Android Measure流程(三)

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导航：Android Measure流程(一)juejin.cn/post/716850… Android Measure流程(二)juejin.cn/post/716924…

ViewRootImpl

同样，直接debug

可以看出ViewRootImpl是在WindowManagerGlobal里面初始化的。

具体如下：

public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    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");
    }

    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
    if (parentWindow != null) {
        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.
        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);
                }
            }
        }
        // 初始化ViewRootImpl
        root = new ViewRootImpl(view.getContext(), display);

        view.setLayoutParams(wparams);

        mViews.add(view);
        mRoots.add(root);
        mParams.add(wparams);

        // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            if (index >= 0) {
                removeViewLocked(index, true);
            }
            throw e;
        }
    }
}

那view哪里哪来的呢，我们看调用栈是从WindowManagerImpl的addview传过来的

WindowManagerImpl的addview实现如下：

@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}

这里view也是传递过来的，看来还需要继续往上追。再看调用栈，是ActivityThread里面的handleResumeActivity

我们知道app的创建过程就需要调用ActivityThread的main()进行初始化，也正是在main（）里面我们开启了looper.loop

具体实现如下：

@Override
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
        String reason) {

    unscheduleGcIdler();
    mSomeActivitiesChanged = true;

    final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
    if (r == null) {
        // We didn't actually resume the activity, so skipping any follow-up actions.
        return;
    }

    final Activity a = r.activity;
    ....
    if (r.window == null && !a.mFinished && willBeVisible) {
        r.window = r.activity.getWindow();
        //这里是传递的view也就是decorview
        View decor = r.window.getDecorView();
        decor.setVisibility(View.INVISIBLE);
        ViewManager wm = a.getWindowManager();
        WindowManager.LayoutParams l = r.window.getAttributes();
        a.mDecor = decor;
        .....
        if (a.mVisibleFromClient) {
            if (!a.mWindowAdded) {
                a.mWindowAdded = true;
                //这里调用了windowManagerImpl的addview
                wm.addView(decor, l);
            } else {
                a.onWindowAttributesChanged(l);
            }
        }
    .......
    Looper.myQueue().addIdleHandler(new Idler());
}

我们这里知道view是在哪里传递过来的了

我们继续追下去，会发现他是在ActiviryThread的Hnadler调用的，这里我们要做的事情就是知道是谁通过looper发送的这一个消息。

我们根据调用栈追到最后会到ActivityThread里面，也就是Lopper.loop()处。