代码：tinker 1.9.14.7
一、Tinker加载资源补丁
TinkerLoader.tryLoadPatchFilesInternal 会执行TinkerResourceLoader.loadTinkerResources，此处开始加载资源补丁
TinkerResourceLoader.java
/**
* Load tinker resources
*/
public static boolean loadTinkerResources(TinkerApplication application, String directory, Intent intentResult) {
if (resPatchInfo == null || resPatchInfo.resArscMd5 == null) {
return true;
}
String resourceString = directory + "/" + RESOURCE_PATH + "/" + RESOURCE_FILE;
File resourceFile = new File(resourceString);
long start = System.currentTimeMillis();
//校验资源补丁包 resources.apk 的 md5 值
if (application.isTinkerLoadVerifyFlag()) {
if (!SharePatchFileUtil.checkResourceArscMd5(resourceFile, resPatchInfo.resArscMd5)) {
Log.e(TAG, "Failed to load resource file, path: " + resourceFile.getPath() + ", expect md5: " + resPatchInfo.resArscMd5);
ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_RESOURCE_MD5_MISMATCH);
return false;
}
Log.i(TAG, "verify resource file:" + resourceFile.getPath() + " md5, use time: " + (System.currentTimeMillis() - start));
}
try {
//加载资源
TinkerResourcePatcher.monkeyPatchExistingResources(application, resourceString);
Log.i(TAG, "monkeyPatchExistingResources resource file:" + resourceString + ", use time: " + (System.currentTimeMillis() - start));
} catch (Throwable e) {
Log.e(TAG, "install resources failed");
//remove patch dex if resource is installed failed
try {
//如果资源补丁加载失败的话，会移除 dex 补丁，因为如果dex补丁代码中有引用到资源的话，会报错
SystemClassLoaderAdder.uninstallPatchDex(application.getClassLoader());
} catch (Throwable throwable) {
Log.e(TAG, "uninstallPatchDex failed", e);
}
intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_EXCEPTION, e);
ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_RESOURCE_LOAD_EXCEPTION);
return false;
}
return true;
}
先校验资源resources.apk 的 md5 值，然后加载资源，加载失败会导致dex补丁也被移除。
TinkerResourcePatcher.java
public static void monkeyPatchExistingResources(Context context, String externalResourceFile) throws Throwable {
if (externalResourceFile == null) {
return;
}
final ApplicationInfo appInfo = context.getApplicationInfo();
final Field[] packagesFields;
//利用 packagesFiled 反射获取 LoadedApk 对象，<27外加resourcePackagesFiled
if (Build.VERSION.SDK_INT < 27) {
packagesFields = new Field[]{packagesFiled, resourcePackagesFiled};
} else {
packagesFields = new Field[]{packagesFiled};
}
for (Field field : packagesFields) {
//value = Map<String, WeakReference<LoadedApk>>
final Object value = field.get(currentActivityThread);
for (Map.Entry<String, WeakReference<?>> entry
: ((Map<String, WeakReference<?>>) value).entrySet()) {
final Object loadedApk = entry.getValue().get();
if (loadedApk == null) {
continue;
}
//从 LoadedApk 对象中获取 mResDir 属性, 即资源文件路径
final String resDirPath = (String) resDir.get(loadedApk);
Log.i(TAG, "resDirPath :" + resDirPath);
if (appInfo.sourceDir.equals(resDirPath)) {
//将修复资源放入资源文件路径
resDir.set(loadedApk, externalResourceFile);
}
}
}
//创建一个新的 AssetManager 实例，并把资源补丁apk加载进 AssetManager 中
// Create a new AssetManager instance and point it to the resources installed under
if (((Integer) addAssetPathMethod.invoke(newAssetManager, externalResourceFile)) == 0) {
throw new IllegalStateException("Could not create new AssetManager");
}
// Add SharedLibraries to AssetManager for resolve system resources not found issue
// This influence SharedLibrary Package ID
if (shouldAddSharedLibraryAssets(appInfo)) {
for (String sharedLibrary : appInfo.sharedLibraryFiles) {
if (!sharedLibrary.endsWith(".apk")) {
continue;
}
if (((Integer) addAssetPathAsSharedLibraryMethod.invoke(newAssetManager, sharedLibrary)) == 0) {
throw new IllegalStateException("AssetManager add SharedLibrary Fail");
}
Log.i(TAG, "addAssetPathAsSharedLibrary " + sharedLibrary);
}
}
// Kitkat needs this method call, Lollipop doesn't. However, it doesn't seem to cause any harm
// in L, so we do it unconditionally.
/// 创建出 AssetManager 后，调用 ensureStringBlocks 来确保资源的字符串索引创建出来
if (stringBlocksField != null && ensureStringBlocksMethod != null) {
stringBlocksField.set(newAssetManager, null);
ensureStringBlocksMethod.invoke(newAssetManager);
}
for (WeakReference<Resources> wr : references) {
final Resources resources = wr.get();
if (resources == null) {
continue;
}
// Set the AssetManager of the Resources instance to our brand new one
try {
//pre-N 把原来 resources 的 mAssets 属性替换成新的 AssetManager 对象
assetsFiled.set(resources, newAssetManager);
} catch (Throwable ignore) {
// N之后 mAssets 属性被放在了 ResourcesImpl 中 所以需要先获取 ResourcesImpl 对象再进行替换
final Object resourceImpl = resourcesImplFiled.get(resources);
// for Huawei HwResourcesImpl
final Field implAssets = findField(resourceImpl, "mAssets");
implAssets.set(resourceImpl, newAssetManager);
}
//在 Resource 中会维护一个 mTypedArrayPool 资源池,来减少频繁访问 AssetManager ，所以需要去释放这个资源池，否则取到的都是缓存
clearPreloadTypedArrayIssue(resources);
// 最后调用 updateConfiguration 方法来确保资源更新了
resources.updateConfiguration(resources.getConfiguration(), resources.getDisplayMetrics());
}
// Handle issues caused by WebView on Android N.
// Issue: On Android N, if an activity contains a webview, when screen rotates
// our resource patch may lost effects.
// for 5.x/6.x, we found Couldn't expand RemoteView for StatusBarNotification Exception
if (Build.VERSION.SDK_INT >= 24) {
try {
if (publicSourceDirField != null) {
publicSourceDirField.set(context.getApplicationInfo(), externalResourceFile);
}
} catch (Throwable ignore) {
// Ignored.
}
}
if (!checkResUpdate(context)) {
throw new TinkerRuntimeException(ShareConstants.CHECK_RES_INSTALL_FAIL);
}
}
二、资源加载原理
2.1 apk资源相关内容
apk包中与资源相关的文件：
- assets 存放不参与编译的原始文件资源
- res 存放资源文件，所有文件都被映射到R文件，生成对应资源id。
- resources.arsc 它记录了资源文件，资源文件位置(各个维度的路径)和资源 id 的映射关系等。
2.2 资源加载流程
资源加载是指apk内部assets，res目录下的资源，通过Resources来获取的过程。
类关系
获取流程：
Resource通过代理ResourceImpl来处理，ResourceImpl先尝试从缓存获取，没有缓存在通过AssetManager获取，AssetManager通过addAssetPath来加载apk资源，而具体实现是在native做的。
三、资源补丁修复原理
从前面分析的tinker加载资源补丁流程看主要做了两件事：
- 替换LoadedApk对应的mResDir指向补丁包。
- ResourcesImpl mAssets替换为新的AssetManager，并用新AssetManager调用其addAssetPath加载补丁包。
3.1替换LoadedApk对应的mResDir指向补丁包
LoadedApk是 APK文件信息封装对象。它在ActivityThread启动过程中被初始化，参与Apk加载过程。
ActivityThread.java
final ArrayMap<String, WeakReference<LoadedApk>> mPackages = new ArrayMap<>();
ActivityThread对各包维护了一个map,key=packageName,value=LoadedApk
LoadedApk.java
mResDir 指向资源文件对应的apk路径
那么直接通过反射到map中拿到包名对应的LoadedApk，然后获取属性mResDir，执行补丁包路径。
3.2 ResourcesImpl mAssets替换为新的AssetManager，并用新AssetManager调用其addAssetPath加载补丁包。
低版本mAssets在Resources中，这里代码有兼容。
ResourcesImpl.java
final AssetManager mAssets;
addAssetPath调用栈：
AssetManager.java
.addAssetPath(patchApkPath)
. addAssetPathInternal
.addAssetPathNative
| jni
android_util_AssetManager.cpp::android_content_AssetManager_addAssetPath
AssetManager::addAssetPath
最终将资源路径存放在一个Vector集合中：Vector<asset_path> mAssetPaths
参考：
https://segmentfault.com/a/1190000014016431
https://www.pianshen.com/article/9605795546/
网友评论