Flutter 模块动态化初探

dim.red

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:

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 = getFluterBundleVersion(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 getFluterBundleVersion(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

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.
  
• 保留 vm_snapshot_data, vm_snapshot_instr 文件.
• 保留 flutter_bundle_version ,flutter_engine_version,flutter_bridge_version 作用如上.

flutter.gradle 修改

• copy {flutter sdk}\flutter\packages\flutter_tools\gradle\flutter.gradle
• 修改 release 依赖为自定义的 flutter jar.

尾巴

更详情的分析留在后面。