一步步追踪Dialog的创建流程（一）

一直想搞明白Dialog到底是怎么创建的，今天有点时间，追踪一下Dialog的创建过程。由于能力有限，具体的实现细节不做分析，主要是搞懂代码调用的流程，从new Diaolg到Dialog显示的屏幕上的调用关系。以下便从Dialog的构造函数入手，开始一步步追踪Dialog的创建流程。

一.Dialog的构造函数

从构造函数出发，所有的构造函数都会调用下面这个构造函数：

   public Dialog(Context context, int theme) {this(context, theme, true);}Dialog(Context context, int theme, boolean createContextThemeWrapper) {if (createContextThemeWrapper) {if (theme == 0) {TypedValue outValue = new TypedValue();context.getTheme().resolveAttribute(com.android.internal.R.attr.dialogTheme,outValue, true);theme = outValue.resourceId;}mContext = new ContextThemeWrapper(context, theme);} else {mContext = context;}mWindowManager = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);Window w = PolicyManager.makeNewWindow(mContext);mWindow = w;w.setCallback(this);w.setOnWindowDismissedCallback(this);w.setWindowManager(mWindowManager, null, null);w.setGravity(Gravity.CENTER);mListenersHandler = new ListenersHandler(this);}

剔除不重要的，这里面只有两样东西特别重要，mWindowManger和mWindow。它们分别是窗口管理类和代表一个窗口的类。创建mWindow使用的是PolicyManager这个类，这个类在android api中并没有，是一个系统级别的类。所以想使用这个类创建一个window,然后自己去做一个Dialog是比较困难的。暂时不想这些，那么想想代表这个窗口的类（Window）是什么样的？mWindowManager又是怎么管理窗口的呢？带着问题，继续追踪代码。先看看mWindow到底是个什么东西。

二.Window和PhoneWindow

对于Window这个类，先看看它的注释：

/*** Abstract base class for a top-level window look and behavior policy.  An* instance of this class should be used as the top-level view added to the* window manager. It provides standard UI policies such as a background, title* area, default key processing, etc.** <p>The only existing implementation of this abstract class is* android.policy.PhoneWindow, which you should instantiate when needing a* Window.  Eventually that class will be refactored and a factory method* added for creating Window instances without knowing about a particular* implementation.*/

这段话的意思是说：Window类是一个抽象顶层窗口外观和行为策略的抽象类。这个类的实例应该作为定层的view加入到window manager中.Window提供了标准的UI策略，比如背景，标题区域，默认的按键处理等等。

这个类的唯一实例就是PhoneWindow,当我们需要一个Window时，PhoneWindow应该被实例化。最终，这个类将会被重构，并且加入一个工厂方法，用来创建一个window的实例，这样就遮蔽了创建这个类的具体细节。

接下来看看PhoneWindow,这个Window的唯一实现类，是怎样实现UI的外观绘制与事件处理的。

下面是它的构造函数：

    public PhoneWindow(Context context) {super(context);mLayoutInflater = LayoutInflater.from(context);}

构造函数获得了一个LayoutInflater的实例，这个实例用于构造一个view，因此可以猜测PhoneWindow中肯定会构造某个view.

看完了构造函数该看什么了呢？这个类有很多很多函数，总不能通通看一遍吧？这个时候，没有思路了还得回过头看Dialog类，看它是怎么把一个Dialog显示出来的。

三.show（）方法

想想我们是怎么使用Dilog的，一般创建一个Dilog对象，设置一堆东西，不管设置什么，最终要调用show()方法，不然Dialog就不会显示，所以，秘密似乎在show()方法中。

那么，show方法都做了什么呢？

    /*** 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)) {final ApplicationInfo info = mContext.getApplicationInfo();mWindow.setDefaultIcon(info.icon);mWindow.setDefaultLogo(info.logo);mActionBar = new WindowDecorActionBar(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 {}}

代码比较多，抓住主干：1.从mWindow中获得一个DecorView对象。2.使用WindowManager的addView()方法添加DecorView。那么，这个DecorView又是什么呢？

四.DecorView

DecorView的定义如下：

    private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {

从DecorVeiw的定义上就可以看到，它继承了FrameLayout,也就是说它是一个View.第三步show()方法中，DecorView首次被WindowManager添加，是不是意味着DecorView就是Window的根View呢？应该是的，不然，还能有谁？DecorView这里不做过多的分析，毕竟，我想弄明白的是Dialog创建到显示出来的过程。

五.mWindowManager,addView(...)到底做了什么？

    @Overridepublic void addView(View view, ViewGroup.LayoutParams params) {mGlobal.addView(view, params, mDisplay, mParentWindow);}

可以看到它又调用了mGlobal的addview(...)方法，这个方法是这样的：

    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 and we're running on L or above (or in the// system context), assume we want hardware acceleration.final Context context = view.getContext();if (context != null&& context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.LOLLIPOP) {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);}}}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 thingstry {root.setView(view, wparams, panelParentView);} catch (RuntimeException e) {// BadTokenException or InvalidDisplayException, clean up.synchronized (mLock) {final int index = findViewLocked(view, false);if (index >= 0) {removeViewLocked(index, true);}}throw e;}}

这个方法比较复杂了，虽然代码很长，但是它做的事情并不复杂，它不管前面做什么，最后，它是吧view,root,和wparams都加入到对应的数据结构中了。view就是Dialog中传下来的DecorView,wparams就是我们传下来的另一个参数，这里又做了一下处理。

这三个数据结构分别为:

    private final ArrayList<View> mViews = new ArrayList<View>();private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();private final ArrayList<WindowManager.LayoutParams> mParams =new ArrayList<WindowManager.LayoutParams>();

这里有出现了另一个看似很重的东西，就是root,它是ViewRootImpl的实例。那么ViewRootImpl又是干什么的呢？先了解一下，然后后面用到它的时候再仔细分析。

root,view,mParams三个肯定有联系的，最后的

root.setView(view, wparams, panelParentView);

函数同时用到了这三个，这个函数可定是建立三者联系的。所以这个方法要着重分析。在分析这个方法之前，先对ViewRootImpl，WindowSession有个感性的认识。

六.ViewRootImpl

它的构造函数如下：

   public ViewRootImpl(Context context, Display display) {mContext = context;mWindowSession = WindowManagerGlobal.getWindowSession();mDisplay = display;mBasePackageName = context.getBasePackageName();mDisplayAdjustments = display.getDisplayAdjustments();mThread = Thread.currentThread();mLocation = new WindowLeaked(null);mLocation.fillInStackTrace();mWidth = -1;mHeight = -1;mDirty = new Rect();mTempRect = new Rect();mVisRect = new Rect();mWinFrame = new Rect();mWindow = new W(this);mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;mViewVisibility = View.GONE;mTransparentRegion = new Region();mPreviousTransparentRegion = new Region();mFirst = true; // true for the first time the view is addedmAdded = false;mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this);mAccessibilityManager = AccessibilityManager.getInstance(context);mAccessibilityInteractionConnectionManager =new AccessibilityInteractionConnectionManager();mAccessibilityManager.addAccessibilityStateChangeListener(mAccessibilityInteractionConnectionManager);mHighContrastTextManager = new HighContrastTextManager();mAccessibilityManager.addHighTextContrastStateChangeListener(mHighContrastTextManager);mViewConfiguration = ViewConfiguration.get(context);mDensity = context.getResources().getDisplayMetrics().densityDpi;mNoncompatDensity = context.getResources().getDisplayMetrics().noncompatDensityDpi;mFallbackEventHandler = PolicyManager.makeNewFallbackEventHandler(context);mChoreographer = Choreographer.getInstance();mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);loadSystemProperties();mWindowIsRound = context.getResources().getBoolean(com.android.internal.R.bool.config_windowIsRound);}

构造函数里面获得了一个IWindowSession的实例，这个类又是干什么的？？？？

七.IWindowSession

IWindowSession是一个接口，它的实现类是Session,Session的定义如下：

final class Session extends IWindowSession.Stub

可以看到它是一个binder类，可定用来和Service通信的。就这样了解下就好了，不能丢了主干。

八.root.setView(view, wparams, panelParentView)

又回到这个方法，看看这个方法到底做了什么：

    /*** We have one child*/public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {synchronized (this) {if (mView == null) {mView = view;
<span style="white-space:pre">     </span>...// 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.requestLayout();

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

<span style="white-space:pre">       try {mOrigWindowType = mWindowAttributes.type;mAttachInfo.mRecomputeGlobalAttributes = true;collectViewAttributes();res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,getHostVisibility(), mDisplay.getDisplayId(),mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mInputChannel);} catch (RemoteException e) {mAdded = false;mView = null;mAttachInfo.mRootView = null;mInputChannel = null;mFallbackEventHandler.setView(null);unscheduleTraversals();setAccessibilityFocus(null, null);throw new RuntimeException("Adding window failed", e);} finally {if (restore) {attrs.restore();}}</span>}}}

这个函数很长，主要的步骤是调用了requestLayout();这里对调用requestLayout做了说明：在加入到windowManager之前，第一调用layout.为了确保收到任何系统其它事件之前做relayout.之后使用了mWindowSession.addToDisplay方法。mWindowSession实际上是一个Session的实例，addToDisplay方法如下：

    @Overridepublic int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets,InputChannel outInputChannel) {return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,outContentInsets, outStableInsets, outInputChannel);}

可以看到这里调用了mService.addWindow，这里明显是一个进程通信了，mService是WindowManagerService的实例，也就是说真正window的添加实际上在WindowManagerService中完成。

九.临时的小结

夜已经深了，劳累了一天，倦意已经溢了出来，是睡觉的时候了，明天还有早起上班。暂且分析到这里了，通过这些追踪，至少可以得出以下结论：

1.DecorView是根View.

2.ViewRootImpl中的setView方法使得DecorView和ViewRootImpl紧密相关。

3.WindowManagerService中的addWindow最终实现了Window的添加。

目前应该追踪到了开始要绘制view树的地方了，具体怎么绘制的，应该还有很长的代码要追踪，这一部分就放到下一节来探索吧。

最后，这是我首次尝试分析这部分代码，分析的比较粗糙，也可能有些地方不对，希望大家指正出来。