Tinker 接入及源码分析(二)

  • 2017-01-07
  • 81,389
  • 3

该系列文章分析基于 Tinker1.7.6 版本

Tinker项目地址:https://github.com/Tencent/tinker

Tinker接入及源码分析(一):简单介绍以及如何接入

Tinker接入及源码分析(二):加载补丁源码分析

Tinker接入及源码分析(三):合成补丁源码分析

上篇文章简单的介绍了Tinker的使用:《Tinker接入及源码分析(一)》

再次推荐大家阅读官方wiki:https://github.com/Tencent/tinker/wiki

上篇文章也提及了Tinker的热修复原理,这里再重复一遍:

先简单的说一下Tinker框架热修复的原理,主要是dex文件的修复,不再涉及资源文件以及so文件的修复,通过对比原dex文件(存在bug)与现dex文件(bug已修复)生成差异包,生成的差异包作为补丁包下发给客户端,客户端做一系列校验之后,将下发的差异包与本应用的dex文件合并成成全量的dex文件,并进行opt优化,在应用重启的时候,会在TinkerApplication中加载优化过的全量dex文件,加载过程与QQ空间热修复方案类似,将dex文件插入到DexPathList 中 dexElements的前面。

下面先从简单的入手,分析补丁文件的加载过程,加载之前我们需要明确目前补丁文件已经push到手机,并且通过校验,使用dexDiff算法合成全量补丁并保存到应用data目录下 /data/data/package_name/tinker/

还记得TinkerApplication 和 DefaultApplicationLike 吗?我们就从应用的入口开始分析:

public class SampleApplication extends TinkerApplication {
    public SampleApplication() {
      super(
        //tinkerFlags, tinker支持的类型,dex,library,还是全部都支持!
        ShareConstants.TINKER_ENABLE_ALL,
        //ApplicationLike的实现类,只能传递字符串 
        "tinker.sample.android.app.SampleApplicationLike",
        //Tinker的加载器,一般来说用默认的即可
        "com.tencent.tinker.loader.TinkerLoader",
        //tinkerLoadVerifyFlag, 运行加载时是否校验dex与,ib与res的Md5
        false);
    }  
}

TinkerApplication.:

/**
     * Hook for sub-classes to run logic after the {@link Application#attachBaseContext} has been
     * called but before the delegate is created. Implementors should be very careful what they do
     * here since {@link android.app.Application#onCreate} will not have yet been called.
     */
    private void onBaseContextAttached(Context base) {
        applicationStartElapsedTime = SystemClock.elapsedRealtime();
        applicationStartMillisTime = System.currentTimeMillis();
        loadTinker();
        ensureDelegate();
        try {
            Method method = ShareReflectUtil.findMethod(delegate, "onBaseContextAttached", Context.class);
            method.invoke(delegate, base);
        } catch (Throwable t) {
            throw new TinkerRuntimeException("onBaseContextAttached method not found", t);
        }
        //reset save mode
        if (useSafeMode) {
            String processName = ShareTinkerInternals.getProcessName(this);
            String preferName = ShareConstants.TINKER_OWN_PREFERENCE_CONFIG + processName;
            SharedPreferences sp = getSharedPreferences(preferName, Context.MODE_PRIVATE);
            sp.edit().putInt(ShareConstants.TINKER_SAFE_MODE_COUNT, 0).commit();
        }
    }

其中loadTinker()方法是通过反射初始化我们之前传过来的com.tencent.tinker.loader.TinkerLoader,并且调用它的tryLoad方法,该方法也是加载补丁包的关键所在,我们先放一放,继续往下看。

ensureDelegate() 方法最终会调用createDelegate(),createDelegate()是通过反射初始化化我们传过来的tinker.sample.android.app.SampleApplicationLike,最后会将初始化好的对象赋值给delegate。

private Object createDelegate() {
        try {
            // Use reflection to create the delegate so it doesn't need to go into the primary dex.
            // And we can also patch it
            Class<?> delegateClass = Class.forName(delegateClassName, false, getClassLoader());
            Constructor<?> constructor = delegateClass.getConstructor(Application.class, int.class, boolean.class, long.class, long.class,
                Intent.class, Resources[].class, ClassLoader[].class, AssetManager[].class);
            return constructor.newInstance(this, tinkerFlags, tinkerLoadVerifyFlag,
                applicationStartElapsedTime, applicationStartMillisTime,
                tinkerResultIntent, resources, classLoader, assetManager);
        } catch (Throwable e) {
            throw new TinkerRuntimeException("createDelegate failed", e);
        }
    }

接下来便是在TinkerApplication各个生命周期方法中通过反射调用代理的ApplicationLike中对应的生命周期方法。比如onBaseContextAttached中的:

try {
    Method method = ShareReflectUtil.findMethod(delegate, "onBaseContextAttached", Context.class);
    method.invoke(delegate, base);
} catch (Throwable t) {
    throw new TinkerRuntimeException("onBaseContextAttached method not found", t);
}

以及其他方法:

 @Override
    public void onCreate() {
        super.onCreate();
        ensureDelegate();
        delegateMethod("onCreate");
    }

    @Override
    public void onTerminate() {
        super.onTerminate();
        delegateMethod("onTerminate");
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        delegateMethod("onLowMemory");
    }

下面主要来看一下加载补丁的方法loadTinker():

private void loadTinker() {
        //disable tinker, not need to install
        if (tinkerFlags == TINKER_DISABLE) {
            return;
        }
        tinkerResultIntent = new Intent();
        try {
            //reflect tinker loader, because loaderClass may be define by user!
            Class<?> tinkerLoadClass = Class.forName(loaderClassName, false, getClassLoader());

            Method loadMethod = tinkerLoadClass.getMethod(TINKER_LOADER_METHOD, TinkerApplication.class, int.class, boolean.class);
            Constructor<?> constructor = tinkerLoadClass.getConstructor();
            tinkerResultIntent = (Intent) loadMethod.invoke(constructor.newInstance(), this, tinkerFlags, tinkerLoadVerifyFlag);
        } catch (Throwable e) {
            //has exception, put exception error code
            ShareIntentUtil.setIntentReturnCode(tinkerResultIntent, ShareConstants.ERROR_LOAD_PATCH_UNKNOWN_EXCEPTION);
            tinkerResultIntent.putExtra(INTENT_PATCH_EXCEPTION, e);
        }
    }

其中loaderClassName是我们传过来的:com.tencent.tinker.loader.TinkerLoader,最终会调用该类的tryLoad方法,下面我们转到TinkerLoader,看tryLoad方法:

/**
     * only main process can handle patch version change or incomplete
     */
    @Override
    public Intent tryLoad(TinkerApplication app, int tinkerFlag, boolean tinkerLoadVerifyFlag) {
        Intent resultIntent = new Intent();

        long begin = SystemClock.elapsedRealtime();
        tryLoadPatchFilesInternal(app, tinkerFlag, tinkerLoadVerifyFlag, resultIntent);
        long cost = SystemClock.elapsedRealtime() - begin;
        ShareIntentUtil.setIntentPatchCostTime(resultIntent, cost);
        return resultIntent;
    }

调用tryLoadPatchFilesInternal,并计算耗时:

private void tryLoadPatchFilesInternal(TinkerApplication app, int tinkerFlag, boolean tinkerLoadVerifyFlag, Intent resultIntent) {
        if (!ShareTinkerInternals.isTinkerEnabled(tinkerFlag)) {
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_DISABLE);
            return;
        }
        //tinker
        File patchDirectoryFile = SharePatchFileUtil.getPatchDirectory(app);
        if (patchDirectoryFile == null) {
            Log.w(TAG, "tryLoadPatchFiles:getPatchDirectory == null");
            //treat as not exist
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_DIRECTORY_NOT_EXIST);
            return;
        }
        String patchDirectoryPath = patchDirectoryFile.getAbsolutePath();

        //check patch directory whether exist
        if (!patchDirectoryFile.exists()) {
           //...
        }

        //tinker/patch.info
        File patchInfoFile = SharePatchFileUtil.getPatchInfoFile(patchDirectoryPath);

        //check patch info file whether exist
        if (!patchInfoFile.exists()) {
            //...
        }
        //old = 641e634c5b8f1649c75caf73794acbdf
        //new = 2c150d8560334966952678930ba67fa8
        File patchInfoLockFile = SharePatchFileUtil.getPatchInfoLockFile(patchDirectoryPath);

        patchInfo = SharePatchInfo.readAndCheckPropertyWithLock(patchInfoFile, patchInfoLockFile);
        if (patchInfo == null) {
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_INFO_CORRUPTED);
            return;
        }

        String oldVersion = patchInfo.oldVersion;
        String newVersion = patchInfo.newVersion;

        if (oldVersion == null || newVersion == null) {
            //it is nice to clean patch
            Log.w(TAG, "tryLoadPatchFiles:onPatchInfoCorrupted");
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_INFO_CORRUPTED);
            return;
        }

        resultIntent.putExtra(ShareIntentUtil.INTENT_PATCH_OLD_VERSION, oldVersion);
        resultIntent.putExtra(ShareIntentUtil.INTENT_PATCH_NEW_VERSION, newVersion);

        boolean mainProcess = ShareTinkerInternals.isInMainProcess(app);
        boolean versionChanged = !(oldVersion.equals(newVersion));

        String version = oldVersion;
        if (versionChanged && mainProcess) {
            version = newVersion;
        }
        if (ShareTinkerInternals.isNullOrNil(version)) {
            Log.w(TAG, "tryLoadPatchFiles:version is blank, wait main process to restart");
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_INFO_BLANK);
            return;
        }

        //patch-641e634c
        String patchName = SharePatchFileUtil.getPatchVersionDirectory(version);
        if (patchName == null) {
            Log.w(TAG, "tryLoadPatchFiles:patchName is null");
            //we may delete patch info file
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_VERSION_DIRECTORY_NOT_EXIST);
            return;
        }
        //tinker/patch.info/patch-641e634c
        String patchVersionDirectory = patchDirectoryPath + "/" + patchName;
        File patchVersionDirectoryFile = new File(patchVersionDirectory);

        if (!patchVersionDirectoryFile.exists()) {
            Log.w(TAG, "tryLoadPatchFiles:onPatchVersionDirectoryNotFound");
            //we may delete patch info file
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_VERSION_DIRECTORY_NOT_EXIST);
            return;
        }

        //tinker/patch.info/patch-641e634c/patch-641e634c.apk
        File patchVersionFile = new File(patchVersionDirectoryFile.getAbsolutePath(), SharePatchFileUtil.getPatchVersionFile(version));

        if (!patchVersionFile.exists()) {
            Log.w(TAG, "tryLoadPatchFiles:onPatchVersionFileNotFound");
            //we may delete patch info file
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_VERSION_FILE_NOT_EXIST);
            return;
        }

        ShareSecurityCheck securityCheck = new ShareSecurityCheck(app);

        int returnCode = ShareTinkerInternals.checkTinkerPackage(app, tinkerFlag, patchVersionFile, securityCheck);
        if (returnCode != ShareConstants.ERROR_PACKAGE_CHECK_OK) {
            Log.w(TAG, "tryLoadPatchFiles:checkTinkerPackage");
            resultIntent.putExtra(ShareIntentUtil.INTENT_PATCH_PACKAGE_PATCH_CHECK, returnCode);
            ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_PATCH_PACKAGE_CHECK_FAIL);
            return;
        }

        resultIntent.putExtra(ShareIntentUtil.INTENT_PATCH_PACKAGE_CONFIG, securityCheck.getPackagePropertiesIfPresent());

        final boolean isEnabledForDex = ShareTinkerInternals.isTinkerEnabledForDex(tinkerFlag);

        if (isEnabledForDex) {
            //tinker/patch.info/patch-641e634c/dex
            boolean dexCheck = TinkerDexLoader.checkComplete(patchVersionDirectory, securityCheck, resultIntent);
            if (!dexCheck) {
                //file not found, do not load patch
                Log.w(TAG, "tryLoadPatchFiles:dex check fail");
                return;
            }
        }

        final boolean isEnabledForNativeLib = ShareTinkerInternals.isTinkerEnabledForNativeLib(tinkerFlag);

        if (isEnabledForNativeLib) {
            //tinker/patch.info/patch-641e634c/lib
            //...
        }

        //check resource
        final boolean isEnabledForResource = ShareTinkerInternals.isTinkerEnabledForResource(tinkerFlag);
        Log.w(TAG, "tryLoadPatchFiles:isEnabledForResource:" + isEnabledForResource);
        if (isEnabledForResource) {
            //...
        }
        //only work for art platform oat
        boolean isSystemOTA = ShareTinkerInternals.isVmArt() && ShareTinkerInternals.isSystemOTA(patchInfo.fingerPrint);

        //we should first try rewrite patch info file, if there is a error, we can't load jar
        if (isSystemOTA
            || (mainProcess && versionChanged)) {
            //...
        }
        if (!checkSafeModeCount(app)) {
            //...
            return;
        }
        //now we can load patch jar
        if (isEnabledForDex) {
            boolean loadTinkerJars = TinkerDexLoader.loadTinkerJars(app, tinkerLoadVerifyFlag, patchVersionDirectory, resultIntent, isSystemOTA);
            if (!loadTinkerJars) {
                Log.w(TAG, "tryLoadPatchFiles:onPatchLoadDexesFail");
                return;
            }
        }

        //now we can load patch resource
        if (isEnabledForResource) {
            //...
        }
        //all is ok!
        ShareIntentUtil.setIntentReturnCode(resultIntent, ShareConstants.ERROR_LOAD_OK);
        Log.i(TAG, "tryLoadPatchFiles: load end, ok!");
        return;
    }

以上代码省略了部分判断补丁文件是否存在,是否有效,以及加载补丁资源文件的方法,主要检查补丁信息中的数据是否有效,校验补丁签名以及tinkerId与基准包是否一致。在校验签名时,为了加速校验速度,Tinker只校验 *_meta.txt文件,然后再根据meta文件中的md5校验其他文件。最后调用

TinkerDexLoader.loadTinkerJars(app, tinkerLoadVerifyFlag, patchVersionDirectory, resultIntent, isSystemOTA);

开始加载补丁文件:

/**
     * Load tinker JARs and add them to
     * the Application ClassLoader.
     *
     * @param application The application.
     */
    @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    public static boolean loadTinkerJars(Application application, boolean tinkerLoadVerifyFlag, String directory, Intent intentResult, boolean isSystemOTA) {
        if (dexList.isEmpty()) {
            Log.w(TAG, "there is no dex to load");
            return true;
        }

        PathClassLoader classLoader = (PathClassLoader) TinkerDexLoader.class.getClassLoader();
        if (classLoader != null) {
            Log.i(TAG, "classloader: " + classLoader.toString());
        } else {
            Log.e(TAG, "classloader is null");
            ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_DEX_CLASSLOADER_NULL);
            return false;
        }
        String dexPath = directory + "/" + DEX_PATH + "/";
        File optimizeDir = new File(directory + "/" + DEX_OPTIMIZE_PATH);
//        Log.i(TAG, "loadTinkerJars: dex path: " + dexPath);
//        Log.i(TAG, "loadTinkerJars: opt path: " + optimizeDir.getAbsolutePath());

        ArrayList<File> legalFiles = new ArrayList<>();

        final boolean isArtPlatForm = ShareTinkerInternals.isVmArt();
        for (ShareDexDiffPatchInfo info : dexList) {
            //for dalvik, ignore art support dex
            if (isJustArtSupportDex(info)) {
                continue;
            }
            String path = dexPath + info.realName;
            File file = new File(path);

            if (tinkerLoadVerifyFlag) {
                //...校验
            }
            legalFiles.add(file);
        }

        if (isSystemOTA) {
            parallelOTAResult = true;
            parallelOTAThrowable = null;
            Log.w(TAG, "systemOTA, try parallel oat dexes!!!!!");

            TinkerParallelDexOptimizer.optimizeAll(
                legalFiles, optimizeDir,
                new TinkerParallelDexOptimizer.ResultCallback() {
                    long start;

                    @Override
                    public void onStart(File dexFile, File optimizedDir) {
                        start = System.currentTimeMillis();
                        Log.i(TAG, "start to optimize dex:" + dexFile.getPath());
                    }

                    @Override
                    public void onSuccess(File dexFile, File optimizedDir) {
                        // Do nothing.
                        Log.i(TAG, "success to optimize dex " + dexFile.getPath() + "use time " + (System.currentTimeMillis() - start));
                    }
                    @Override
                    public void onFailed(File dexFile, File optimizedDir, Throwable thr) {
                        parallelOTAResult = false;
                        parallelOTAThrowable = thr;
                        Log.i(TAG, "fail to optimize dex " + dexFile.getPath() + "use time " + (System.currentTimeMillis() - start));
                    }
                }
            );
            if (!parallelOTAResult) {
                Log.e(TAG, "parallel oat dexes failed");
                intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_EXCEPTION, parallelOTAThrowable);
                ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_PARALLEL_DEX_OPT_EXCEPTION);
                return false;
            }
        }
        try {
            SystemClassLoaderAdder.installDexes(application, classLoader, optimizeDir, legalFiles);
        } catch (Throwable e) {
            Log.e(TAG, "install dexes failed");
//            e.printStackTrace();
            intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_EXCEPTION, e);
            ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_DEX_LOAD_EXCEPTION);
            return false;
        }

        return true;
    }

以上代码根据传过来的tinkerLoadVerifyFlag选项控制是否每次加载都要验证dex的md5值,一般来说不需要,默认也是false,会节省加载时间。

然后根据传过来的isSystemOTA来决定是否OTA((Ahead-Of—Time 提前编译)优化

最后调用

SystemClassLoaderAdder.installDexes(application, classLoader, optimizeDir, legalFiles)

加载dex文件

@SuppressLint("NewApi")
    public static void installDexes(Application application, PathClassLoader loader, File dexOptDir, List<File> files)
        throws Throwable {

        if (!files.isEmpty()) {
            ClassLoader classLoader = loader;
            if (Build.VERSION.SDK_INT >= 24) {
                classLoader = AndroidNClassLoader.inject(loader, application);
            }
            //because in dalvik, if inner class is not the same classloader with it wrapper class.
            //it won't fail at dex2opt
            if (Build.VERSION.SDK_INT >= 23) {
                V23.install(classLoader, files, dexOptDir);
            } else if (Build.VERSION.SDK_INT >= 19) {
                V19.install(classLoader, files, dexOptDir);
            } else if (Build.VERSION.SDK_INT >= 14) {
                V14.install(classLoader, files, dexOptDir);
            } else {
                V4.install(classLoader, files, dexOptDir);
            }
            //install done
            sPatchDexCount = files.size();
            Log.i(TAG, "after loaded classloader: " + classLoader + ", dex size:" + sPatchDexCount);

            if (!checkDexInstall(classLoader)) {
                //reset patch dex
                SystemClassLoaderAdder.uninstallPatchDex(classLoader);
                throw new TinkerRuntimeException(ShareConstants.CHECK_DEX_INSTALL_FAIL);
            }
        }
    }

这里就是根据不同的系统版本把dex插到dexElements的前面,其中比较特殊的是安卓7.0,在Dalvik虚拟机中是通过JIT,在运行时将热代码编译成机器码,可以提高下次运行到这段代码的速度,ART虚拟机改变了这种方式,改为OTA,一开始安装的时候就会将字节码编译成机器码,提高运行效率,但带来了2个问题,一个是安装时间过长,占用体积过大;

所以在Android N上改变了这种激进的编译方式,改为混合编译,混合编译运行主要指AOT编译,解释执行与JIT编译。简单来说,在应用运行时分析运行过的代码以及“热代码”,并将配置存储下来。在设备空闲与充电时,ART仅仅编译这份配置中的“热代码”。

无论是使用插入pathlist还是parent classloader的方式,若补丁修改的class已经存在与app image,它们都是无法通过热补丁更新的。它们在启动app时已经加入到PathClassloader的ClassTable中,系统在查找类时会直接使用base.apk中的class

假设base.art文件在补丁前已经存在,这里存在三种情况:

  1. 补丁修改的类都不app image中;这种情况是最理想的,此时补丁机制依然有效;
  2. 补丁修改的类部分在app image中;这种情况我们只能更新一部分的类,此时是最危险的。一部分类是新的,一部分类是旧的,app可能会出现地址错乱而出现crash。
  3. 补丁修改的类全部在app image中;这种情况只是造成补丁不生效,app并不会因此造成crash。

Tinker的解决方案是,完全废弃掉PathClassloader,而采用一个新建Classloader来加载后续的所有类,即可达到将cache无用化的效果。基本原理我们清楚了,让我们来看下代码吧。

if (Build.VERSION.SDK_INT >= 24) {
    classLoader = AndroidNClassLoader.inject(loader, application);
}

以上关于AndroidN的内容可以参考:Android N混合编译与对热补丁影响解析

继续往下看具体的加载过程,这里就看一个V14的实现吧:

/**
     * Installer for platform versions 14, 15, 16, 17 and 18.
     */
    private static final class V14 {

        private static void install(ClassLoader loader, List<File> additionalClassPathEntries,
                                    File optimizedDirectory)
            throws IllegalArgumentException, IllegalAccessException,
            NoSuchFieldException, InvocationTargetException, NoSuchMethodException {
            /* The patched class loader is expected to be a descendant of
             * dalvik.system.BaseDexClassLoader. We modify its
             * dalvik.system.DexPathList pathList field to append additional DEX
             * file entries.
             */
            Field pathListField = ShareReflectUtil.findField(loader, "pathList");
            Object dexPathList = pathListField.get(loader);
            ShareReflectUtil.expandFieldArray(dexPathList, "dexElements", makeDexElements(dexPathList,
                new ArrayList<File>(additionalClassPathEntries), optimizedDirectory));
        }

        /**
         * A wrapper around
         * {@code private static final dalvik.system.DexPathList#makeDexElements}.
         */
        private static Object[] makeDexElements(
            Object dexPathList, ArrayList<File> files, File optimizedDirectory)
            throws IllegalAccessException, InvocationTargetException,
            NoSuchMethodException {
            Method makeDexElements =
                ShareReflectUtil.findMethod(dexPathList, "makeDexElements", ArrayList.class, File.class);

            return (Object[]) makeDexElements.invoke(dexPathList, files, optimizedDirectory);
        }
    }

通过反射拿到BaseDexClassLoader的pathList,然后通过反射调用PathList的makeDexElements传进去的参数分别是补丁dexList和优化过的opt目录,在Tinker中是dex补丁目录的同级目录odex/。

看一下下面这个方法,是将生成的dexElements插入到原先dexElements的前面。

public static void expandFieldArray(Object instance, String fieldName, Object[] extraElements)
        throws NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
        Field jlrField = findField(instance, fieldName);

        Object[] original = (Object[]) jlrField.get(instance);
        Object[] combined = (Object[]) Array.newInstance(original.getClass().getComponentType(), original.length + extraElements.length);

        // NOTE: changed to copy extraElements first, for patch load first

        System.arraycopy(extraElements, 0, combined, 0, extraElements.length);
        System.arraycopy(original, 0, combined, extraElements.length, original.length);

        jlrField.set(instance, combined);
    }

首先会拿到原始的数组:

Object[] original = (Object[]) jlrField.get(instance);

再生成一个长度为original.length + extraElements.length的新数组,

Object[] combined = (Object[]) Array.newInstance(original.getClass().getComponentType(), original.length + extraElements.length);

然后先把传进来的extraElements拷贝到新数组中,再把原始的数组拷贝进来,这里的位置很重要,必须得得将加载的dex文件列表拷贝到数组前面,再拷贝原先的数组放在数组的后面;否则补丁将不会生效。

System.arraycopy(extraElements, 0, combined, 0, extraElements.length);
System.arraycopy(original, 0, combined, extraElements.length, original.length);

最后将新数组设置进instance中。

jlrField.set(instance, combined);

到此为止加载补丁dex文件的过程就结束了。

至于为什么新的补丁文件加载的类会生效,那么需要看一下BaseDexClassLoader,该类是PathClassLoader和DexClassLoader的基类,

public BaseDexClassLoader(String dexPath, File optimizedDirectory,
            String libraryPath, ClassLoader parent) {
        super(parent);

        this.originalPath = dexPath;
        this.pathList =
            new DexPathList(this, dexPath, libraryPath, optimizedDirectory);
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        Class clazz = pathList.findClass(name);

        if (clazz == null) {
            throw new ClassNotFoundException(name);
        }

        return clazz;
    }

其中findClass会调用DexPathList的findClass:

//DexPathList
    public Class findClass(String name) {
        for (Element element : dexElements) {
            DexFile dex = element.dexFile;

            if (dex != null) {
                Class clazz = dex.loadClassBinaryName(name, definingContext);
                if (clazz != null) {
                    return clazz;
                }
            }
        }
        return null;
    }

从这里便可以看出dexElements中Element元素顺序的作用了,前面的会先被读取到,如果读取到了对应的类循环就会结束。

下篇文章会介绍补丁文件的合成过程,敬请期待…

>> 转载请注明来源:Tinker 接入及源码分析(二)

●非常感谢您的阅读,欢迎订阅微信公众号(右边扫一扫)以表达对我的认可与支持,我会在第一时间同步文章到公众号上。当然也可点击下方打赏按钮为我打赏。

免费分享,随意打赏

感谢打赏!
微信
支付宝

评论

  • w4lle回复

    写的不错,有个问题就是AndroidNClassLoader其实是为了避免AndroidN混合编译对Tinker的影响。可以参考Tinker相关文章

  • pills回复

    We stumbled over here coming from a different website
    and thought I should check things out. I like what I see so now i’m following you.
    Look forward to looking at your web page for a second
    time.

发表评论