Android插件化——资源加载

    public static final int ic_launcher=0x7f060054;
    public static final int ic_launcher_background=0x7f060055;
    public static final int ic_launcher_foreground=0x7f060056;
    public static final int notification_action_background=0x7f060057;

Drawable drawable = resources.getDrawable(resId);

    @Override
    public Resources getResources() {
        return getResourcesInternal();
    }

    private Resources getResourcesInternal() {
        if (mResources == null) {
            if (mOverrideConfiguration == null) {
                mResources = super.getResources();
            } else {
                final Context resContext = createConfigurationContext(mOverrideConfiguration);
                mResources = resContext.getResources();
            }
        }
        return mResources;
    }

    /**
     * Create a new Resources object on top of an existing set of assets in an
     * AssetManager.
     *
     * @param assets Previously created AssetManager.
     * @param metrics Current display metrics to consider when
     *                selecting/computing resource values.
     * @param config Desired device configuration to consider when
     *               selecting/computing resource values (optional).
     */
    public Resources(AssetManager assets, DisplayMetrics metrics, Configuration config) {
        this(null);
        mResourcesImpl = new ResourcesImpl(assets, metrics, config, new DisplayAdjustments());
    }

/**
 * Provides access to an application's raw asset files; see {@link Resources}
 * for the way most applications will want to retrieve their resource data.
 * This class presents a lower-level API that allows you to open and read raw
 * files that have been bundled with the application as a simple stream of
 * bytes.
 */
public final class AssetManager implements AutoCloseable {
...
}

    /**
     * Add an additional set of assets to the asset manager.  This can be
     * either a directory or ZIP file.  Not for use by applications.  Returns
     * the cookie of the added asset, or 0 on failure.
     * {@hide}
     */
    public final int addAssetPath(String path) {
        return  addAssetPathInternal(path, false);
    }

/**
 * 获取对应插件的Resource对象
 * @param context 宿主apk的上下文
 * @param pluginPath 插件apk的路径，带apk名
 * @return
 */
public static Resources getPluginResources(Context context, String pluginPath) {
    try {
        AssetManager assetManager = AssetManager.class.newInstance();
        // 反射调用方法addAssetPath(String path)
        Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);
        // 将插件Apk文件添加进AssetManager
        addAssetPath.invoke(assetManager, pluginPath);
        // 获取宿主apk的Resources对象
        Resources superRes = context.getResources();
        // 获取插件apk的Resources对象
        Resources mResources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());
        return mResources;
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

Drawable drawable = resources.getDrawable(resId);

    /**
     * 加载apk获得内部资源id
     *
     * @param context 宿主上下文
     * @param pluginPath apk路径
     */
    public static int getResId(Context context, String pluginPath, String apkPackageName, String resName) {
        try {
            //在应用安装目录下创建一个名为app_dex文件夹目录,如果已经存在则不创建
            File optimizedDirectoryFile = context.getDir("dex", Context.MODE_PRIVATE);
            // 构建插件的DexClassLoader类加载器，参数：
            // 1、包含dex的apk文件或jar文件的路径，
            // 2、apk、jar解压缩生成dex存储的目录，
            // 3、本地library库目录，一般为null，
            // 4、父ClassLoader
            DexClassLoader dexClassLoader = new DexClassLoader(pluginPath, optimizedDirectoryFile.getPath(), null, ClassLoader.getSystemClassLoader());
            //通过使用apk自己的类加载器，反射出R类中相应的内部类进而获取我们需要的资源id
            Class<?> clazz = dexClassLoader.loadClass(apkPackageName + ".R$drawable");
            Field field = clazz.getDeclaredField(resName);//得到名为resName的这张图片字段
            return field.getInt(R.id.class);//得到图片id
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 0;
    }

                    int resId = getResId(MainActivity.this.getApplication(), PATH, PLUGIN_PACKAGE_NAME, "ic_launcher");
                    Resources resources = getPluginResources(MainActivity.this.getApplication(), PATH);
                    Drawable drawable = resources.getDrawable(resId);
                    mIvTest.setImageDrawable(drawable);