Removal of AssetManifest.json

Flutter apps included an asset file named AssetManifest.json. This file effectively contains a list of assets. Application code can read it using the AssetBundle API to determine what assets are available at runtime.

The AssetManifest.json file is an undocumented implementation detail. It's no longer used by the framework, and it's planned to no longer generate it in a future release of Flutter. If your app's code needs to get a list of available assets, use the AssetManifest API instead.

Before:

import 'dart:convert';
import 'package:flutter/services.dart';

void readAssetList() async {
  final assetManifestContent = await rootBundle.loadString('AssetManifest.json');
  final decodedAssetManifest =
      json.decode(assetManifestContent) as Map<String, Object?>;
  final assets = decodedAssetManifest.keys.toList().cast<String>();
}

After:

import 'package:flutter/services.dart';

void readAssetList() async {
  final assetManifest = await AssetManifest.loadFromAssetBundle(rootBundle);
  final assets = assetManifest.listAssets();
}

The flutter CLI tool generates a new file, AssetManifest.bin. This replaces AssetManifest.json. This file contains the same information as AssetManifest.json, but in a different format. If you need to read this file from code that isn't part of a Flutter app, and therefore can't use the AssetManifest API, you can still parse the file yourself.

The standard_message_codec package can be used to parse the contents.

import 'dart:io';
import 'dart:typed_data';

import 'package:standard_message_codec/standard_message_codec.dart';

void main() {
  // The path to AssetManifest.bin depends on the target platform.
  final pathToAssetManifest = './build/web/assets/AssetManifest.bin';
  final manifest = File(pathToAssetManifest).readAsBytesSync();
  final decoded = const StandardMessageCodec()
      .decodeMessage(ByteData.sublistView(manifest));
  final assets = decoded.keys.cast<String>().toList();
}

Keep in mind that AssetManifest.bin is an implementation detail of Flutter. Reading this file isn't an officially supported workflow. The contents or format of the file might change in a future Flutter release without an announcement.

AssetManifest.json will no longer be generated starting with the fourth stable release after 3.19 or one year after the release of 3.19, whichever comes later.

Relevant issues:

• When building a Flutter app, the flutter tool generates an AssetManifest.json file that's unused by the framework (Issue #143577)

除非另有说明，本文档之所提及适用于 Flutter 的最新稳定版本，本页面最后更新时间: 2024-12-16。 查看文档源码 或者 为本页面内容提出建议。