前言：如果程序想要知道有activity启动，如果想要拦截activity，然后跳转到指定的activity怎么办？
我们看下ActivityThread 里面：
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
Context.CONTEXT_INCLUDE_CODE);
}
ComponentName component = r.intent.getComponent();
if (component == null) {
component = r.intent.resolveActivity(
mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}
if (r.activityInfo.targetActivity != null) {
component = new ComponentName(r.activityInfo.packageName,
r.activityInfo.targetActivity);
}
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
try {
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to instantiate activity " + component
+ ": " + e.toString(), e);
}
}
....
if (activity != null) {
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mCompatConfiguration);
if (r.overrideConfig != null) {
config.updateFrom(r.overrideConfig);
}
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
+ r.activityInfo.name + " with config " + config);
Window window = null;
if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
window = r.mPendingRemoveWindow;
r.mPendingRemoveWindow = null;
r.mPendingRemoveWindowManager = null;
}
appContext.setOuterContext(activity);
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback);
if (customIntent != null) {
activity.mIntent = customIntent;
}
可以看到，执行启动activity的时候，
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
那么我们是不是可以在这个时候拦截一下返回的activity呢？
OK,我们继承Instrumentation，并且重写里面的方法。
package com.****r.app;
import android.app.Activity;
import android.app.Instrumentation;
import android.content.Intent;
import com.*****.ActivityAbout;
/**
* =======================================================================================
* 作 者：caoxinyu
* 创建日期：2019/2/19.
* 类的作用:
* 修订历史：
* =======================================================================================
*/
public class MyInstrumentation extends Instrumentation {
private Instrumentation base;
public MyInstrumentation(Instrumentation base) {
this.base = base;
}
@Override
public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException, IllegalAccessException, ClassNotFoundException {
try {
//这里需要setExtrasClassLoader 不然的话，getParecleable 对象可能会拿不到
//很多hook Instrumentation的人都不知道。
// 这里try catch 是防止恶意攻击 导致android.os.BadParcelableException: ClassNotFoundException when unmarshalling
intent.setExtrasClassLoader(cl);
intent.getBooleanExtra("a",false);
}catch (Exception e){
}
if (intent.getBooleanExtra("ActivityAbout",false)) {
return super.newActivity(cl, ActivityAbout.class.getName(), intent);
}
return super.newActivity(cl,className, intent);
}
}
那么怎么使我们重写的类生效呢？
package com.***;
import android.app.Instrumentation;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Hooker {
private static final String TAG = "Hooker";
public static void hookInstrumentation() {
Class<?> activityThread = null;
try {
activityThread = Class.forName("android.app.ActivityThread");
Method sCurrentActivityThread = activityThread.getDeclaredMethod("currentActivityThread");
sCurrentActivityThread.setAccessible(true);
//获取ActivityThread 对象
Object activityThreadObject = sCurrentActivityThread.invoke(activityThread);
//获取 Instrumentation 对象
Field mInstrumentation = activityThread.getDeclaredField("mInstrumentation");
mInstrumentation.setAccessible(true);
Instrumentation instrumentation = (Instrumentation) mInstrumentation.get(activityThreadObject);
MyInstrumentation customInstrumentation = new MyInstrumentation(instrumentation);
//将我们的 customInstrumentation 设置进去
mInstrumentation.set(activityThreadObject, customInstrumentation);
} catch (Exception e) {
e.printStackTrace();
}
}
}
上面这些代码是通过反射，把自己的Instrumentation 设置进去。
然后在程序初始化的时候，调用下面的代码即可。
Hooker.hookInstrumentation();
我们启动一个A activity，如果intent.getBooleanExtra(“ActivityAbout”,false)，那么你的A activity 将被拦截成ActivityAbout。
那么还有一个问题，为什么要设置ClassLoader?
intent.setExtrasClassLoader(cl);
因为如果不设置的话，getParecleable 对象可能会拿不到。在8.0以前的手机，直接崩溃：android.os.BadParcelableException: ClassNotFoundException when unmarshalling。在8.0以上的话，系统会catch 住这个崩溃，但是你的数据全都会被清空。
具体分析如下：
简单try catch，在低版本上没有问题。但是在android8.0以上，会有问题。
在Android8.0以上，如果getBooleanExt 方法里面失败了，系统会catch BadParcelableException，并把intent 里面的数据清空。具体可见下面的截图，
这就导致简单try catch 之后的代码，运行在8.0以上手机，收不到intent里面的数据，因为Intent 里面的跳转数据被清空了。
还是要查清楚为什么会出现ClassNotFoundException when unmarshalling
根据源码，在这里getBooleanExt 会出问题是因为系统在这一步还没有设置解析Parcelable 的classLoader。如下图
所以，有问题的代码需要这样改下。
系统是在调用了 mInstrumentation.newActivity之后设置了classLoader r.intent.setExtrasClassLoader(cl), 所以hook 在newActivity 这一步get Parcelable 数据是有问题的。
不然会有下面这种错误：
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.aaa./.WelcomeActivity}: android.os.BadParcelableException: ClassNotFoundException when unmarshalling: com.nearme.mcs.entity.MessageEntity
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2492)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2678)
at android.app.ActivityThread.access$900(ActivityThread.java:187)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1523)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:210)
at android.app.ActivityThread.main(ActivityThread.java:5809)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1113)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:879)
Caused by: android.os.BadParcelableException: ClassNotFoundException when unmarshalling: com.nearme.mcs.entity.MessageEntity
at android.os.Parcel.readParcelableCreator(Parcel.java:2305)
at android.os.Parcel.readParcelable(Parcel.java:2255)
at android.os.Parcel.readValue(Parcel.java:2162)
at android.os.Parcel.readArrayMapInternal(Parcel.java:2495)
at android.os.BaseBundle.unparcel(BaseBundle.java:221)
at android.os.BaseBundle.getBoolean(BaseBundle.java:658)
at android.content.Intent.getBooleanExtra(Intent.java:5129)
at com.nearme.game.sdk.y.o_a(SourceFile:46)
at com.nearme.game.sdk.y.newActivity(SourceFile:28)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2469)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2678)
at android.app.ActivityThread.access$900(ActivityThread.java:187)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1523)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:210)
at android.app.ActivityThread.main(ActivityThread.java:5809)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1113)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:879)
加油，自己学会了使用Source Insight 看源码。开始慢慢的去学习技术的原理。加油！