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Android中插件化的簡單實現：啟動未注冊的Activity
前言
本文介紹在Android中啟動未在AndroidManifest中注冊的Activity的一個解決方案。主要需要掌握以下知識點：
-
反射
-
類加載
-
Activity的啟動過程
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Resource加載過程
啟動應用內未注冊的Activity
Activity默認都需要在AndroidManifest中注冊，未注冊的應用無法啟動。AMS在啟動應用時，會檢測是否已經注冊。因此，如果想要啟動未注冊的Activity,那么需要在Activity前，替換啟動應用的Intent為已經注冊過的Activity,因此可以新建一個Activity，用於占位。在檢測通過后，真正啟動Activity前再替換回需要啟動的未注冊的Activity。
獲取替換Intent的Hook點
調用startActivity方法后，最后都會在Instrumentation的execStartActivity方法中調用AMS的遠程方法進行處理。Android6.0及以下和Android6.0以上，在execStartActivity中調用AMS的方法有所不同，因此需要做兼容處理。
6.0
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
//...
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
//...
}
通過調用ActivityManagerNative.getDefault()來獲取AMS。
8.0
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
IApplicationThread whoThread = (IApplicationThread) contextThread;
//...
int result = ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
//...
}
通過調用ActivityManager.getService()來獲取AMS。
替換Intent
public static void hookAMS() {
try {
Field singletonField;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
singletonField = getField(Class.forName("android.app.ActivityManager"), "IActivityManagerSingleton");
} else {
singletonField = getField(Class.forName("android.app.ActivityManagerNative"), "gDefault");
}
Object singleton = singletonField.get(null);
Field mInstanceField = getField(Class.forName("android.util.Singleton"), "mInstance");
final Object mInstance = mInstanceField.get(singleton);
final Object proxyInstance = Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), new Class[]{Class.forName("android.app.IActivityManager")}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if ("startActivity".equals(method.getName())) {
int index = 0;
for (int i = 0; i < args.length; i++) {
if (args[i] instanceof Intent) {
index = i;
break;
}
}
Intent intent = (Intent) args[index];
Intent proxyIntent = new Intent(intent);
//占位的Activity
proxyIntent.setClassName("com.wangyz.plugindemo", "com.wangyz.plugindemo.ProxyActivity");
proxyIntent.putExtra("target_intent", intent);
args[index] = proxyIntent;
}
return method.invoke(mInstance, args);
}
});
mInstanceField.set(singleton, proxyInstance);
} catch (Exception e) {
e.printStackTrace();
}
}
獲取還原Intent的Hook點
Android8.0及以下
啟動Activity的消息，會回調到ActivityThread中的mH的dispatchMessage方法，可以通過給mH設置一個callBack,在callBack的handleMessage中，然后替換回真正要啟動的Intent，然后返回false,讓handleMessage再繼續處理。
public void dispatchMessage(Message msg) {
if (msg.callback != null) {
handleCallback(msg);
} else {
if (mCallback != null) {
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);
}
}
Android8.0及以下，在ActivityThread的mH中的handleMessage方法中，會處理LAUNCH_ACTIVITY類型的消息，在這里調用了handleLaunchActivity方法來啟動Activity。
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
final ActivityClientRecord r = (ActivityClientRecord) msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo, r.compatInfo);
handleLaunchActivity(r, null);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
Android9.0
和8.0一樣，設置callBack，然后修改Intent。
在ActivityThread的mH中的handleMessage方法中，會處理EXECUTE_TRANSACTION類型的消息，在這里調用了TransactionExecutor.execute方法
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
if (isSystem()) {
// Client transactions inside system process are recycled on the client side
// instead of ClientLifecycleManager to avoid being cleared before this
// message is handled.
transaction.recycle();
}
// TODO(lifecycler): Recycle locally scheduled transactions.
break;
execute方法中會調用executeCallbacks
public void execute(ClientTransaction transaction) {
final IBinder token = transaction.getActivityToken();
log("Start resolving transaction for client: " + mTransactionHandler + ", token: " + token);
executeCallbacks(transaction);
executeLifecycleState(transaction);
mPendingActions.clear();
log("End resolving transaction");
}
public void executeCallbacks(ClientTransaction transaction) {
final List<ClientTransactionItem> callbacks = transaction.getCallbacks();
if (callbacks == null) {
// No callbacks to execute, return early.
return;
}
log("Resolving callbacks");
final IBinder token = transaction.getActivityToken();
ActivityClientRecord r = mTransactionHandler.getActivityClient(token);
// In case when post-execution state of the last callback matches the final state requested
// for the activity in this transaction, we won't do the last transition here and do it when
// moving to final state instead (because it may contain additional parameters from server).
final ActivityLifecycleItem finalStateRequest = transaction.getLifecycleStateRequest();
final int finalState = finalStateRequest != null ? finalStateRequest.getTargetState()
: UNDEFINED;
// Index of the last callback that requests some post-execution state.
final int lastCallbackRequestingState = lastCallbackRequestingState(transaction);
final int size = callbacks.size();
for (int i = 0; i < size; ++i) {
final ClientTransactionItem item = callbacks.get(i);
log("Resolving callback: " + item);
final int postExecutionState = item.getPostExecutionState();
final int closestPreExecutionState = mHelper.getClosestPreExecutionState(r,
item.getPostExecutionState());
if (closestPreExecutionState != UNDEFINED) {
cycleToPath(r, closestPreExecutionState);
}
item.execute(mTransactionHandler, token, mPendingActions);
item.postExecute(mTransactionHandler, token, mPendingActions);
if (r == null) {
// Launch activity request will create an activity record.
r = mTransactionHandler.getActivityClient(token);
}
if (postExecutionState != UNDEFINED && r != null) {
// Skip the very last transition and perform it by explicit state request instead.
final boolean shouldExcludeLastTransition =
i == lastCallbackRequestingState && finalState == postExecutionState;
cycleToPath(r, postExecutionState, shouldExcludeLastTransition);
}
}
}
這個方法里會調用ClientTransactionItem的execute方法。ClientTransactionItem是在ActivityStackSupervisor中的realStartActivityLocked中添加的
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
// Create activity launch transaction.
final ClientTransaction clientTransaction = ClientTransaction.obtain(app.thread,
r.appToken);
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
// TODO: Have this take the merged configuration instead of separate global
// and override configs.
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
r.persistentState, results, newIntents, mService.isNextTransitionForward(),
profilerInfo));
}
因此，ClientTransactionItem對應的具體類為LaunchActivityItem，它對應的execute方法
@Override
public void execute(ClientTransactionHandler client, IBinder token,
PendingTransactionActions pendingActions) {
Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,
mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,
mPendingResults, mPendingNewIntents, mIsForward,
mProfilerInfo, client);
client.handleLaunchActivity(r, pendingActions, null /* customIntent */);
Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);
}
在它的方法里又調用了ClientTransactionHandler的handleLaunchActivity,而ClientTransactionHandler就是在ActivityThread中定義的
private final TransactionExecutor mTransactionExecutor = new TransactionExecutor(this);
ActivityThread繼承了ClientTransactionHandler，那么它就會實現handleLaunchActivity。最終在這個方法里啟動Activity
public final class ActivityThread extends ClientTransactionHandler {
@Override
public Activity handleLaunchActivity(ActivityClientRecord r,
PendingTransactionActions pendingActions, Intent customIntent) {
}
}
還原Intent
public static void hookHandler() {
try {
Field sCurrentActivityThreadThread = getField(Class.forName("android.app.ActivityThread"), "sCurrentActivityThread");
Object activityThread = sCurrentActivityThreadThread.get(null);
Field mHField = getField(Class.forName("android.app.ActivityThread"), "mH");
Object mH = mHField.get(activityThread);
Field mCallbackField = getField(Class.forName("android.os.Handler"), "mCallback");
mCallbackField.set(mH, new Handler.Callback() {
@Override
public boolean handleMessage(Message msg) {
switch (msg.what) {
case 100: {
try {
Field intentField = getField(msg.obj.getClass(), "intent");
Intent proxyIntent = (Intent) intentField.get(msg.obj);
Intent targetIntent = proxyIntent.getParcelableExtra("target_intent");
if (targetIntent != null) {
// proxyIntent.setComponent(targetIntent.getComponent());
intentField.set(msg.obj, targetIntent);
}
} catch (Exception e) {
e.printStackTrace();
}
}
break;
case 159: {
try {
Field mActivityCallbacksField = getField(msg.obj.getClass(), "mActivityCallbacks");
List mActivityCallbacks = (List) mActivityCallbacksField.get(msg.obj);
for (int i = 0; i < mActivityCallbacks.size(); i++) {
if (mActivityCallbacks.get(i).getClass().getName()
.equals("android.app.servertransaction.LaunchActivityItem")) {
Object launchActivityItem = mActivityCallbacks.get(i);
Field mIntentField = getField(launchActivityItem.getClass(), "mIntent");
Intent intent = (Intent) mIntentField.get(launchActivityItem);
// 獲取插件的
Intent proxyIntent = intent.getParcelableExtra("target_intent");
//替換
if (proxyIntent != null) {
mIntentField.set(launchActivityItem, proxyIntent);
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
break;
default:
break;
}
return false;
}
});
} catch (Exception e) {
e.printStackTrace();
}
}
在Application創建時Hook
@Override
public void onCreate() {
super.onCreate();
//一般是從服務器下載回來，然后復制到應用的私有目錄下，這里演示從sdcard復制到data目錄下,6.0及以上需要申請動態權限。復制應該放在非UI線程上做，這里簡化操作，放在UI線程上操作。
String pluginPath = getDir("plugin", Context.MODE_PRIVATE).getAbsolutePath();
pluginPath = pluginPath + "/plugin.apk";
if (!new File(pluginPath).exists()) {
FileUtil.copyFile(PLUGIN_PATH, pluginPath);
}
HookUtil.loadPlugin(this, pluginPath);
HookUtil.hookAMS();
HookUtil.hookHandler();
}
到這里，就可以啟用同一應用內未注冊的Activity。
啟動插件應用內的Activity
啟動非同一應用內的Activity,相比啟動同一應用內的Activity,需要多幾個步驟。由於不在一個應用內，所以需要把插件的APK先加載進來，然后同樣也需要在AMS檢測前替換Intent為占位的Intent,在檢測后，啟動Activity前替換回為需要啟動Activity的Intent。另外，由於插件是動態加載進去的，也需要解決資源加載的問題。
加載插件
加載插件主要是用到類加載器
public static void loadPlugin(Context context, String dexPath) {
//判斷dex是否存在
File dex = new File(dexPath);
if (!dex.exists()) {
return;
}
try {
//獲取自己的dexElements
PathClassLoader pathClassLoader = (PathClassLoader) context.getClassLoader();
Field pathListField = getField(pathClassLoader.getClass(), "pathList");
Object pathListObject = pathListField.get(pathClassLoader);
Field dexElementsField = getField(pathListObject.getClass(), "dexElements");
Object[] dexElementsObject = (Object[]) dexElementsField.get(pathListObject);
//獲取dex中的dexElements
File odex = context.getDir("odex", Context.MODE_PRIVATE);
DexClassLoader dexClassLoader = new DexClassLoader(dexPath, odex.getAbsolutePath(), null, pathClassLoader);
Field pluginPathListField = getField(dexClassLoader.getClass(), "pathList");
Object pluginPathListObject = pluginPathListField.get(dexClassLoader);
Field pluginDexElementsField = getField(pluginPathListObject.getClass(), "dexElements");
Object[] pluginDexElementsObject = (Object[]) pluginDexElementsField.get(pluginPathListObject);
Class<?> elementClazz = dexElementsObject.getClass().getComponentType();
Object newDexElements = Array.newInstance(elementClazz, pluginDexElementsObject.length + dexElementsObject.length);
System.arraycopy(pluginDexElementsObject, 0, newDexElements, 0, pluginDexElementsObject.length);
System.arraycopy(dexElementsObject, 0, newDexElements, pluginDexElementsObject.length, dexElementsObject.length);
//設置
dexElementsField.set(pathListObject, newDexElements);
} catch (Exception e) {
e.printStackTrace();
}
}
替換Intent
這個過程和應用內的情況是一樣的，不再贅述
加載資源
加載資源主要用到AssetManager的addAssetPath方法，通過反射來加載
private static Resources loadResource(Context context) {
try {
AssetManager assetManager = AssetManager.class.newInstance();
Method addAssetPathField = assetManager.getClass().getDeclaredMethod("addAssetPath", String.class);
addAssetPathField.setAccessible(true);
addAssetPathField.invoke(assetManager, PATH);
Resources resources = context.getResources();
return new Resources(assetManager, resources.getDisplayMetrics(), resources.getConfiguration());
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
源碼
https://github.com/milovetingting/Samples/tree/master/PluginDemo