1、加载资源和图片

指定资源
Flutter 使用 pubspec.yaml 文件，位于项目根目录，来识别应用程序所需的资源。

flutter:
  assets:
    - assets/my_icon.png
    - assets/background.png

flutter:
  assets:
    - directory/
    - directory/subdirectory/

import 'package:flutter/services.dart' show rootBundle;

Future<String> loadAsset() async {
  return await rootBundle.loadString('assets/config.json');
}

return const Image(image: AssetImage('assets/background.png'));

2、分辨率自适应图片资源

Flutter 可以为当前设备加载适合其 设备像素比 的图像。

AssetImage 可以将请求资源映射到最接近当前 设备像素比 的资源。

为了使这种映射起作用，资源应该根据特定的目录结构来保存：

你只需要在 pubspec.yaml 的 assets 部分指定主要资源， Flutter 会自动帮你绑定其他变体。在 pubspec.yaml 中资源部分的每一项都应与实际文件相对应，除过主资源节点。当主资源缺少某个文件时，会按分辨率从低到高的顺序去选择，也就是说 1x 中没有的话会在 2x 中找，2x 中还没有的话就在 3x 中找。该条目需要在 pubspec.yaml 中指定。

使用默认的资源 bundle 加载资源时，系统会自动处理分辨率等。（如果你使用一些更低级别的类，如 ImageStream 或 ImageCache，你需要注意 scale 相关的参数）。

然后加载 image, 使用：

return const AssetImage('icons/heart.png', package: 'my_icons');

package 使用本身的 Assets 也需要加上 package 参数来获取。

3、显示网络上的远程图片

使用 Image.network() 构造函数来处理来自 URL 的图片。

Image.network('https://picsum.photos/250?image=9'),

4、占位符和网络图片淡入

1、从内存加载占位符

import 'package:flutter/material.dart';
import 'package:transparent_image/transparent_image.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    const title = 'Fade in images';

    return MaterialApp(
      title: title,
      home: Scaffold(
        appBar: AppBar(title: const Text(title)),
        body: Stack(
          children: <Widget>[
            const Center(child: CircularProgressIndicator()),
            Center(
              child: FadeInImage.memoryNetwork(
                placeholder: kTransparentImage,
                image: 'https://picsum.photos/250?image=9',
              ),
            ),
          ],
        ),
      ),
    );
  }
}

2、从本地存储加载占位符

import 'package:flutter/material.dart';
import 'package:transparent_image/transparent_image.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    const title = 'Fade in images';

    return MaterialApp(
      title: title,
      home: Scaffold(
        appBar: AppBar(title: const Text(title)),
        body: Stack(
          children: <Widget>[
            const Center(child: CircularProgressIndicator()),
            Center(
              child: FadeInImage.memoryNetwork(
                placeholder: kTransparentImage,
                image: 'https://picsum.photos/250?image=9',
              ),
            ),
          ],
        ),
      ),
    );
  }
}

5、视频的播放和暂停

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:video_player/video_player.dart';

void main() => runApp(const VideoPlayerApp());

class VideoPlayerApp extends StatelessWidget {
  const VideoPlayerApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Video Player Demo',
      home: VideoPlayerScreen(),
    );
  }
}

class VideoPlayerScreen extends StatefulWidget {
  const VideoPlayerScreen({super.key});

  @override
  State<VideoPlayerScreen> createState() => _VideoPlayerScreenState();
}

class _VideoPlayerScreenState extends State<VideoPlayerScreen> {
  late VideoPlayerController _controller;
  late Future<void> _initializeVideoPlayerFuture;

  @override
  void initState() {
    super.initState();

    // Create and store the VideoPlayerController. The VideoPlayerController
    // offers several different constructors to play videos from assets, files,
    // or the internet.
    _controller = VideoPlayerController.networkUrl(
      Uri.parse(
        'https://flutter.github.io/assets-for-api-docs/assets/videos/butterfly.mp4',
      ),
    );

    // Initialize the controller and store the Future for later use.
    _initializeVideoPlayerFuture = _controller.initialize();

    // Use the controller to loop the video.
    _controller.setLooping(true);
  }

  @override
  void dispose() {
    // Ensure disposing of the VideoPlayerController to free up resources.
    _controller.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Butterfly Video')),
      // Use a FutureBuilder to display a loading spinner while waiting for the
      // VideoPlayerController to finish initializing.
      body: FutureBuilder(
        future: _initializeVideoPlayerFuture,
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            // If the VideoPlayerController has finished initialization, use
            // the data it provides to limit the aspect ratio of the video.
            return AspectRatio(
              aspectRatio: _controller.value.aspectRatio,
              // Use the VideoPlayer widget to display the video.
              child: VideoPlayer(_controller),
            );
          } else {
            // If the VideoPlayerController is still initializing, show a
            // loading spinner.
            return const Center(child: CircularProgressIndicator());
          }
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          // Wrap the play or pause in a call to `setState`. This ensures the
          // correct icon is shown.
          setState(() {
            // If the video is playing, pause it.
            if (_controller.value.isPlaying) {
              _controller.pause();
            } else {
              // If the video is paused, play it.
              _controller.play();
            }
          });
        },
        // Display the correct icon depending on the state of the player.
        child: Icon(
          _controller.value.isPlaying ? Icons.pause : Icons.play_arrow,
        ),
      ),
    );
  }
}