Multidex详解
2024-05-14 02:49:05
Multidex详解
1.使用
1.在项目gralde配置中增加依赖 compile "com.android.support:multidex:1.0.2"
2.在AndroidManifest.xml中声明 application为MultiDexApplication,或者在自定义的application中,重写如下方法protected void attachBaseContext(Context base) {super.attachBaseContext(base);android.support.multidex.MultiDex.install(this);}2.源码详解
public static void install(Context context) {Log.i("MultiDex", "Installing application");if(IS_VM_MULTIDEX_CAPABLE) {// vm支持的不需要使用multidex库Log.i("MultiDex", "VM has multidex support, MultiDex support library is disabled.");} else if(VERSION.SDK_INT < 4) {// 太早Android版本不支持的throw new RuntimeException("MultiDex installation failed. SDK " + VERSION.SDK_INT + " is unsupported. Min SDK version is " + 4 + ".");} else {try {//获取安装的apk的信息ApplicationInfo applicationInfo = getApplicationInfo(context);if(applicationInfo == null) {Log.i("MultiDex", "No ApplicationInfo available, i.e. running on a test Context: MultiDex support library is disabled.");return;}// 开始执行加载其他dex, 加载到data/data/包名/code_cache/secondary-dexes/doInstallation(context, new File(applicationInfo.sourceDir), new File(applicationInfo.dataDir), "secondary-dexes", "");} catch (Exception var2) {Log.e("MultiDex", "MultiDex installation failure", var2);throw new RuntimeException("MultiDex installation failed (" + var2.getMessage() + ").");}Log.i("MultiDex", "install done");}}private static void doInstallation(Context mainContext, File sourceApk, File dataDir, String secondaryFolderName, String prefsKeyPrefix) throws IOException, IllegalArgumentException, IllegalAccessException, NoSuchFieldException, InvocationTargetException, NoSuchMethodException {Set var5 = installedApk;// 已经加载不再重新加载synchronized(installedApk) {if(!installedApk.contains(sourceApk)) {installedApk.add(sourceApk);....ClassLoader loader;try {loader = mainContext.getClassLoader();} catch (RuntimeException var11) {Log.w("MultiDex", "Failure while trying to obtain Context class loader. Must be running in test mode. Skip patching.", var11);return;}if(loader == null) {Log.e("MultiDex", "Context class loader is null. Must be running in test mode. Skip patching.");} else {try {clearOldDexDir(mainContext);} catch (Throwable var10) {Log.w("MultiDex", "Something went wrong when trying to clear old MultiDex extraction, continuing without cleaning.", var10);}// 获取存放目录File dexDir = getDexDir(mainContext, dataDir, secondaryFolderName);// 加载dexList<? extends File> files = MultiDexExtractor.load(mainContext, sourceApk, dexDir, prefsKeyPrefix, false);// 合并使用dexinstallSecondaryDexes(loader, dexDir, files);}}}}3.加载过程
static List<? extends File> load(Context context, File sourceApk, File dexDir, String prefsKeyPrefix, boolean forceReload) throws IOException {...// 是否强制重新加载或dex文件被修改了, 以apk的最后修改时间和zip的crc来校验apk是否被修改if(!forceReload && !isModified(context, sourceApk, currentCrc, prefsKeyPrefix)) {try {files = loadExistingExtractions(context, sourceApk, dexDir, prefsKeyPrefix);} catch (IOException var21) {Log.w("MultiDex", "Failed to reload existing extracted secondary dex files, falling back to fresh extraction", var21);files = performExtractions(sourceApk, dexDir);putStoredApkInfo(context, prefsKeyPrefix, getTimeStamp(sourceApk), currentCrc, files);}} else {Log.i("MultiDex", "Detected that extraction must be performed.");// 准备dexfiles = performExtractions(sourceApk, dexDir);// 保存dex的信息(最后时间和crc信息)到multidex.version的sp配置中putStoredApkInfo(context, prefsKeyPrefix, getTimeStamp(sourceApk), currentCrc, files);}...}private static List<ExtractedDex> performExtractions(File sourceApk, File dexDir) throws IOException {....int secondaryNumber = 2;// 从apk中找出dex文件for(ZipEntry dexFile = apk.getEntry("classes" + secondaryNumber + ".dex"); dexFile != null; dexFile = apk.getEntry("classes" +secondaryNumber + ".dex")) {String fileName = extractedFilePrefix + secondaryNumber + ".zip";// 创建dex对应的zip文件ExtractedDex extractedFile = new ExtractedDex(dexDir, fileName);files.add(extractedFile);Log.i("MultiDex", "Extraction is needed for file " + extractedFile);int numAttempts = 0;boolean isExtractionSuccessful = false;while(numAttempts < 3 && !isExtractionSuccessful) {++numAttempts;// 把dex文件提取出来放到对应的zip文件中, 重试3次extract(apk, dexFile, extractedFile, extractedFilePrefix);try {extractedFile.crc = getZipCrc(extractedFile);isExtractionSuccessful = true;} catch (IOException var19) {isExtractionSuccessful = false;Log.w("MultiDex", "Failed to read crc from " + extractedFile.getAbsolutePath(), var19);}Log.i("MultiDex", "Extraction " + (isExtractionSuccessful?"succeeded":"failed") + " - length " + extractedFile.getAbsolutePath() + ": " + extractedFile.length() + " - crc: " + extractedFile.crc);if(!isExtractionSuccessful) {extractedFile.delete();if(extractedFile.exists()) {Log.w("MultiDex", "Failed to delete corrupted secondary dex '" + extractedFile.getPath() + "'");}}}if(!isExtractionSuccessful) {throw new IOException("Could not create zip file " + extractedFile.getAbsolutePath() + " for secondary dex (" + secondaryNumber + ")");}++secondaryNumber;}...}private static void putStoredApkInfo(Context context, String keyPrefix, long timeStamp, long crc, List<ExtractedDex> extractedDexes) {SharedPreferences prefs = getMultiDexPreferences(context);Editor edit = prefs.edit();edit.putLong(keyPrefix + "timestamp", timeStamp);edit.putLong(keyPrefix + "crc", crc);edit.putInt(keyPrefix + "dex.number", extractedDexes.size() + 1);int extractedDexId = 2;for(Iterator var10 = extractedDexes.iterator(); var10.hasNext(); ++extractedDexId) {ExtractedDex dex = (ExtractedDex)var10.next();edit.putLong(keyPrefix + "dex.crc." + extractedDexId, dex.crc);edit.putLong(keyPrefix + "dex.time." + extractedDexId, dex.lastModified());}edit.commit();}4.合并dex
private static void installSecondaryDexes(ClassLoader loader, File dexDir, List<? extends File> files) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException, InvocationTargetException, NoSuchMethodException, IOException {if(!files.isEmpty()) {if(VERSION.SDK_INT >= 19) {V19.install(loader, files, dexDir);} else if(VERSION.SDK_INT >= 14) {V14.install(loader, files, dexDir);} else {V4.install(loader, files);}}}这里先说明下原理://dalvik.system.DexPathList android遍历dexElements的来加载类的, 所以只要把dex的dexElements合并到apk的pathClassLoade的dexElements中就可以加载到dex中的类public Class findClass(String name, List<Throwable> suppressed) {for (Element element : dexElements) {DexFile dex = element.dexFile;if (dex != null) {Class clazz = dex.loadClassBinaryName(name, definingContext, suppressed);if (clazz != null) {return clazz;}}}if (dexElementsSuppressedExceptions != null) {suppressed.addAll(Arrays.asList(dexElementsSuppressedExceptions));}return null;}private static final class V19 {private V19() {}private static void install(ClassLoader loader, List<? extends File> additionalClassPathEntries, File optimizedDirectory) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException, InvocationTargetException, NoSuchMethodException {Field pathListField = MultiDex.findField(loader, "pathList");Object dexPathList = pathListField.get(loader);ArrayList<IOException> suppressedExceptions = new ArrayList();合并dex的dexElements到pathClassLoade的dexElements中, 通过反射实现MultiDex.expandFieldArray(dexPathList, "dexElements", makeDexElements(dexPathList, new ArrayList(additionalClassPathEntries), optimizedDirectory, suppressedExceptions));...}// 构建dex的DexElements, 在Android6.0之后的DexPathList没有makeDexElements这个方法, 这就是前面判断vm自身支持multidex,不需要再使用multidex库了private static Object[] makeDexElements(Object dexPathList, ArrayList<File> files, File optimizedDirectory, ArrayList<IOException> suppressedExceptions) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {Method makeDexElements = MultiDex.findMethod(dexPathList, "makeDexElements", new Class[]{ArrayList.class, File.class, ArrayList.class});return (Object[])((Object[])makeDexElements.invoke(dexPathList, new Object[]{files, optimizedDirectory, suppressedExceptions}));}}
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