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今天,我们来解决一个问题:
Activity插件化原理第一种方案:Hook Instrumentation
人生一切难题,知识给你答案。
Activity的插件化解决的一个根本性问题就是插件中的Activity并没有在宿主的AndroidManifest.xml中进行注册,也就是说我们需要启动一个未注册的Activity,因此需要对Activity的启动过程有个了解。
启动Activity时会请求AMS创建Activity,这里的AMS指的是ActivityManagerService,AMS所属的进程与宿主(发起者)不属于同一个进程,AMS位于SystemServer进程中。
应用程序进程与AMS之间的通信是通过Binder来实现的,AMS要管理所有APP的启动请求,因此我们不能在SystemServer进程中进行相应的Hook,那么我们只能在应用进程中进行相应的Hook。
如果我们启动一个未注册的Activity,AMS会去检查AndroidManifest中是否注册了该Activity,如果未注册会报错。
为了让AMS验证通过,需要启动一个预先在AndroidManifest中注册的Activity,我们称之为占坑,在启动插件Activity时替换为占坑Activity,达到一个欺上瞒下的作用,当AMS验证通过之后,需要将启动的占坑Activity替换为插件Activity。
总结下来Activity的插件化需要做两件事:
- 将请求启动的插件Activity替换为占坑Activity。
- 绕过AMS验证后,将占坑Activity替换为插件Activity。
什么时候将插件Activity替换为占坑Activity?又是什么时候还原插件Activity?这需要我们对Activity的启动流程有个相应的认识。
我们在Activity中调用startActivity方法如下:
@Override
public void startActivity(Intent intent) {
this.startActivity(intent, null);
}
@Override
public void startActivity(Intent intent, @Nullable Bundle options) {
if (options != null) {
startActivityForResult(intent, -1, options);
} else {
startActivityForResult(intent, -1);
}
}
调用startActivityForResult方法:
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options) {
if (mParent == null) {
//Activity启动
options = transferSpringboardActivityOptions(options);
Instrumentation.ActivityResult ar =
mInstrumentation.execStartActivity(
this, mMainThread.getApplicationThread(), mToken, this,
intent, requestCode, options);
if (ar != null) {
mMainThread.sendActivityResult(
mToken, mEmbeddedID, requestCode, ar.getResultCode(),
ar.getResultData());
}
if (requestCode >= 0) {
mStartedActivity = true;
}
cancelInputsAndStartExitTransition(options);
windows.
} else {
if (options != null) {
mParent.startActivityFromChild(this, intent, requestCode, options);
} else {
mParent.startActivityFromChild(this, intent, requestCode);
}
}
}
startActivityForResult方法中通过调用mInstrumentation的execStartActivity方法来启动Activity,这个mInstrumentation是Activity的成员变量,在ActivityThread的performLaunchActivity方法中通过Activity的attach方法传入,同时Activity的创建也是在performLaunchActivity方法中创建的,通过mInstrumentation.newActivity。
//:/frameworks/base/core/java/android/app/ActivityThread.java
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
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);
}
}
...
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);
...
}
综上所述Instrumentation提供了execStartActivity方法来启动Activity,newActivity方法来创建Activity。因此,第一种方案就是用代理Instrumentation来替代Activity的Instrumentation,并在代理Instrumentation的execStartActivity方法中替换为占坑Activity,在newActivity方法还原插件Activity。
现在我们基于第一种方案Hook Instrumentation来实现Activity的插件化。
首先创建占坑Activity:
public class StubActivity extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_stub);
}
}
创建插件Activity:
public class TargetActivity extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_target);
}
}
并在AndroidManifest.xml中注册占坑Activity:
在AndroidManifest.xml中没有注册插件Activity,这时如果启动插件Activity会报错。
最后Hook Instrumentation,将ActivityThread中的成员变量Instrumentation替换成代理的Instrumentation。
创建代理Instrumentation类:
public class InstrumentationProxy extends Instrumentation {
private Instrumentation mInstrumentation;
private PackageManager mPackageManager;
public InstrumentationProxy(Instrumentation instrumentation, PackageManager packageManager) {
this.mInstrumentation = instrumentation;
this.mPackageManager = packageManager;
}
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options) {
List resolveInfo = mPackageManager.queryIntentActivities(intent, PackageManager.MATCH_ALL);
//判断启动的插件Activity是否在AndroidManifest.xml中注册过
if (null == resolveInfo || resolveInfo.size() == 0) {
//保存目标插件
intent.putExtra(HookHelper.REQUEST_TARGET_INTENT_NAME, intent.getComponent().getClassName());
//设置为占坑Activity
intent.setClassName(who, "com.glh.haiproject01.StubActivity");
}
try {
Method execStartActivity = Instrumentation.class.getDeclaredMethod("execStartActivity",
Context.class, IBinder.class, IBinder.class, Activity.class,
Intent.class, int.class, Bundle.class);
return (ActivityResult) execStartActivity.invoke(mInstrumentation, who, contextThread, token, target, intent, requestCode, options);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
return null;
}
public Activity newActivity(ClassLoader cl, String className, Intent intent) throws InstantiationException,
IllegalAccessException, ClassNotFoundException {
String intentName=intent.getStringExtra(HookHelper.REQUEST_TARGET_INTENT_NAME);
if(!TextUtils.isEmpty(intentName)){
return super.newActivity(cl,intentName,intent);
}
return super.newActivity(cl,className,intent);
}
}
代理类InstrumentationProxy的execStartActivity方法先判断插件Activity是否在AndroidManifest.xml中注册过,如果没有注册过就需要替换占坑的Activity,在newActivity方法中还原插件Activity。
代理类InstrumentationProxy写完后,需要对ActivityThread的成员变量mInstrumentation进行替换。
public class MyApplication extends Application {
@Override
protected void attachBaseContext(Context base) {
super.attachBaseContext(base);
hookActivityThreadInstrumentation();
}
private void hookActivityThreadInstrumentation(){
try {
Class> activityThreadClass=Class.forName("android.app.ActivityThread");
Field activityThreadField=activityThreadClass.getDeclaredField("sCurrentActivityThread");
activityThreadField.setAccessible(true);
//获取ActivityThread对象sCurrentActivityThread
Object activityThread=activityThreadField.get(null);
Field instrumentationField=activityThreadClass.getDeclaredField("mInstrumentation");
instrumentationField.setAccessible(true);
//从sCurrentActivityThread中获取成员变量mInstrumentation
Instrumentation instrumentation= (Instrumentation) instrumentationField.get(activityThread);
//创建代理对象InstrumentationProxy
InstrumentationProxy proxy=new InstrumentationProxy(instrumentation,getPackageManager());
//将sCurrentActivityThread中成员变量mInstrumentation替换成代理类InstrumentationProxy
instrumentationField.set(activityThread,proxy);
} catch (NoSuchFieldException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
这时我们在主界面点击跳转插件Activity:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.btn_startActivity).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this,TargetActivity.class);
startActivity(intent);
}
});
}
}
运行效果: