android Activity启动过程(一)从startActivty开始说起
从启动startActivity开始说起
MainActivity.startActivity()
Activity.startActivity()
Activity.startActivityForResult
Instrumentation.execStartActivty
ActivityManagerNative.getDefault().startActivity()
调用startActivty实际上最后还是调用了startActivityForResult 方法
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 { // Note we want to go through this call for compatibility with // applications that may have overridden the method. startActivityForResult(intent, -1); } } @Override public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) { if (mParent == null) { //真正执行启动activity的代码逻辑 Instrumentation.ActivityResult ar = mInstrumentation.execStartActivity( this, mMainThread.getApplicationThread(), mToken, this, intent, requestCode, options); //启动activity返回的结果处理 if (ar != null) { mMainThread.sendActivityResult( mToken, mEmbeddedID, requestCode, ar.getResultCode(), ar.getResultData()); } if (requestCode >= 0) { mStartedActivity = true; } cancelInputsAndStartExitTransition(options); // TODO Consider clearing/flushing other event sources and events for child windows. } else { if (options != null) { mParent.startActivityFromChild(this, intent, requestCode, options); } else { // Note we want to go through this method for compatibility with // existing applications that may have overridden it. mParent.startActivityFromChild(this, intent, requestCode); } } }
实际上调用的启动startActivityForResult方法的最终还是通过Instrumentation类来执行execStartActivity
public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) { //这个whoThread执行了启动activity IApplicationThread whoThread = (IApplicationThread) contextThread; Uri referrer = target != null ? target.onProvideReferrer() : null; if (referrer != null) { intent.putExtra(Intent.EXTRA_REFERRER, referrer); } if (mActivityMonitors != null) { synchronized (mSync) { final int N = mActivityMonitors.size(); //遍历一遍，查询是否存在这个activity，activity类存放在intent中。 for (int i = 0; i < N; i++) { final ActivityMonitor am = mActivityMonitors.get(i); if (am.match(who, null, intent)) { am.mHits++; if (am.isBlocking()) { return requestCode >= 0 ? am.getResult() : null; } break; } } } } try { intent.migrateExtraStreamToClipData(); intent.prepareToLeaveProcess(); //这里通过ActivityManager启动了activity int result = ActivityManagerNative.getDefault() .startActivity(whoThread, who.getBasePackageName(), intent, intent.resolveTypeIfNeeded(who.getContentResolver()), token, target != null ? target.mEmbeddedID : null, requestCode, 0, null, options); //检查启动activity返回的结果 checkStartActivityResult(result, intent); } catch (RemoteException e) { throw new RuntimeException("Failure from system", e); } return null; }
执行activity的启动过程的是ActivityManagerNative.getDefault().startActivity
public abstract class ActivityManagerNative extends Binder implements IActivityManager { private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() { protected IActivityManager create() { IBinder b = ServiceManager.getService("activity"); if (false) { Log.v("ActivityManager", "default service binder = " + b); } IActivityManager am = asInterface(b); if (false) { Log.v("ActivityManager", "default service = " + am); } return am; } }; static public IActivityManager asInterface(IBinder obj) { if (obj == null) { return null; } IActivityManager in = (IActivityManager)obj.queryLocalInterface(descriptor); if (in != null) { return in; } return new ActivityManagerProxy(obj); } static public IActivityManager getDefault() { return gDefault.get(); } public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException { switch (code) { case START_ACTIVITY_TRANSACTION: { data.enforceInterface(IActivityManager.descriptor); IBinder b = data.readStrongBinder(); IApplicationThread app = ApplicationThreadNative.asInterface(b); String callingPackage = data.readString(); Intent intent = Intent.CREATOR.createFromParcel(data); String resolvedType = data.readString(); IBinder resultTo = data.readStrongBinder(); String resultWho = data.readString(); int requestCode = data.readInt(); int startFlags = data.readInt(); ProfilerInfo profilerInfo = data.readInt() != 0 ? ProfilerInfo.CREATOR.createFromParcel(data) : null; Bundle options = data.readInt() != 0 ? Bundle.CREATOR.createFromParcel(data) : null; int result = startActivity(app, callingPackage, intent, resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, options); reply.writeNoException(); reply.writeInt(result); return true; } ... } }
- gDefault.get()返回的就是一个IActivityManager的单例gDefault
- IBinder b = ServiceManager.getService("activity")获取一个IBinder这个就是和远程通信的, 也就是ActivityManagerService
- 可以在asInterface(IBinder obj) 调用就是返回的ActivityManagerProxy就是ActivityManagerService的远程代理类。
ActivityManagerNative.java#ActivityManagerProxy
class ActivityManagerProxy implements IActivityManager { private IBinder mRemote; public ActivityManagerProxy(IBinder remote) { mRemote = remote; } public IBinder asBinder() { return mRemote; } public int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException { Parcel data = Parcel.obtain(); Parcel reply = Parcel.obtain(); data.writeInterfaceToken(IActivityManager.descriptor); data.writeStrongBinder(caller != null ? caller.asBinder() : null); data.writeString(callingPackage); intent.writeToParcel(data, 0); data.writeString(resolvedType); data.writeStrongBinder(resultTo); data.writeString(resultWho); data.writeInt(requestCode); data.writeInt(startFlags); if (profilerInfo != null) { data.writeInt(1); profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE); } else { data.writeInt(0); } if (options != null) { data.writeInt(1); options.writeToParcel(data, 0); } else { data.writeInt(0); } mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0); reply.readException(); int result = reply.readInt(); reply.recycle(); data.recycle(); return result; } ... }
mRemote是一个IBinder，调用了IBinder的transact()方法,这说明了启动Activity实际上也是进行了进程间的通信
