问题

在慢慢熟悉android 的过程中，发现一个view 或者layout的初始化，或者构造的流程还是比较清楚的，也就是加到父控件中，然后就开始了对应的生命周期。但是整个界面的父控件，或者说系统的第一个view， 是怎么来的，如何初始化和绘制的呢？

概述

概述：带着困扰我的问题，在前文的基础上，继续分析应用界面和framework的关系，通过分析viewrootimpl 的来源，并结合dialog, popupwindow, 和activity 的 根view的创建流程，回答了问题界面的根view 或者第一个view 是如何初始化，并加入到framework 中的。

分析viewrootimpl 的来源

本文分析是接上篇《源码分析:LayoutParams的wrap_content, match_parent, 和具体值》，在上文中简要分析了windowmanager中对界面的处理。

使用各种搜索方法，可以看到，全部android代码中只有一处引用ViewRootImpl 这个类，那就是

android.view.WindowManagerImpl.addView(View, LayoutParams, CompatibilityInfoHolder, boolean)

通过分析代码可以看到，windowmanager在addview() 的过程中，为了管理添加进来的view，使用了三个数组

    private View[] mViews;
    private ViewRootImpl[] mRoots;
    private WindowManager.LayoutParams[] mParams;

            root = new ViewRootImpl(view.getContext());
            root.mAddNesting = 1;
            if (cih == null) {
                root.mCompatibilityInfo = new CompatibilityInfoHolder();
            } else {
                root.mCompatibilityInfo = cih;
            }

            view.setLayoutParams(wparams);
            
            if (mViews == null) {
                index = 1;
                mViews = new View[1];
                mRoots = new ViewRootImpl[1];
                mParams = new WindowManager.LayoutParams[1];
            } else {
                index = mViews.length + 1;
                Object[] old = mViews;
                mViews = new View[index];
                System.arraycopy(old, 0, mViews, 0, index-1);
                old = mRoots;
                mRoots = new ViewRootImpl[index];
                System.arraycopy(old, 0, mRoots, 0, index-1);
                old = mParams;
                mParams = new WindowManager.LayoutParams[index];
                System.arraycopy(old, 0, mParams, 0, index-1);
            }
            index--;

            mViews[index] = view;
            mRoots[index] = root;
            mParams[index] = wparams;

        // do this last because it fires off messages to start doing things        root.setView(view, wparams, panelParentView);

ViewRootImpl(Context) - android.view.ViewRootImpl
	addView(View, LayoutParams, CompatibilityInfoHolder, boolean) : void - android.view.WindowManagerImpl
		addView(View, LayoutParams, CompatibilityInfoHolder) : void - android.view.WindowManagerImpl
		addView(View, LayoutParams) : void - android.view.WindowManagerImpl
			addIntruderView() : void - com.android.systemui.statusbar.phone.PhoneStatusBar
			addNavigationBar() : void - com.android.systemui.statusbar.phone.PhoneStatusBar
			addPanelWindows() : void - com.android.systemui.statusbar.tablet.TabletStatusBar (5 matches)
			addStartingWindow(IBinder, String, int, CompatibilityInfo, CharSequence, int, int, int) : View - com.android.internal.policy.impl.PhoneWindowManager
			addView(View) : void - android.view.WindowManagerImpl
			advance() : void - com.android.systemui.statusbar.tablet.TabletTicker
			handleResumeActivity(IBinder, boolean, boolean) : void - android.app.ActivityThread
			handleShow() : void - android.widget.Toast.TN
			invokePopup(LayoutParams) : void - android.widget.PopupWindow
			makeVisible() : void - android.app.Activity
			onBarViewAttached() : void - com.android.systemui.statusbar.phone.PhoneStatusBar
			onCreate() : void - com.android.systemui.LoadAverageService
			openPanel(PanelFeatureState, KeyEvent) : void - com.android.internal.policy.impl.PhoneWindow
			setVisible(boolean) : void - android.widget.ZoomButtonsController
			show() : void - android.app.Dialog
			show() : void - com.android.internal.policy.impl.KeyguardViewManager
			show(int) : void - android.widget.MediaController
			showCompatibilityHelp() : void - com.android.systemui.statusbar.tablet.TabletStatusBar
			showSafeModeOverlay() : void - com.android.server.am.ActivityManagerService
			start() : void - com.android.systemui.statusbar.StatusBar
			startAnimation(Runnable, int, int, boolean, boolean) : void - com.android.systemui.screenshot.GlobalScreenshot
			updateRecentsPanel() : void - com.android.systemui.statusbar.phone.PhoneStatusBar
			updateSettings() : void - com.android.internal.policy.impl.PhoneWindowManager

分析Dialog 是如何加入到windowmanager 的

柿子先捡软的捏， 挑个简单的先。看下show() : void - android.app.Dialog

这不就是经常调用的大名鼎鼎的show() 嘛。 dialog写完最后调用的show() 方法，没错就是它。从这个控件来看确实就是这样通过windowmanager， show 一个dialog，就是windowmanager.addview一下啦。 那么addview的时候，自然就应该是dialog的根view，父控件喽。查看一下代码验证一下我们的猜测。

    /**
     * Start the dialog and display it on screen.  The window is placed in the
     * application layer and opaque.  Note that you should not override this
     * method to do initialization when the dialog is shown, instead implement
     * that in {@link #onStart}.
     */
    public void show() {
        if (mShowing) {
            if (mDecor != null) {
                if (mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
                    mWindow.invalidatePanelMenu(Window.FEATURE_ACTION_BAR);
                }
                mDecor.setVisibility(View.VISIBLE);
            }
            return;
        }

        mCanceled = false;
        
        if (!mCreated) {
            dispatchOnCreate(null);
        }

        onStart();
        mDecor = mWindow.getDecorView();

        if (mActionBar == null && mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
            mActionBar = new ActionBarImpl(this);
        }

        WindowManager.LayoutParams l = mWindow.getAttributes();
        if ((l.softInputMode
                & WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
            WindowManager.LayoutParams nl = new WindowManager.LayoutParams();
            nl.copyFrom(l);
            nl.softInputMode |=
                    WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
            l = nl;
        }

        try {
            mWindowManager.addView(mDecor, l);
            mShowing = true;
    
            sendShowMessage();
        } finally {
        }
    }

    /**
     * Retrieve the top-level window decor view (containing the standard
     * window frame/decorations and the client's content inside of that), which
     * can be added as a window to the window manager.
     * 
     * <p><em>Note that calling this function for the first time "locks in"
     * various window characteristics as described in
     * {@link #setContentView(View, android.view.ViewGroup.LayoutParams)}.</em></p>
     * 
     * @return Returns the top-level window decor view.
     */
    public abstract View getDecorView();

接下来看下这个mDecor到底是什么。

找到具体的实现com.android.internal.policy.impl.PhoneWindow.getDecorView()

    @Override
    public final View getDecorView() {
        if (mDecor == null) {
            installDecor();
        }
        return mDecor;
    }

    private void installDecor() {
        if (mDecor == null) {
            mDecor = generateDecor();
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
        }
<span style="white-space:pre">	</span>//......
    }

    protected DecorView generateDecor() {
        return new DecorView(getContext(), -1);
    }

        public DecorView(Context context, int featureId) {
            super(context);
            mFeatureId = featureId;
        }

        /** The feature ID of the panel, or -1 if this is the application's DecorView */
        private final int mFeatureId;

    private final class DecorView extends FrameLayout implements RootViewSurfaceTaker

所以，回顾一下，这个 top-level window decor view，被add 进windowmanager 中的就是一个framelayout。

这点通过 hierarchyviewer 分析 UI 时得到印证。

如何使用，请移步官方文档《Using Hierarchy Viewer》，已经有很多人写了中文文档，不再赘述。

好了，到这里知道了系统dialog 中对应的 顶层 view 是一个framelayout， 对应到framework中 viewrootimpl 中的rootview。

同理，PopupWindow 是怎么干的

然后举一反三，看下PopupWindow 是怎么搞的。

invokePopup(LayoutParams) : void - android.widget.PopupWindow
	showAsDropDown(View, int, int) : void - android.widget.PopupWindow
	showAtLocation(IBinder, int, int, int) : void - android.widget.PopupWindow

        mWindowManager.addView(mPopupView, p);

        if (mBackground != null) {
            final ViewGroup.LayoutParams layoutParams = mContentView.getLayoutParams();
            int height = ViewGroup.LayoutParams.MATCH_PARENT;
            if (layoutParams != null &&
                    layoutParams.height == ViewGroup.LayoutParams.WRAP_CONTENT) {
                height = ViewGroup.LayoutParams.WRAP_CONTENT;
            }

            // when a background is available, we embed the content view
            // within another view that owns the background drawable
            PopupViewContainer popupViewContainer = new PopupViewContainer(mContext);
            PopupViewContainer.LayoutParams listParams = new PopupViewContainer.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT, height
            );
            popupViewContainer.setBackgroundDrawable(mBackground);
            popupViewContainer.addView(mContentView, listParams);

            mPopupView = popupViewContainer;
        } else {
            mPopupView = mContentView;

    public void setContentView(View contentView) {
        if (isShowing()) {
            return;
        }

        mContentView = contentView;

        if (mContext == null && mContentView != null) {
            mContext = mContentView.getContext();
        }

        if (mWindowManager == null && mContentView != null) {
            mWindowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
        }
    }

接下来是activity

那最常用的activity 中又是怎样的呢？

    void makeVisible() {
        if (!mWindowAdded) {
            ViewManager wm = getWindowManager();
            wm.addView(mDecor, getWindow().getAttributes());
            mWindowAdded = true;
        }
        mDecor.setVisibility(View.VISIBLE);
    }

首先扫了一下activity 这个类，发现没有赋值语句， 查看一下基类，也没有。最后查看所有mDecor 的调用。

mDecor - android.app.Activity
	dispatchKeyEvent(KeyEvent) : boolean - android.app.Activity
	handleDestroyActivity(IBinder, boolean, int, boolean) : void - android.app.ActivityThread (2 matches)
	handleResumeActivity(IBinder, boolean, boolean) : void - android.app.ActivityThread (2 matches)
	handleSendResult(ResultData) : void - android.app.ActivityThread
	handleWindowVisibility(IBinder, boolean) : void - android.app.ActivityThread
	makeVisible() : void - android.app.Activity (2 matches)
	onWindowAttributesChanged(LayoutParams) : void - android.app.Activity
	setVisible(boolean) : void - android.app.Activity
	updateVisibility(ActivityClientRecord, boolean) : void - android.app.ActivityThread

    final void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward) {
        // If we are getting ready to gc after going to the background, well
        // we are back active so skip it.
        unscheduleGcIdler();

        ActivityClientRecord r = performResumeActivity(token, clearHide);

        if (r != null) {
            final Activity a = r.activity;

            if (localLOGV) Slog.v(
                TAG, "Resume " + r + " started activity: " +
                a.mStartedActivity + ", hideForNow: " + r.hideForNow
                + ", finished: " + a.mFinished);

            final int forwardBit = isForward ?
                    WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;

            // If the window hasn't yet been added to the window manager,
            // and this guy didn't finish itself or start another activity,
            // then go ahead and add the window.
            boolean willBeVisible = !a.mStartedActivity;
            if (!willBeVisible) {
                try {
                    willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(
                            a.getActivityToken());
                } catch (RemoteException e) {
                }
            }
            if (r.window == null && !a.mFinished && willBeVisible) {
                r.window = r.activity.getWindow();
                <span style="color:#ff0000;">View decor = r.window.getDecorView();</span>
                decor.setVisibility(View.INVISIBLE);
                ViewManager wm = a.getWindowManager();
                WindowManager.LayoutParams l = r.window.getAttributes();
                <span style="color:#ff0000;">a.mDecor = decor;</span>
                l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
                l.softInputMode |= forwardBit;
                if (a.mVisibleFromClient) {
                    a.mWindowAdded = true;
                    wm.addView(decor, l);
                }

<span style="white-space:pre">		</span>//......

    }

而ActivityClientRecord r = performResumeActivity(token, clearHide);

也就是说是具体resume 的activity 的 window 的decorView()。

通过前面dialog 部分的分析，我们知道使用phoneWindow 的话，那就是framelayout 的那个 decorView。而目前还没有其他类型的window，这从window的继承关系可以看出。

在这里我们看到，activity 在resume的时候，通过判断是否要visible ，来把activity 的window 的decorView 加到windowmanager中，那么在activity的生命周期就应该在对应的状态中从windowmanager中移除该decorView。

在前面mDecor 的调用中，确实发现了在android.app.ActivityThread.handleDestroyActivity(IBinder, boolean, int, boolean)，中。

    private void handleDestroyActivity(IBinder token, boolean finishing,
            int configChanges, boolean getNonConfigInstance) {
        ActivityClientRecord r = performDestroyActivity(token, finishing,
                configChanges, getNonConfigInstance);
        if (r != null) {
            cleanUpPendingRemoveWindows(r);
            WindowManager wm = r.activity.getWindowManager();
            <span style="color:#ff0000;">View v = r.activity.mDecor;</span>
            if (v != null) {
                if (r.activity.mVisibleFromServer) {
                    mNumVisibleActivities--;
                }
                IBinder wtoken = v.getWindowToken();
                if (r.activity.mWindowAdded) {
                    if (r.onlyLocalRequest) {
                        // Hold off on removing this until the new activity's
                        // window is being added.
                        r.mPendingRemoveWindow = v;
                        r.mPendingRemoveWindowManager = wm;
                    } else {
                       <span style="color:#ff0000;"> wm.removeViewImmediate(v);</span>
                    }
                }

<span style="white-space:pre">	</span>}

<span style="white-space:pre">	</span>//......

    }

一句话结论

留的尾巴