
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<_HomePage> {
  String? _uploadedBlobUrl;
  String? _croppedBlobUrl;

  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: widget.displayStyle == PageDisplayStyle.mobile
          ? AppBar(title: Text(widget.title))
          : null,
      body: Column(
        mainAxisSize: MainAxisSize.max,
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          if (widget.displayStyle == PageDisplayStyle.desktop)
            Padding(
              padding: const EdgeInsets.symmetric(horizontal: 24.0, vertical: 24.0),
              child: Text(
                widget.title,
                style: Theme.of(context).textTheme.displayMedium!.copyWith(color: Theme.of(context).highlightColor),
              ),
            ),
          Expanded(child: _body()),
        ],
      ),
    );
  }

  Widget _body() {
    if (_croppedBlobUrl != null || _uploadedBlobUrl != null) {
      return _imageCard();
    } else {
      return _uploaderCard();
    }
  }

  Widget _imageCard() {
    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          Card(
            elevation: 4.0,
            child: Padding(
              padding: const EdgeInsets.all(24.0),
              child: _image(),
            ),
          ),
          const SizedBox(height: 24.0),
          _menu(),
        ],
      ),
    );
  }

  Widget _image() {
    final screenWidth = MediaQuery.of(context).size.width;
    final screenHeight = MediaQuery.of(context).size.height;
    if (_croppedBlobUrl != null) {
      return ConstrainedBox(
          constraints: BoxConstraints(
            maxWidth: 0.8 * screenWidth,
            maxHeight: 0.7 * screenHeight,
          ),
          child: Image.network(_croppedBlobUrl!));
    } else if (_uploadedBlobUrl != null) {
      return ConstrainedBox(
        constraints: BoxConstraints(
          maxWidth: 0.8 * screenWidth,
          maxHeight: 0.7 * screenHeight,
        ),
        child: Image.network(_uploadedBlobUrl!),
      );
    } else {
      return const SizedBox.shrink();
    }
  }

  Widget _menu() {
    return Row(
      mainAxisSize: MainAxisSize.min,
      children: [
        FloatingActionButton(
          onPressed: () {
            _clear();
          },
          backgroundColor: Colors.redAccent,
          tooltip: 'Delete',
          child: const Icon(Icons.delete),
        ),
        if (_croppedBlobUrl == null)
          Padding(
            padding: const EdgeInsets.only(left: 32.0),
            child: FloatingActionButton(
              onPressed: () {
                _cropImage();
              },
              backgroundColor: const Color(0xFFBC764A),
              tooltip: 'Crop',
              child: const Icon(Icons.crop),
            ),
          )
      ],
    );
  }

  Widget _uploaderCard() {
    return Center(
      child: Card(
        elevation: 4.0,
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(16.0),
        ),
        child: SizedBox(
          width: 380.0,
          height: 300.0,
          child: Column(
            mainAxisSize: MainAxisSize.max,
            crossAxisAlignment: CrossAxisAlignment.center,
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              DottedBorder(
                radius: const Radius.circular(12.0),
                borderType: BorderType.RRect,
                dashPattern: const [8, 4],
                color: Theme.of(context).highlightColor.withOpacity(0.4),
                child: Padding(
                  padding: const EdgeInsets.all(24.0),
                  child: Column(
                    mainAxisSize: MainAxisSize.min,
                    crossAxisAlignment: CrossAxisAlignment.center,
                    children: [
                      Icon(
                        Icons.image,
                        color: Theme.of(context).highlightColor,
                        size: 80.0,
                      ),
                      const SizedBox(height: 24.0),
                      Text(
                        'Upload an image to start',
                        style: Theme.of(context).textTheme.headlineSmall!.copyWith(
                              color: Theme.of(context).highlightColor,
                            ),
                      )
                    ],
                  ),
                ),
              ),
              const SizedBox(height: 24.0),
              ElevatedButton(
                onPressed: () {
                  _uploadImage();
                },
                style: ElevatedButton.styleFrom(foregroundColor: Colors.white),
                child: const Text('Upload'),
              ),
            ],
          ),
        ),
      ),
    );
  }

  Future<void> _cropImage() async {
    if (_uploadedBlobUrl != null) {
      WebUiSettings settings;
      if (widget.displayStyle == PageDisplayStyle.mobile) {
        final screenWidth = MediaQuery.of(context).size.width;
        final screenHeight = MediaQuery.of(context).size.height;
        settings = WebUiSettings(
          context: context,
          presentStyle: CropperPresentStyle.page,
          boundary: CroppieBoundary(
            width: (screenWidth * 0.9).round(),
            height: (screenHeight * 0.8).round(),
          ),
          viewPort: const CroppieViewPort(
            width: 480,
            height: 480,
          ),
          enableExif: true,
          enableZoom: true,
          showZoomer: true,
        );
      } else {
        settings = WebUiSettings(
          context: context,
          presentStyle: CropperPresentStyle.dialog,
          boundary: const CroppieBoundary(
            width: 520,
            height: 520,
          ),
          viewPort: const CroppieViewPort(
            width: 480,
            height: 480,
          ),
          enableExif: true,
          enableZoom: true,
          showZoomer: true,
        );
      }
      final croppedFile = await ImageCropper().cropImage(
        sourcePath: _uploadedBlobUrl!,
        compressFormat: ImageCompressFormat.jpg,
        compressQuality: 100,
        uiSettings: [settings],
      );
      if (croppedFile != null) {
        setState(() {
          _croppedBlobUrl = croppedFile.path;
        });
      }
    }
  }

  Future<void> _uploadImage() async {
    final pickedFile = await ImagePicker().pickImage(source: ImageSource.gallery);
    if (pickedFile != null) {
      final blobUrl = pickedFile.path;
      debugPrint('picked blob: $blobUrl');
      setState(() {
        _uploadedBlobUrl = blobUrl;
      });
    }
  }

  void _clear() {
    setState(() {
      _uploadedBlobUrl = null;
      _croppedBlobUrl = null;
    });
  }
}