源碼：8.1系統(tǒng)

1.Surface implements Parcelable

說明Surface可以直接跨進(jìn)程傳遞，無須再封裝

2.竟然是跨進(jìn)程傳遞，自然涉及的關(guān)鍵方法為writeToParcel、readFromParcel

3.重點(diǎn)分析

1）writeToParcel

Surface.java
    public void writeToParcel(Parcel dest, int flags) {
        if (dest == null) {
            throw new IllegalArgumentException("dest must not be null");
        }
        synchronized (mLock) {
            // NOTE: This must be kept synchronized with the native parceling code
            // in frameworks/native/libs/Surface.cpp
            dest.writeString(mName);
            dest.writeInt(mIsSingleBuffered ? 1 : 0);
            nativeWriteToParcel(mNativeObject, dest);//1
        }
        if ((flags & Parcelable.PARCELABLE_WRITE_RETURN_VALUE) != 0) {
            release();
        }
    }
    
    重點(diǎn)分析注解1：
    android_view_Surface.cpp
    static void nativeWriteToParcel(JNIEnv* env, jclass clazz,
        jlong nativeObject, jobject parcelObj) {
    Parcel* parcel = parcelForJavaObject(env, parcelObj);
    if (parcel == NULL) {
        doThrowNPE(env);
        return;
    }
    sp<Surface> self(reinterpret_cast<Surface *>(nativeObject));
    android::view::Surface surfaceShim;
    if (self != nullptr) {
        surfaceShim.graphicBufferProducer = self->getIGraphicBufferProducer();//重點(diǎn)2
    }
    // Calling code in Surface.java has already written the name of the Surface
    // to the Parcel
    surfaceShim.writeToParcel(parcel, /*nameAlreadyWritten*/true);
    }
    
    分析重點(diǎn)2：
    Surface.cpp
    sp<IGraphicBufferProducer> Surface::getIGraphicBufferProducer() const {
    return mGraphicBufferProducer;
    }
    
    小結(jié)：
    Surface.writeToParcel的關(guān)鍵對(duì)象為mGraphicBufferProducer

2）readFromParcel

Surface.java
    public void readFromParcel(Parcel source) {
        if (source == null) {
            throw new IllegalArgumentException("source must not be null");
        }

        synchronized (mLock) {
            // nativeReadFromParcel() will either return mNativeObject, or
            // create a new native Surface and return it after reducing
            // the reference count on mNativeObject.  Either way, it is
            // not necessary to call nativeRelease() here.
            // NOTE: This must be kept synchronized with the native parceling code
            // in frameworks/native/libs/Surface.cpp
            mName = source.readString();
            mIsSingleBuffered = source.readInt() != 0;
            setNativeObjectLocked(nativeReadFromParcel(mNativeObject, source));
        }
    }
    
    重點(diǎn)看nativeReadFromParcel
    static jlong nativeReadFromParcel(JNIEnv* env, jclass clazz,
        jlong nativeObject, jobject parcelObj) {
    Parcel* parcel = parcelForJavaObject(env, parcelObj);
    if (parcel == NULL) {
        doThrowNPE(env);
        return 0;
    }

    android::view::Surface surfaceShim;

    // Calling code in Surface.java has already read the name of the Surface
    // from the Parcel
    surfaceShim.readFromParcel(parcel, /*nameAlreadyRead*/true);

    sp<Surface> self(reinterpret_cast<Surface *>(nativeObject));

    // update the Surface only if the underlying IGraphicBufferProducer
    // has changed.
    if (self != nullptr
            && (IInterface::asBinder(self->getIGraphicBufferProducer()) ==
                    IInterface::asBinder(surfaceShim.graphicBufferProducer))) {
        // same IGraphicBufferProducer, return ourselves
        return jlong(self.get());
    }

    sp<Surface> sur;
    if (surfaceShim.graphicBufferProducer != nullptr) {
        // we have a new IGraphicBufferProducer, create a new Surface for it
        sur = new Surface(surfaceShim.graphicBufferProducer, true);
        // and keep a reference before passing to java
        sur->incStrong(&sRefBaseOwner);
    }

    if (self != NULL) {
        // and loose the java reference to ourselves
        self->decStrong(&sRefBaseOwner);
    }

    return jlong(sur.get());
    }
    關(guān)鍵點(diǎn)為surfaceShim.graphicBufferProducer，這是讀取出來的
    
    小結(jié)：
    Surface.readFromParcel的關(guān)鍵對(duì)象為mGraphicBufferProducer

3）總結(jié)

Surface跨進(jìn)程傳遞的是mGraphicBufferProducer，不是Buffer

4.Activity中的Surface是怎么跨進(jìn)程傳回應(yīng)用本身？

1)我們知道Activity真正涉及Surface傳遞的地方，在ViewRootImpl.java，代碼跟蹤：

ViewRootImpl.java
private void performTraversals() {
    ······
    relayoutResult = relayoutWindow(params, viewVisibility, insetsPending);
    ······
}

 private int relayoutWindow(WindowManager.LayoutParams params, int viewVisibility,
            boolean insetsPending) throws RemoteException {
     ······
     int relayoutResult = mWindowSession.relayout(
                mWindow, mSeq, params,
                (int) (mView.getMeasuredWidth() * appScale + 0.5f),
                (int) (mView.getMeasuredHeight() * appScale + 0.5f),
                viewVisibility, insetsPending ? WindowManagerGlobal.RELAYOUT_INSETS_PENDING : 0,
                mWinFrame, mPendingOverscanInsets, mPendingContentInsets, mPendingVisibleInsets,
                mPendingStableInsets, mPendingOutsets, mPendingBackDropFrame,
                mPendingMergedConfiguration, mSurface);
     ······             
}
注意：
final Surface mSurface = new Surface();
mSurface沒有什么實(shí)際的內(nèi)容，說明對(duì)它進(jìn)行操作的地方，在別處。

Session.java
    public int relayout(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int requestedWidth, int requestedHeight, int viewFlags,
            int flags, Rect outFrame, Rect outOverscanInsets, Rect outContentInsets,
            Rect outVisibleInsets, Rect outStableInsets, Rect outsets, Rect outBackdropFrame,
            MergedConfiguration mergedConfiguration, Surface outSurface) {
        ······
        int res = mService.relayoutWindow(this, window, seq, attrs,
                requestedWidth, requestedHeight, viewFlags, flags,
                outFrame, outOverscanInsets, outContentInsets, outVisibleInsets,
                outStableInsets, outsets, outBackdropFrame, mergedConfiguration, outSurface);
        ······
        return res;
    }
    
WindowManagerService.java
    public int relayoutWindow(Session session, IWindow client, int seq,
            WindowManager.LayoutParams attrs, int requestedWidth,
            int requestedHeight, int viewVisibility, int flags,
            Rect outFrame, Rect outOverscanInsets, Rect outContentInsets,
            Rect outVisibleInsets, Rect outStableInsets, Rect outOutsets, Rect outBackdropFrame,
            MergedConfiguration mergedConfiguration, Surface outSurface) {
        ······
        result = createSurfaceControl(outSurface, result, win, winAnimator);
        ······
     }
     ViewRootImpl中的Surface傳遞到了WindowManagerService中
     
    private int createSurfaceControl(Surface outSurface, int result, WindowState win,
            WindowStateAnimator winAnimator) {
        ······
        WindowSurfaceController surfaceController;
        try {
            Trace.traceBegin(TRACE_TAG_WINDOW_MANAGER, "createSurfaceControl");
            surfaceController = winAnimator.createSurfaceLocked(win.mAttrs.type, win.mOwnerUid);
        } finally {
            Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
        }
        if (surfaceController != null) {
            surfaceController.getSurface(outSurface);//1
            if (SHOW_TRANSACTIONS) Slog.i(TAG_WM, "  OUT SURFACE " + outSurface + ": copied");
        } else {
            ······
        }
        ······
    }     
     
WindowSurfaceController.java
    void getSurface(Surface outSurface) {
        outSurface.copyFrom(mSurfaceControl);//2
    }
    1.mSurfaceControl為對(duì)象SurfaceControlWithBackground(SurfaceControlWithBackground extends SurfaceControl)
    2.WindowSurfaceController.getSurface目的，將Surface通過SurfaceControl綁定在一起
    3.java層的SurfaceControl會(huì)對(duì)應(yīng)native層的SurfaceControl，而native層的SurfaceControl會(huì)對(duì)應(yīng)一個(gè)native層的Surface
    
    
Surface.java
    public void copyFrom(SurfaceControl other) {
        if (other == null) {
            throw new IllegalArgumentException("other must not be null");
        }

        long surfaceControlPtr = other.mNativeObject;
        if (surfaceControlPtr == 0) {
            throw new NullPointerException(
                    "null SurfaceControl native object. Are you using a released SurfaceControl?");
        }
        long newNativeObject = nativeGetFromSurfaceControl(surfaceControlPtr);//3

        synchronized (mLock) {
            if (mNativeObject != 0) {
                nativeRelease(mNativeObject);
            }
            setNativeObjectLocked(newNativeObject);
        }
     }
     
android_view_Surface.cpp
      static jlong nativeGetFromSurfaceControl(JNIEnv* env, jclass clazz,
        jlong surfaceControlNativeObj) {
    /*
     * This is used by the WindowManagerService just after constructing
     * a Surface and is necessary for returning the Surface reference to
     * the caller. At this point, we should only have a SurfaceControl.
     */

    sp<SurfaceControl> ctrl(reinterpret_cast<SurfaceControl *>(surfaceControlNativeObj));
    sp<Surface> surface(ctrl->getSurface());//4
    if (surface != NULL) {
        surface->incStrong(&sRefBaseOwner);
    }
    return reinterpret_cast<jlong>(surface.get());
    }

SurfaceControl.cpp
sp<Surface> SurfaceControl::getSurface() const
{
    Mutex::Autolock _l(mLock);
    if (mSurfaceData == 0) {
        return generateSurfaceLocked();//5
    }
    return mSurfaceData;
}

sp<Surface> SurfaceControl::generateSurfaceLocked() const
{
    // This surface is always consumed by SurfaceFlinger, so the
    // producerControlledByApp value doesn't matter; using false.
    mSurfaceData = new Surface(mGraphicBufferProducer, false);

    return mSurfaceData;
}

2)小結(jié)

Activity本身創(chuàng)建的Surface為空對(duì)象，通過系統(tǒng)的SurfaceControl賦予了生機(jī)。
提示：
是否還記得SurfaceControl是用來截圖的接口文件？