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Flutter 59: 图解 Android Native 获取 Flutter 资源文件

2019-09-01 19热度

      小菜前段时间研究了 Android NativeFlutter 之间的交互;若两端均需要相同资源文件,若不能共享则势必会增加整体包大小;今天和尚研究一下如何通过 Android Native 获取 Flutter 中资源文件;

      官网对于 assets 介绍很简洁,使用过程代码量也很少,虽简洁但依然值得研究;小菜以 Android 为主工程,Flutter 作为 Module 进行测试;

FlutterView

      小菜在学习 AndroidFlutter 交互时会用到 FlutterView 作为桥接控件;而对于资源文件的获取也同样适用;其核心方法是 getLookupKeyForAsset

源码分析

      逐层分析源码,通过 getLookupKeyForAsset 方法我们可以获取资源文件的路径,根目录是固定的 flutter_assets 而非 Module 名;

public String getLookupKeyForAsset(String asset) { return FlutterMain.getLookupKeyForAsset(asset); } public static String getLookupKeyForAsset(String asset) { return fromFlutterAssets(asset); } private static String fromFlutterAssets(String filePath) { return sFlutterAssetsDir + File.separator + filePath; } private static String sFlutterAssetsDir = "flutter_assets";

案例测试

      小菜通过 getLookupKeyForAsset 获取文件路径,以 images/ic_launcher.png 图片为例,借助 assetManager.open 转为流信息转为 Bitmap 进行展示;

// 文件路径:flutter_assets/images/ic_launcher.png try { AssetManager assetManager = getAssets(); InputStream is = assetManager.open(flutterView.getLookupKeyForAsset("images/ic_launcher.png")); Bitmap bitmap = BitmapFactory.decodeStream(is); flutterIv.setImageBitmap(bitmap); } catch (Exception e) { System.out.println("异常信息:" + e.toString()); }

      小菜测试可以用如下方式获取资源文件路径;

// Activity flutterView.getLookupKeyForAsset("images/ic_launcher.png"); // Fragment (FlutterView) getView().getLookupKeyForAsset("images/ic_launcher.png"); // 通用 FlutterMain.getLookupKeyForAsset("images/ic_launcher.png");

PluginRegistry.Registrar

      另一种常用的方式是以插件方式,Flutter 在使用 AndroidView 方式嵌入 Native ViewAndroid 进行交互时;核心方法同样是 lookupKeyForAsset 获取资源路径,之后便是用原生方法解析 assets 资源文件;

      小菜测试时主要注意两点:

  1. 获取 PluginRegistry.Registrar,不能直接 new 对象,需要注册自定义 Native View
  2. 在获取文件路径后尝试了 AssetFileDescriptor 方式解析数据流,完全可以用于 assetManager.open 方式解析;
// 文件路径:flutter_assets/images/ic_launcher.png // Flutter 端 Container( child: AndroidView( viewType: "com.ace.ace_demo01/method_layout", creationParamsCodec: const StandardMessageCodec(), creationParams: {'method_layout_size': 450}), color: Colors.greenAccent, height: 200.0) // Android 端 final String key = "NMethodLayout"; if (this.hasPlugin(key)) return; PluginRegistry.Registrar registrar = this.registrarFor(key); registrar.platformViewRegistry() .registerViewFactory("com.ace.ace_demo01/method_layout", new NMethodLayoutFactory(registrar.messenger())); try { AssetManager assetManager = registrar.context().getAssets(); String assetKey = registrar.lookupKeyForAsset("images/ic_launcher.png"); AssetFileDescriptor fileDescriptor = assetManager.openFd(assetKey); Bitmap bitmap = BitmapFactory.decodeStream(fileDescriptor.createInputStream()); mIv.setImageBitmap(bitmap); } catch (Exception e) { e.printStackTrace(); }

注意事项

      无论是 FlutterView 还是 PluginRegistry.Registrar 方式均需 lookupKeyForAsset 获取 Flutter 端资源文件路径,且获取类型与原生 assets 中一致;小菜测试获取一个 json 文件进行解析;

final String key = "NMethodLayout"; if (this.hasPlugin(key)) return; PluginRegistry.Registrar registrar = this.registrarFor(key); registrar.platformViewRegistry() .registerViewFactory("com.ace.ace_demo01/method_layout", new NMethodLayoutFactory(registrar.messenger())); try { AssetManager assetManager = registrar.context().getAssets(); Log.e("===getJson===", getJson(registrar.lookupKeyForAsset("images/star.json"))); } catch (Exception e) { e.printStackTrace(); } public String getJson(String fileName) { StringBuilder stringBuilder = new StringBuilder(); try { //获取assets资源管理器 AssetManager assetManager = getAssets(); //通过管理器打开文件并读取 InputStreamReader inputReader = new InputStreamReader( assetManager.open(fileName) ); BufferedReader bufReader = new BufferedReader(inputReader); String line="", result=""; while((line = bufReader.readLine()) != null) result += line; return result; } catch (IOException e) { e.printStackTrace(); } return stringBuilder.toString(); } // ===getJson===: { "stars": [ { "name": "水瓶座", "name_en": "Aquarius" }, { "name": "双鱼座", "name_en": "Pisces" }, { "name": "白羊座", "name_en": "Aries" }, { "name": "金牛座", "name_en": "Taurus" }, { "name": "双子座", "name_en": "Gemini" }, { "name": "巨蟹座", "name_en": "Cancer" }, { "name": "狮子座", "name_en": "Leo" }, { "name": "处女座", "name_en": "Virgo" }, { "name": "天秤座", "name_en": "Libra" }, { "name": "天蝎座", "name_en": "Scorpio" }, { "name": "射手座", "name_en": "Sagittarius" }, { "name": "摩羯座", "name_en": "Capricorn" } ]}


      小菜还未成功尝试 Flutter 获取 Native 的资源文件,依旧是从零探索中;如有错误请多多指导!

来源: 阿策小和尚

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