Flutter 动态化初探

简介

Flutter : Flutter allows you to build beautiful native apps on iOS and Android from a single codebase. 具有跨平台, 高性能的优势.

Flutter 产物

产物流向:

产物流向

通过分析我们可以发现
不变的产物有 flutter.jar ,libfluter.so,icudtl.dat, vm_snapshot_data , vm_snapshot_instr, 不跟业务代码相关, 只跟 flutter engine 的版本有关.

变化的产物: flutter_assets , isolate_snapshot_data , isolate_snapshot_instr 主要是业务的代码和资源.
LICENSE 没用, 可以删除.
总结:
我们通过将不变的产物集成到APK 中.将变化组成一个资源包,通过配置下发下来.

动态化改造

Flutter SDK 改造

修改 Flutter.createView() 方法.

  @NonNull
    public static FlutterView createView(@NonNull final Context activity, @NonNull final Lifecycle lifecycle,
                                         final String initialRoute, String bundlePath) {
        Context context = activity;
        if (!TextUtils.isEmpty(bundlePath)) {
            final AssetManager bundleAsset = AssetManagerUtils.newAssetManager(bundlePath); //  Flutter  组件资源包位置
            context = new ContextWrapper(activity) {
                @Override
                public Resources getResources() {
                    return new Resources(bundleAsset,
                            super.getResources().getDisplayMetrics(), super.getResources().getConfiguration()) {
                    };
                }
            };
        }

        FlutterMain.startInitialization(context); // 使用自定义的 context 
        FlutterMain.ensureInitializationComplete(activity.getApplicationContext(), null);
        final FlutterNativeView nativeView = new FlutterNativeView(context);// 使用自定义的 context 
      ...
        return flutterView;
    }

这里: 通过反射 AssetManger . 同时将 bundlePath 添加进去.
bundlePath 的作用:

用于查找 flutter_assets, bundleAsset 会在 FlutterNativeView.nativeRunBundleAndSnapshotFromLibrary()传递给 Flutter 用于查找 flutter_assets 资源.
用于 copy isolate_snapshot_data , isolate_snapshot_instr 资源.

Copy 资源是由 ResourceExtractor 完成的.
我们需要修改 ResourceExtractor.ExtractTask

   private void extractResources() {
            final File dataDir = new File(PathUtils.getDataDirectory(mContext));
            final AssetManager bundleManger = mContext.getResources().getAssets();
            //获取 Apk 自身的 AssetsManger
            final AssetManager shareManager = mContext.getApplicationContext().getResources().getAssets();
            final String fluterBundleVersion = getFlutterBundleVersion(bundleManger);
            if (fluterBundleVersion != null) {
                Log.i(TAG, "delete cache fluterBundleVersion " + fluterBundleVersion);
                deleteFiles();
            }
            AssetManager manager;
            byte[] buffer = null;
            for (String asset : mResources) {
                try {
                    final File output = new File(dataDir, asset);

                    if (output.exists()) {
                        continue;
                    }
                    if (output.getParentFile() != null) {
                        output.getParentFile().mkdirs();
                    }

                    manager = bundleManger;
                    if (asset.startsWith("flutter_shared")
                            || asset.equals("vm_snapshot_data")
                            || asset.equals("vm_snapshot_instr")) {
                        manager = shareManager;
                    }
                    ...
                    }
                } catch (FileNotFoundException fnfe) {

                    continue;
                } catch (IOException ioe) {
                    Log.w(TAG, "Exception unpacking resources: " + ioe.getMessage());
                    deleteFiles();
                    return;
                }
            }

            if (fluterBundleVersion != null) {
                try {
                    new File(dataDir, fluterBundleVersion).createNewFile();
                } catch (IOException e) {
                    Log.w(TAG, "Failed to write resource timestamp");
                }
            }
        }

        private String getFlutterBundleVersion(AssetManager bundleAssets) {
            final File dataDir = new File(PathUtils.getDataDirectory(mContext));
            String expectedTimestamp = null;
            try {
                InputStream in = bundleAssets.open("flutter_bundle_version");
                expectedTimestamp = VERSION_PREFIX + IoUtils.toString(in);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (expectedTimestamp == null) {
                return null;
            }
            final String[] existingTimestamps = getVersionStamps(dataDir);

            if (existingTimestamps == null) {
                return null;
            }

            if (existingTimestamps.length != 1
                    || !expectedTimestamp.equals(existingTimestamps[0])) {
                return expectedTimestamp;
            }

            return null;
        }

主要的修改:

共享的资源由 APK 的 AssetsManger 中获取. 其他由 bundleManger 中获取
修改 ResourceExtractor 更新资源逻辑, 由本来的 res_timestamp- {versionCode} -{packageInfo.lastUpdateTime} 不同就更新改为 flutter_bundle_version 不同就更新.

打包插件修改:

组件资源插件

image.png

需要做的事情:

需要组合成一个APK, 因为需要被 AssetManger 识别.
不需要包含代码,
android 资源尽可能少, 但是需要 AndroidManifest.xml
flutter_bundle_version. 每次编译都应不同, 用于 ResourceExtractor 更新版本逻辑.
flutter_engine_version 获取 flutter sdk 版本, 相同版本才能升级, 防止因为版本实现不同导致的 bug.
flutter_bridge_version 是一个 md5. 是对所有自定义的 MethodChannel.MethodCallHandler 进行 ABI 格式化. 即 APK 具有一样的扩展能力.相同版本才能升级.
保留 isolate_snapshot_data, isolate_snapshot_instr 文件.

lib 插件

Flutter 模块一般情况我们是以 aar 的形式依赖. 需要修改上传到 maven 的AAR 如下.