要看View的绘制流程首先要看DectorView被添加到Window的过程

handleMessage 方法

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handleLaunchActivity方法

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handleResumeActivity方法（这个方法已经和Activity的生命周期关联了）

final void handleResumeActivity(IBinder token,
            boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
        ActivityClientRecord r = mActivities.get(token);
           //删除无用的代码
            if (r.window == null && !a.mFinished && willBeVisible) {
                r.window = r.activity.getWindow();
                View decor = r.window.getDecorView();
                decor.setVisibility(View.INVISIBLE);
                ViewManager wm = a.getWindowManager();
                WindowManager.LayoutParams l = r.window.getAttributes();
                a.mDecor = decor;
                l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
                l.softInputMode |= forwardBit;
                if (r.mPreserveWindow) {
                    a.mWindowAdded = true;
                    r.mPreserveWindow = false;
                    // Normally the ViewRoot sets up callbacks with the Activity
                    // in addView->ViewRootImpl#setView. If we are instead reusing
                    // the decor view we have to notify the view root that the
                    // callbacks may have changed.
                    ViewRootImpl impl = decor.getViewRootImpl();
                    if (impl != null) {
                        impl.notifyChildRebuilt();
                    }
                }
                if (a.mVisibleFromClient) {
                    if (!a.mWindowAdded) {
                        a.mWindowAdded = true;
                        wm.addView(decor, l);
                    } else {
                        // The activity will get a callback for this {@link LayoutParams} change
                        // earlier. However, at that time the decor will not be set (this is set
                        // in this method), so no action will be taken. This call ensures the
                        // callback occurs with the decor set.
                        a.onWindowAttributesChanged(l);
                    }
                }
            } 
    }

我们看这一句代码

wm.addView(decor, l);

这里的 wm是一个 ViewManager

 ViewManager wm = a.getWindowManager();

我们发现ViewManager 是一个接口

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因为是一个接口所以我们要找到其实现类

ViewManager wm = a.getWindowManager();

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我们通过上一篇 setContentView https://www.jianshu.com/p/1c65fd8a1de4 的了解知道 Window有一个唯一的实现类是 PhoneWindow 是因这里的mWindow就是一个Window 所以我们要找一下 PhoneWindow的 getWindowManager

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我们发现走着走着又到Window里面了

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也就是说 wm.addView 其实是 WindowManagerImpl 在addView

 wm.addView(decor, l);

WindowManagerImpl 的addView

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注意这行代码

 mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);

mGlobal 是 WindowManagerGlobal

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为了防止干扰我删除一些代码

 public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
       
        ViewRootImpl root;
        View panelParentView = null;
            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;
            }
        }
    }

注意 parentWindow 就是一个Window