Activity启动流程阅读

来源：互联网发布：linux如何卸载jdk 编辑：程序博客网时间：2024/05/16 07:00

启动Activity
一般我们使用context.startActivity();

  public abstract void startActivity(Intent intent);

Context是个抽象类，接着找Context的实现类ContextImpl.java

 public void startActivity(Intent intent) {        warnIfCallingFromSystemProcess();        startActivity(intent, null);    }

调用

  @Override    public void startActivity(Intent intent, Bundle options) {        warnIfCallingFromSystemProcess();        if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {            throw new AndroidRuntimeException(                    "Calling startActivity() from outside of an Activity "                    + " context requires the FLAG_ACTIVITY_NEW_TASK flag."                    + " Is this really what you want?");        }        mMainThread.getInstrumentation().execStartActivity(                getOuterContext(), mMainThread.getApplicationThread(), null,                (Activity) null, intent, -1, options);    }

执行 execStartActivity

public ActivityResult execStartActivity(        Context who, IBinder contextThread, IBinder token, String target,        Intent intent, int requestCode, Bundle options) {        IApplicationThread whoThread = (IApplicationThread) contextThread;        if (mActivityMonitors != null) {            synchronized (mSync) {                final int N = mActivityMonitors.size();                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();            int result = ActivityManagerNative.getDefault()                .startActivity(whoThread, who.getBasePackageName(), intent,                        intent.resolveTypeIfNeeded(who.getContentResolver()),                        token, target, requestCode, 0, null, options);            checkStartActivityResult(result, intent);        } catch (RemoteException e) {            throw new RuntimeException("Failure from system", e);        }        return null;    }

循环mActivityMonitors 集合如果监视器里有相应的Activity直接返回
否则执行 ActivityManagerNative.getDefault()
.startActivity()

ActivityManagerNative.getDefault() 得到的 IActivityManager 接口需要去找实现类 ActivityManagerNative
最终startActivity() 是通过 ActivityManagerProxy 代理实现的

 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;    }

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