那就来到了WindowManager中的addView方法

查看WindowManager中没有addView方法，但是ViewManager中有，那我们再看下谁实现了WindowManager呢

可找到是WindowManagerImpl中实现此addView方法,因为WindowManagerImpl继承了WindowManager：

/*
 * @see WindowManager
 * @see WindowManagerGlobal
 * @hide
 */
public final class WindowManagerImpl implements WindowManager {
...
    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyTokens(params);
        mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,
                mContext.getUserId());
    }

此方法又调用了 WindowManagerGlobal中的addView方法，并将view，窗口属性，要显示的屏幕，父window，以及user id传入

WindowManagerGlobal.java - OpenGrok cross reference for /frameworks/base/core/java/android/view/WindowManagerGlobal.java

    public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow, int userId) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (display == null) {
            throw new IllegalArgumentException("display must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }
//获取窗口布局属性
        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
        if (parentWindow != null) {
//如果父窗口不为空，则调整当前父窗口下所有子窗口布局的属性
            parentWindow.adjustLayoutParamsForSubWindow(wparams);
        } else {
            // If there's no parent, then hardware acceleration for this view is
            // set from the application's hardware acceleration setting.
            final Context context = view.getContext();
            if (context != null
                    && (context.getApplicationInfo().flags
                            & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
                wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
            }
        }

        ViewRootImpl root;
        View panelParentView = null;

        synchronized (mLock) {
            // Start watching for system property changes.
            if (mSystemPropertyUpdater == null) {
                mSystemPropertyUpdater = new Runnable() {
                    @Override public void run() {
                        synchronized (mLock) {
                            for (int i = mRoots.size() - 1; i >= 0; --i) {
                                mRoots.get(i).loadSystemProperties();
                            }
                        }
                    }
                };
                SystemProperties.addChangeCallback(mSystemPropertyUpdater);
            }

            int index = findViewLocked(view, false);
            if (index >= 0) {
                if (mDyingViews.contains(view)) {
                    // Don't wait for MSG_DIE to make it's way through root's queue.
                    mRoots.get(index).doDie();
                } else {
                    throw new IllegalStateException("View " + view
                            + " has already been added to the window manager.");
                }
                // The previous removeView() had not completed executing. Now it has.
            }

            // If this is a panel window, then find the window it is being
            // attached to for future reference.
//如果是子窗口
            if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                    wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
                final int count = mViews.size();
                for (int i = 0; i < count; i++) {
                    if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                        panelParentView = mViews.get(i);
                    }
                }
            }

            IWindowSession windowlessSession = null;
            // If there is a parent set, but we can't find it, it may be coming
            // from a SurfaceControlViewHost hierarchy.
//如果token不为空并且不是子窗口
            if (wparams.token != null && panelParentView == null) {
                for (int i = 0; i < mWindowlessRoots.size(); i++) {
                    ViewRootImpl maybeParent = mWindowlessRoots.get(i);
                    if (maybeParent.getWindowToken() == wparams.token) {
//获取WindowSession
                        windowlessSession = maybeParent.getWindowSession();
                        break;
                    }
                }
            }

            if (windowlessSession == null) {
//如果windowlessSession为空
                root = new ViewRootImpl(view.getContext(), display);
            } else {
//如果windowlessSession不为空，则在此处传入windowlessSession
                root = new ViewRootImpl(view.getContext(), display,
                        windowlessSession, new WindowlessWindowLayout());
            }
//将窗口布局属性设置进view
            view.setLayoutParams(wparams);
//将此view添加进mViews
            mViews.add(view);
//将此root添加进MRoots
            mRoots.add(root);
//将此窗口布局属性添加进mParams
            mParams.add(wparams);

            // do this last because it fires off messages to start doing things
            try {
//将view，窗口属性和子窗口，user id 设置进ViewRootImpl
                root.setView(view, wparams, panelParentView, userId);
            } catch (RuntimeException e) {
                final int viewIndex = (index >= 0) ? index : (mViews.size() - 1);
                // BadTokenException or InvalidDisplayException, clean up.
                if (viewIndex >= 0) {
                    removeViewLocked(viewIndex, true);
                }
                throw e;
            }
        }
    }

3. ViewRootImpl#setView

然后就从WindowManagerGlobal走到了ViewRootImpl中

http://aospxref.com/android-14.0.0_r2/xref/frameworks/base/core/java/android/view/ViewRootImpl.java#1214

    final IWindowSession mWindowSession;

    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        setView(view, attrs, panelParentView, UserHandle.myUserId());
    }

    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView, int userId) {
        synchronized (this) {
//这个mView和上一个方法中的可不一样，当窗口detach后，这个mView会被置为空
            if (mView == null) {
                mView = view;
...

                mWindowAttributes.copyFrom(attrs)
...
                // Schedule the first layout -before- adding to the window
                // manager, to make sure we do the relayout before receiving
                // any other events from the system.
//首先需要layout
                requestLayout();
...
//这个是很重要的一步
                    res = mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(), userId,
                            mInsetsController.getRequestedVisibleTypes(), inputChannel, mTempInsets, mTempControls, attachedFrame, compatScale);
...
                mPendingAlwaysConsumeSystemBars = mAttachInfo.mAlwaysConsumeSystemBars;
                mInsetsController.onStateChanged(mTempInsets);
                mInsetsController.onControlsChanged(mTempControls.get());
                final InsetsState state = mInsetsController.getState();
                final Rect displayCutoutSafe = mTempRect;
                state.getDisplayCutoutSafe(displayCutoutSafe);
                final WindowConfiguration winConfig = getCompatWindowConfiguration();
                mWindowLayout.computeFrames(mWindowAttributes, state,
                        displayCutoutSafe, winConfig.getBounds(), winConfig.getWindowingMode(),
                        UNSPECIFIED_LENGTH, UNSPECIFIED_LENGTH,
                        mInsetsController.getRequestedVisibleTypes(), 1f /* compactScale */, mTmpFrames);
                setFrame(mTmpFrames.frame, true /* withinRelayout */);
...
    }

接着往下走，就会讲到WindowSession.addToDisplayAsUser方法

4. WindowSession.addToDisplayAsUser

这里是涉及到AIDL通信，因为mWindowSession是final IWindowSession mWindowSession;

用到的AIDL文件如下：

frameworks/base/core/java/android/view/IWindowSession.aidl

http://aospxref.com/android-14.0.0_r2/xref/frameworks/base/core/java/android/view/IWindowSession.aidl

 在Client端，WindowlessWindowManager实现了IWindowSession

    /**
     * IWindowSession implementation. Currently this class doesn't need to support for multi-user.
     */
    @Override
    public int addToDisplayAsUser(IWindow window, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, int userId, @InsetsType int requestedVisibleTypes,
            InputChannel outInputChannel, InsetsState outInsetsState,
            InsetsSourceControl.Array outActiveControls, Rect outAttachedFrame,
            float[] outSizeCompatScale) {
        return addToDisplay(window, attrs, viewVisibility, displayId, requestedVisibleTypes,
                outInputChannel, outInsetsState, outActiveControls, outAttachedFrame,
                outSizeCompatScale);
    }

    @Override
    public int addToDisplay(IWindow window, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, @InsetsType int requestedVisibleTypes,
            InputChannel outInputChannel, InsetsState outInsetsState,
            InsetsSourceControl.Array outActiveControls, Rect outAttachedFrame,
            float[] outSizeCompatScale) {
// setParent方法作用如下
// Set a parent surface for our new SurfaceControl.
// 给我们的new SurfaceControl设置父surface
// Child surfaces are constrained to the onscreen region of their parent.
//子surfaces被限制在它们的父surface之上
// Furthermore they stack relatively in Z order, and inherit the transformation of the parent.
//此外这些stack按照Z值排序，并继承父级的transformation 

//window leash 图层创建
        final SurfaceControl leash = new SurfaceControl.Builder(mSurfaceSession)
                .setName(attrs.getTitle().toString() + "Leash")
                .setCallsite("WindowlessWindowManager.addToDisplay")
                .setParent(getParentSurface(window, attrs))
                .build();
//window图层创建
        final SurfaceControl sc = new SurfaceControl.Builder(mSurfaceSession)
                .setFormat(attrs.format)
                .setBLASTLayer()
                .setName(attrs.getTitle().toString())
                .setCallsite("WindowlessWindowManager.addToDisplay")
                .setHidden(false)
                .setParent(leash)
                .build();
//在当前文件的最上面有State的定义，主要就是将入参赋值给State的全局变量
        final State state = new State(sc, attrs, displayId, window, leash, /* frame= */ new Rect());
        synchronized (this) {
            State parentState = mStateForWindow.get(attrs.token);
            if (parentState != null) {
                state.mAttachedFrame = parentState.mFrame;
            }

            // Give the first window the mFocusGrantToken since that's the token the host can use
            // to give focus to the embedded.
            if (mStateForWindow.isEmpty()) {
                state.mFocusGrantToken = mFocusGrantToken;
            } else {
                state.mFocusGrantToken = new Binder();
            }

            mStateForWindow.put(window.asBinder(), state);
        }

        if (state.mAttachedFrame == null) {
            outAttachedFrame.set(0, 0, -1, -1);
        } else {
            outAttachedFrame.set(state.mAttachedFrame);
        }
        outSizeCompatScale[0] = 1f;

        if (((attrs.inputFeatures &
                WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0)) {
            try {
                if (mRealWm instanceof IWindowSession.Stub) {
                    mRealWm.grantInputChannel(displayId,
                            new SurfaceControl(sc, "WindowlessWindowManager.addToDisplay"),
                            window, mHostInputToken, attrs.flags, attrs.privateFlags,
                            attrs.inputFeatures, attrs.type,
                            attrs.token, state.mFocusGrantToken, attrs.getTitle().toString(), outInputChannel);
                } else {
                    mRealWm.grantInputChannel(displayId, sc, window, mHostInputToken, attrs.flags, attrs.privateFlags, attrs.inputFeatures, attrs.type, attrs.token,
                  state.mFocusGrantToken, attrs.getTitle().toString(), outInputChannel);
                }
                state.mInputChannelToken =
                        outInputChannel != null ? outInputChannel.getToken() : null;
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to grant input to surface: ", e);
            }
        }

        final int res = WindowManagerGlobal.ADD_OKAY | WindowManagerGlobal.ADD_FLAG_APP_VISIBLE |
                        WindowManagerGlobal.ADD_FLAG_USE_BLAST;

        // Include whether the window is in touch mode.
        return isInTouchModeInternal(displayId) ? res | WindowManagerGlobal.ADD_FLAG_IN_TOUCH_MODE
                : res;
    }

这里我们来看一下mRealWm的赋值过程

然后就走到了WindowManagerGlobal这里去获取WindowSession

WindowManagerGlobal.java - OpenGrok cross reference for /frameworks/base/core/java/android/view/WindowManagerGlobal.java

    @UnsupportedAppUsage
    public static IWindowSession getWindowSession() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowSession == null) {
                try {
// Emulate the legacy behavior.  The global instance of InputMethodManager
// was instantiated here.
// TODO(b/116157766): Remove this hack after cleaning up @UnsupportedAppUsage
                    InputMethodManager.ensureDefaultInstanceForDefaultDisplayIfNecessary();
//第一步
                    IWindowManager windowManager = getWindowManagerService();
//第二步
                    sWindowSession = windowManager.openSession(
                            new IWindowSessionCallback.Stub() {
                                @Override
                                public void onAnimatorScaleChanged(float scale) {
                                    ValueAnimator.setDurationScale(scale);
                                }
                            });
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            return sWindowSession;
        }
    }

 在第一步中，通过getWindowManagerService方法获取了server端binder对象，即获取了WMS服务, 看代码是单例模式，可以看出来这个sWindowSession是一个单例，也就是一个应用的所有ViewRootImpl的WindowSession都是同一个，也就是一个应用只有一个WindowSession,用于与WMS进行通信。

    @UnsupportedAppUsage
    public static IWindowManager getWindowManagerService() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowManagerService == null) {
//获取server端binder对象，即获取WMS服务
                sWindowManagerService = IWindowManager.Stub.asInterface(
                        ServiceManager.getService("window"));
...
            return sWindowManagerService;
        }
    }

在第二步中，则调用到了Server端服务WMS中的方法，这里也是单例模式的写法，sWindowManagerService 在Client端也只有一个对象。

WindowManagerService.java - OpenGrok cross reference for /frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java

然后在WMS中new了一个Session，Session实例化相关如下 

Session.java - OpenGrok cross reference for /frameworks/base/services/core/java/com/android/server/wm/Session.java

来看看WMS，其实也是继承了 IWindowSession.Stub

/** {@hide} */
public class WindowManagerService extends IWindowManager.Stub implements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {

从上我们总结出：

一个应用只有一个WindowSession, 用于与WMS进行通信。

5. Session#grantInputChannel

接着讲上文中的 grantInputChannel方法

Session.java - OpenGrok cross reference for /frameworks/base/services/core/java/com/android/server/wm/Session.java

    @Override
    public void grantInputChannel(int displayId, SurfaceControl surface,
            IWindow window, IBinder hostInputToken, int flags, int privateFlags, int type, int inputFeatures, IBinder windowToken, IBinder focusGrantToken, String inputHandleName,
            InputChannel outInputChannel) {
...
//这里会调用Server端的grantInputChannel方法
            mService.grantInputChannel(this, mUid, mPid, displayId, surface, window, hostInputToken, flags, mCanAddInternalSystemWindow ? privateFlags : 0,
                    type, inputFeatures, windowToken, focusGrantToken, inputHandleName,
                    outInputChannel);
...
    }

下面是一个关于以上流程的setting主页面启动流程

05-25 12:58:21.791  1909  2175 I wm_task_created: 441
05-25 12:58:21.795  1909  2175 I wm_task_moved: [441,441,0,1,2]
05-25 12:58:21.795  1909  2175 I wm_task_to_front: [0,441,0]
05-25 12:58:21.795  1909  2175 I wm_create_task: [0,441,441,0]
05-25 12:58:21.795  1909  2175 I wm_create_activity: [0,232997572,441,com.android.settings/.homepage.SettingsHomepageActivity,android.settings.SETTINGS,NULL,NULL,335544320]
05-25 12:58:21.795  1909  2175 I wm_task_moved: [441,441,0,1,2]
05-25 12:58:22.265  1909  3494 I wm_restart_activity: [0,232997572,441,com.android.settings/.homepage.SettingsHomepageActivity]
05-25 12:58:22.267  1909  3494 I wm_set_resumed_activity: [0,com.android.settings/.homepage.SettingsHomepageActivity,minimalResumeActivityLocked - onActivityStateChanged]
05-25 12:58:22.363  2518  2518 I wm_on_create_called: [232997572,com.android.settings.homepage.SettingsHomepageActivity,performCreate,66]
05-25 12:58:22.457  2518  2518 I wm_on_start_called: [232997572,com.android.settings.homepage.SettingsHomepageActivity,handleStartActivity,92]
05-25 12:58:22.460  2518  2518 V ActivityThread: Performing resume of ActivityRecord{a4a98fc token=android.os.BinderProxy@c7155ef {com.android.settings/com.android.settings.homepage.SettingsHomepageActivity}} finished=false
05-25 12:58:22.460  2518  2518 I wm_on_resume_called: [232997572,com.android.settings.homepage.SettingsHomepageActivity,RESUME_ACTIVITY,0]
05-25 12:58:22.525  2518  2518 V ActivityThread: Resume ActivityRecord{a4a98fc token=android.os.BinderProxy@c7155ef {com.android.settings/com.android.settings.homepage.SettingsHomepageActivity}} started activity: false, hideForNow: false, finished: false
05-25 12:58:22.545  1909  2175 V WindowManager: Attaching Window{a90e6ab u0 com.android.settings/com.android.settings.homepage.SettingsHomepageActivity} token=ActivityRecord{de342c4 u0 com.android.settings/.homepage.SettingsHomepageActivity t441}
05-25 12:58:22.552  2518  2518 V ActivityThread: Resuming ActivityRecord{a4a98fc token=android.os.BinderProxy@c7155ef {com.android.settings/com.android.settings.homepage.SettingsHomepageActivity}} with isForward=true
05-25 12:58:22.552  2518  2518 V ActivityThread: Scheduling idle handler for ActivityRecord{a4a98fc token=android.os.BinderProxy@c7155ef {com.android.settings/com.android.settings.homepage.SettingsHomepageActivity}}
05-25 12:58:22.553  2518  2518 I wm_on_top_resumed_gained_called: [232997572,com.android.settings.homepage.SettingsHomepageActivity,topStateChangedWhenResumed]
05-25 12:58:22.769  1909  1971 I wm_activity_launch_time: [0,232997572,com.android.settings/.homepage.SettingsHomepageActivity,970]

6. WindowManagerService#grantInputChannel

这里就到了Server端，以上都是Client端。

由于本篇文章已经过长，故Server端的另起一篇文章分析。