目前插件化加载插件资源有两种方案：
- 合并式的Resource方案： 将插件资源合并加载到宿主中
- 独立式的Resource方案： 创建插件新的Resource，与宿主隔离
先来了解下，android 7.0 Framework 层中Resource对象的创建过程。
从Activity或者Application获取Resource对象实际上，最终都是通过ContextImpl#getResource()获取的。
getResource():
@Override
public Resources getResources() {
return mResources;
}
检索发现，Resource对象是在构建ContextImpl对象的时候获取到的（第1个的hook点，后续会用到）。
查看构造方法：
private Resources mResources;
private ContextImpl(ContextImpl container, ActivityThread mainThread,
LoadedApk packageInfo, IBinder activityToken, UserHandle user, int flags,
Display display, Configuration overrideConfiguration, int createDisplayWithId) {
mPackageInfo = packageInfo;
//...省略部分源码
Resources resources = packageInfo.getResources(mainThread);
//...省略部分源码
mResources = resources;
}
接下来看下,LoadedApk又是如何创建Resource对象?
getResources():
public Resources getResources(ActivityThread mainThread) {
if (mResources == null) {
mResources = mainThread.getTopLevelResources(mResDir, mSplitResDirs, mOverlayDirs,
mApplicationInfo.sharedLibraryFiles, Display.DEFAULT_DISPLAY, this);
}
return mResources;
}
从上可知LoadedApk中也存在Resource对象（第2个的hook点，后续会用到）。
接下来，继续查看ActivityThread中又是如何创建Resource。
getTopLevelResources():
Resources getTopLevelResources(String resDir, String[] splitResDirs, String[] overlayDirs,
String[] libDirs, int displayId, LoadedApk pkgInfo) {
return mResourcesManager.getResources(null, resDir, splitResDirs, overlayDirs, libDirs,
displayId, null, pkgInfo.getCompatibilityInfo(), pkgInfo.getClassLoader());
}
从ResourceManager中获取，若是为空，则创建新的Resource对象。
getResources():
public @NonNull Resources getResources(@Nullable IBinder activityToken,
@Nullable String resDir,
@Nullable String[] splitResDirs,
@Nullable String[] overlayDirs,
@Nullable String[] libDirs,
int displayId,
@Nullable Configuration overrideConfig,
@NonNull CompatibilityInfo compatInfo,
@Nullable ClassLoader classLoader) {
try {
//存储
final ResourcesKey key = new ResourcesKey(
resDir,
splitResDirs,
overlayDirs,
libDirs,
displayId,
overrideConfig != null ? new Configuration(overrideConfig) : null, // Copy
compatInfo);
classLoader = classLoader != null ? classLoader : ClassLoader.getSystemClassLoader();
return getOrCreateResources(activityToken, key, classLoader);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
}
}
从以上，可以知会创建ResourcesKey对象，用于存储应用程序的信息。用于一个ResourcesKey对一个Resources。
接下来查看getOrCreateResources()
getOrCreateResources():
private @NonNull Resources getOrCreateResources(@Nullable IBinder activityToken,
@NonNull ResourcesKey key, @NonNull ClassLoader classLoader) {
// ... 省略部分源码
//重点在这里,会加载应用程序的资源文件
ResourcesImpl resourcesImpl = createResourcesImpl(key);
synchronized (this) {
ResourcesImpl existingResourcesImpl = findResourcesImplForKeyLocked(key);
if (existingResourcesImpl != null) {
if (DEBUG) {
Slog.d(TAG, "- got beat! existing impl=" + existingResourcesImpl
+ " new impl=" + resourcesImpl);
}
resourcesImpl.getAssets().close();
resourcesImpl = existingResourcesImpl;
} else {
// 将Resources的实现类,和ResourcesKey一对一缓存起来。
mResourceImpls.put(key, new WeakReference<>(resourcesImpl));
}
final Resources resources;
if (activityToken != null) {
resources = getOrCreateResourcesForActivityLocked(activityToken, classLoader,
resourcesImpl);
} else {
//将ResourceImpls作为参数，构建一个新Resources对象
resources = getOrCreateResourcesLocked(classLoader, resourcesImpl);
}
return resources;
}
}
ResourcesImpl是 Resources的实现类，具体加载资源和获取资源信息的操作都在里面。(第3个Hook点，后续会用到)
接下来，查看，如何创建 ResourcesImpl对象。
createResourcesImpl():
private @NonNull ResourcesImpl createResourcesImpl(@NonNull ResourcesKey key) {
final DisplayAdjustments daj = new DisplayAdjustments(key.mOverrideConfiguration);
daj.setCompatibilityInfo(key.mCompatInfo);
//接下来重点,资源文件会被在AssetManager加载。
final AssetManager assets = createAssetManager(key);
final DisplayMetrics dm = getDisplayMetrics(key.mDisplayId, daj);
final Configuration config = generateConfig(key, dm);
final ResourcesImpl impl = new ResourcesImpl(assets, dm, config, daj);
return impl;
}
接下来，查看AssetManager对象的创建过程，如何加载资源文件。
createAssetManager():
protected @NonNull AssetManager createAssetManager(@NonNull final ResourcesKey key) {
AssetManager assets = new AssetManager();
//res资源主目录的路径
if (key.mResDir != null) {
if (assets.addAssetPath(key.mResDir) == 0) {
throw new Resources.NotFoundException("failed to add asset path " + key.mResDir);
}
}
//res资源拼接目录的路径
if (key.mSplitResDirs != null) {
for (final String splitResDir : key.mSplitResDirs) {
if (assets.addAssetPath(splitResDir) == 0) {
throw new Resources.NotFoundException(
"failed to add split asset path " + splitResDir);
}
}
}
//.... 省略部分源码
return assets;
}
从上可知,会通过AssetManager对象的addAssetPath()加载资源文件。
根据一系列的源码追踪了解到，根据资源文件路径，创建AssetManager对象，从而进一步创建Resource对象。
思路：
将插件的资源加载到宿主应用程序中，合并加载到虚拟机中，这样宿主就可以正常访问插件中的资源。
缺点： 存在宿主与插件的资源冲突。
解决方式：通过Android插件化之aapt修改资源前缀
代码实现如下
1. 将插件的资源合并到宿主中,创建新合并后的Resource替换掉宿主原有的Resource对象。
根据源码走向,了解到反射替换宿主原有的Resource对象,有以下若干Hook点:
- ContextImpl 中Resource对象
- LoadedApk中Resource对象
- ResourceManager中resource对象(sdk版本差异处理)
代码如下所示：
private synchronized static void preloadResource(Context context, String apkFilePath) {
try {
// 先创建AssetManager
Class<? extends AssetManager> AssetManagerClass = AssetManager.class;
AssetManager assetManager = AssetManagerClass.newInstance();
// 将插件资源和宿主资源通过 addAssetPath方法添加进去
Method addAssetPathMethod = AssetManagerClass.getDeclaredMethod("addAssetPath", String.class);
addAssetPathMethod.setAccessible(true);
String hostResourcePath = context.getPackageResourcePath();
int result_1 = (int) addAssetPathMethod.invoke(assetManager, hostResourcePath);
int result_2 = (int) addAssetPathMethod.invoke(assetManager, apkFilePath);
// 接下来创建，合并资源后的Resource
Resources resources = new Resources(assetManager, context.getResources().getDisplayMetrics(), context.getResources().getConfiguration());
// 替换 ContextImpl 中Resource对象
Class<?> contextImplClass = context.getClass();
Field resourcesField1 = contextImplClass.getDeclaredField("mResources");
resourcesField1.setAccessible(true);
resourcesField1.set(context, resources);
// 先获取到LoadApk对象
Field loadedApkField = contextImplClass.getDeclaredField("mPackageInfo");
loadedApkField.setAccessible(true);
Object loadApk = loadedApkField.get(context);
Class<?> loadApkClass = loadApk.getClass();
// 替换掉LoadApk中的Resource对象。
Field resourcesField2 = loadApkClass.getDeclaredField("mResources");
resourcesField2.setAccessible(true);
resourcesField2.set(loadApk, resources);
//获取到ActivityThread
Class<?> ActivityThreadClass = Class.forName("android.app.ActivityThread");
Field sCurrentActivityThreadField = ActivityThreadClass.getDeclaredField("sCurrentActivityThread");
sCurrentActivityThreadField.setAccessible(true);
Object ActivityThread = sCurrentActivityThreadField.get(null);
// 获取到ResourceManager对象
Field ResourcesManagerField = ActivityThreadClass.getDeclaredField("mResourcesManager");
ResourcesManagerField.setAccessible(true);
Object resourcesManager = ResourcesManagerField.get(ActivityThread);
// 替换掉ResourceManager中resource对象
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) {
Class<?> resourcesManagerClass = resourcesManager.getClass();
Field mActiveResourcesField = resourcesManagerClass.getDeclaredField("mActiveResources");
mActiveResourcesField.setAccessible(true);
Map<Object, WeakReference<Resources>> map = (Map<Object, WeakReference<Resources>>) mActiveResourcesField.get(resourcesManager);
Object key = map.keySet().iterator().next();
map.put(key, new WeakReference<>(resources));
} else {
// still hook Android N Resources, even though it's unnecessary, then nobody will be strange.
Class<?> resourcesManagerClass = resourcesManager.getClass();
Field mResourceImplsField = resourcesManagerClass.getDeclaredField("mResourceImpls");
mResourceImplsField.setAccessible(true);
Map map = (Map) mResourceImplsField.get(resourcesManager);
Object key = map.keySet().iterator().next();
Field mResourcesImplField = Resources.class.getDeclaredField("mResourcesImpl");
mResourcesImplField.setAccessible(true);
Object resourcesImpl = mResourcesImplField.get(resources);
map.put(key, new WeakReference<>(resourcesImpl));
}
multiResources = resources;
} catch (Exception e) {
e.printStackTrace();
}
}
2. 根据插件中包名、资源目录和文件获取到资源id , 在宿主中加载资源id获取到对应的资源
private void usePluginResource() {
ImageView imageView = findViewById(R.id.main_show_plugin_img_iv);
// 根据包名、资源目录和文件获取到资源id
int imgId=ResourceHookManager.getDrawableId("plugin_img", PluginConfig.package_name);
// 宿主中使用插件的资源id
imageView.setImageDrawable(getResources().getDrawable(imgId));
}
优点：资源不存在冲突，不需要特殊处理。
缺点：存在插件、宿主之间资源信息共享问题。
步骤如下：
- 先根据apk或者zip的路径(包含资源文件)，创建出独立的Resource对象。
public class ResourceHookManager {
private static Resources resources;
public static void init(Context context, String apkFilePath) {
preloadResource(context, apkFilePath);
}
private synchronized static void preloadResource(Context context, String apkFilePath) {
try {
// 先创建AssetManager
AssetManager assetManager = AssetManager.class.newInstance();
AssetManager.class.getDeclaredMethod("addAssetPath", String.class).invoke(
assetManager,apkFilePath);
//在创建Resource
resources=new Resources(assetManager,context.getResources().getDisplayMetrics(), context.getResources().getConfiguration());
} catch (Exception e) {
e.printStackTrace();
}
}
public static Drawable getDrawable(String name,String packageName){
int imgId=getId(name,"mipmap",packageName);
if (imgId==0){
imgId=getId(name,"drawable",packageName);
}
return resources.getDrawable(imgId);
}
public static int getId(String name,String type,String packageName){
return resources.getIdentifier(name,type,packageName);
}
}
- 根据Resouce对象,获取相应的资源:
private void usePluginResource() {
ImageView imageView = findViewById(R.id.main_show_plugin_img_iv);
imageView.setImageDrawable(ResourceHookManager.getDrawable("plugin_img", PluginConfig.package_name));
}