关于Window和WindowManager的一点愚见（添加，删除，更新）

正文

先看看自己要编写一个WindowManager该如何实现。
先看看MainActivity.java

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button)findViewById(R.id.floatbutton);
        windowManager = (WindowManager)getSystemService(Context.WINDOW_SERVICE);
        button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                createWindowManager();
            }
        });
    }

    private void createWindowManager(){
        //实现浮窗型Button
        floatButton = new Button(this);
        floatButton.setText("button");
        //view的LayoutParams
        layoutParams = new WindowManager.LayoutParams(
                LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT,0,0,PixelFormat.TRANSPARENT);
        //布局参数
        layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                | LayoutParams.FLAG_NOT_FOCUSABLE
                | LayoutParams.FLAG_SHOW_WHEN_LOCKED;
        layoutParams.gravity = Gravity.LEFT | Gravity.TOP;
        layoutParams.x = 300;
        layoutParams.y = 300;
        layoutParams.type = LayoutParams.TYPE_SYSTEM_ERROR;
        //添加view到windowmanager
        windowManager.addView(floatButton, layoutParams);
        //随着触碰改变button的位置
        floatButton.setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View av, MotionEvent ev) {
                // TODO Auto-generated method stub
                int rawX = (int)ev.getRawX();
                int rawY = (int)ev.getRawY();
                switch (ev.getAction()) {
                case MotionEvent.ACTION_MOVE:
                    layoutParams.x = rawX;
                    layoutParams.y = rawY;
                    windowManager.updateViewLayout(floatButton, layoutParams);
                    break;

                default:
                    break;
                }
                return false;
            }
        });
    }

从上面的简单范例，我们可以知道我们先要通过windowManager = (WindowManager)getSystemService(Context.WINDOW_SERVICE);来获取WindowManager的实例，看看源码在Activty.java：

@Override
    public Object getSystemService(@ServiceName @NonNull String name) {
        if (getBaseContext() == null) {
            throw new IllegalStateException(
                    "System services not available to Activities before onCreate()");
        }

        if (WINDOW_SERVICE.equals(name)) {
            return mWindowManager;
        } else if (SEARCH_SERVICE.equals(name)) {
            ensureSearchManager();
            return mSearchManager;
        }
        return super.getSystemService(name);
    }

我们可以清晰的看到，这里的确返回了一个windowManager实例。
在上面的例子中我们先定义了即将加入到Window中的view的LayoutParams参数，而在这里LayoutParams指的是WindowManager中内部类ManagerWindow.LayoutParams。
在这里我们先说说Window中flag和type参数，这两个参数比较重要：
先说说比较常见的flag:
1.FLAG_NOT_FOCUSABLE:
表示Window不需要获得焦点，也不需要接受接受各种输入时间，此标记会同时启用FLAG_NOT_TOUCH_MODAL，最终事件会直接传递给下层具有焦点的Window。

2.FLAG_NOT_TOUCH_MODAL:
在这个模式下，系统会将当前window区域之外单击事件传递给底层的Window，当前Window区域以内的2单击事件则自己处理。这个标记十分重要，一般说都会开启这个标记。

3.FLAG_SHOW_WHEN_LOCKED
开启这个模式可以让Window显示在锁屏的界面。

接着说说Type,type参数表示Window的类型：应用Window(ApplicationWndow),子Window(SubWindow)，系统Window(SystemWindow)。

应用Window对应Activity。子Window不能单独存在，它需要附属在特定在特定父Window中，比如说常见的一些Dialog就是一个子Window。系统Window是需要声明权限才能够创建Window,比如Toast和系统状态栏都是系统Window。

在Android中Window是分层的，每个Window都对应这z-ordered，层级大的会覆盖层级小的上满，写过HTML的朋友一定能明白，这个和HTML中z-index的概念一致。

在三种Window中，应用Window的层级范围是1~99，子window的层级范围1000~1999，系统Window层级是2000~2999.这些层级范围对应着WindowManager.LayoutParams的type系数。

  public static final int FIRST_APPLICATION_WINDOW = 1;

        /**
         * Window type: an application window that serves as the "base" window
         * of the overall application; all other application windows will
         * appear on top of it.
         * In multiuser systems shows only on the owning user's window.
         */
        public static final int TYPE_BASE_APPLICATION   = 1;

        /**
         * Window type: a normal application window.  The {@link #token} must be
         * an Activity token identifying who the window belongs to.
         * In multiuser systems shows only on the owning user's window.
         */
        public static final int TYPE_APPLICATION        = 2;

        /**
         * Window type: special application window that is displayed while the
         * application is starting.  Not for use by applications themselves;
         * this is used by the system to display something until the
         * application can show its own windows.
         * In multiuser systems shows on all users' windows.
         */
        public static final int TYPE_APPLICATION_STARTING = 3;

        /**
         * End of types of application windows.
         */
        public static final int LAST_APPLICATION_WINDOW = 99;

        /**
         * Start of types of sub-windows.  The {@link #token} of these windows
         * must be set to the window they are attached to.  These types of
         * windows are kept next to their attached window in Z-order, and their
         * coordinate space is relative to their attached window.
         */
        public static final int FIRST_SUB_WINDOW        = 1000;

        /**
         * Window type: a panel on top of an application window.  These windows
         * appear on top of their attached window.
         */
        public static final int TYPE_APPLICATION_PANEL  = FIRST_SUB_WINDOW;

        /**
         * Window type: window for showing media (such as video).  These windows
         * are displayed behind their attached window.
         */
        public static final int TYPE_APPLICATION_MEDIA  = FIRST_SUB_WINDOW+1;
                public static final int LAST_SUB_WINDOW         = 1999;

        /**
         * Start of system-specific window types.  These are not normally
         * created by applications.
         */
        public static final int FIRST_SYSTEM_WINDOW     = 2000;

源码也是像Android文档中那般定义。

这里要注意的当我们使用系统Window的时候必须声明权限，不然会报如下错误：

android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRootImpl$W@41a1be70 -- permission denied for this window type

我们设定为系统Window的时候，需要将type设置为TYPE_SYSTEM_OVERLAY或者TYPE_SYSTEM_ERROR。如果调用TYPE_SYSTEM_ERROR我们需要声明权限：

这样就能完成一次系统Window的创建了。

我们来看看WindowManager中在整个Window的添加，移除，更新扮演了一个什么角色。

public interface WindowManager extends ViewManager 

从上面的源码所示，WindowManager是一个继承了ViewManager接口的接口。而ViewManager中很简单，只有添加，删除，更新三个抽象方法。

public interface ViewManager
{
    /**
     * Assign the passed LayoutParams to the passed View and add the view to the window.
     * 
Throws {@link android.view.WindowManager.BadTokenException} for certain programming
     * errors, such as adding a second view to a window without removing the first view.
     * 
Throws {@link android.view.WindowManager.InvalidDisplayException} if the window is on a
     * secondary {@link Display} and the specified display can't be found
     * (see {@link android.app.Presentation}).
     * @param view The view to be added to this window.
     * @param params The LayoutParams to assign to view.
     */
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}

Window的添加，删除，更新三个动作

Window是一个抽象的概念，每一个Window都对应一个View一个ViewRootImpl，Window和View是通过ViewRootImpl联系起来的。会自定义View的朋友应该都知道，ViewRootImpl才是一个View真正实现的动作。同理在WindowManager中也是一个WindowManagerImpl作为实现的类。

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

    @Override
    public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
        mGlobal.updateViewLayout(view, params);
    }

    @Override
    public void removeView(View view) {
        mGlobal.removeView(view, false);
    }

mGlobal是指WindowManagerGlobal，这里很明显是通过了两个类的组合来控制动作，使用了桥接模式。我们先看看WindowManagerGlobal的addView方法。
首先对输入的参数进行是否合法的检验：

 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;
            }
        }

接着创建ViewRootImpl并将View添加到列表中，同时初始化重要的了表，将参数输入到列表中：

            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

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

再通过ViewRootImpl的setView来更新界面完成Window的添加过程：

root.setView(view, wparams, panelParentView);

ViewRootImpl.java中setView工作：

 public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
        synchronized (this) {
            if (mView == null) {
                mView = view;

                mAttachInfo.mDisplayState = mDisplay.getState();
                mDisplayManager.registerDisplayListener(mDisplayListener, mHandler);

                mViewLayoutDirectionInitial = mView.getRawLayoutDirection();
                mFallbackEventHandler.setView(view);
                mWindowAttributes.copyFrom(attrs);
                if (mWindowAttributes.packageName == null) {
                    mWindowAttributes.packageName = mBasePackageName;
                }
                attrs = mWindowAttributes;
                // Keep track of the actual window flags supplied by the client.
                mClientWindowLayoutFlags = attrs.flags;

                setAccessibilityFocus(null, null);

                if (view instanceof RootViewSurfaceTaker) {
                    mSurfaceHolderCallback =
                            ((RootViewSurfaceTaker)view).willYouTakeTheSurface();
                    if (mSurfaceHolderCallback != null) {
                        mSurfaceHolder = new TakenSurfaceHolder();
                        mSurfaceHolder.setFormat(PixelFormat.UNKNOWN);
                    }
                }

                // Compute surface insets required to draw at specified Z value.
                // TODO: Use real shadow insets for a constant max Z.
                final int surfaceInset = (int) Math.ceil(view.getZ() * 2);
                attrs.surfaceInsets.set(surfaceInset, surfaceInset, surfaceInset, surfaceInset);

                CompatibilityInfo compatibilityInfo = mDisplayAdjustments.getCompatibilityInfo();
                mTranslator = compatibilityInfo.getTranslator();
                mDisplayAdjustments.setActivityToken(attrs.token);

                // If the application owns the surface, don't enable hardware acceleration
                if (mSurfaceHolder == null) {
                    enableHardwareAcceleration(attrs);
                }

                boolean restore = false;
                if (mTranslator != null) {
                    mSurface.setCompatibilityTranslator(mTranslator);
                    restore = true;
                    attrs.backup();
                    mTranslator.translateWindowLayout(attrs);
                }
                if (DEBUG_LAYOUT) Log.d(TAG, "WindowLayout in setView:" + attrs);

                if (!compatibilityInfo.supportsScreen()) {
                    attrs.privateFlags |= WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
                    mLastInCompatMode = true;
                }

                mSoftInputMode = attrs.softInputMode;
                mWindowAttributesChanged = true;
                mWindowAttributesChangesFlag = WindowManager.LayoutParams.EVERYTHING_CHANGED;
                mAttachInfo.mRootView = view;
                mAttachInfo.mScalingRequired = mTranslator != null;
                mAttachInfo.mApplicationScale =
                        mTranslator == null ? 1.0f : mTranslator.applicationScale;
                if (panelParentView != null) {
                    mAttachInfo.mPanelParentWindowToken
                            = panelParentView.getApplicationWindowToken();
                }
                mAdded = true;
                int res; /* = WindowManagerImpl.ADD_OKAY; */

                // 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();
                if ((mWindowAttributes.inputFeatures
                        & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
                    mInputChannel = new InputChannel();
                }
                try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, 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();
                    }
                }

                if (mTranslator != null) {
                    mTranslator.translateRectInScreenToAppWindow(mAttachInfo.mContentInsets);
                }
                mPendingOverscanInsets.set(0, 0, 0, 0);
                mPendingContentInsets.set(mAttachInfo.mContentInsets);
                mPendingStableInsets.set(mAttachInfo.mStableInsets);
                mPendingVisibleInsets.set(0, 0, 0, 0);
                if (DEBUG_LAYOUT) Log.v(TAG, "Added window " + mWindow);
                if (res < WindowManagerGlobal.ADD_OKAY) {
                    mAttachInfo.mRootView = null;
                    mAdded = false;
                    mFallbackEventHandler.setView(null);
                    unscheduleTraversals();
                    setAccessibilityFocus(null, null);
                    switch (res) {
                        case WindowManagerGlobal.ADD_BAD_APP_TOKEN:
                        case WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN:
                            throw new WindowManager.BadTokenException(
                                "Unable to add window -- token " + attrs.token
                                + " is not valid; is your activity running?");
                        case WindowManagerGlobal.ADD_NOT_APP_TOKEN:
                            throw new WindowManager.BadTokenException(
                                "Unable to add window -- token " + attrs.token
                                + " is not for an application");
                        case WindowManagerGlobal.ADD_APP_EXITING:
                            throw new WindowManager.BadTokenException(
                                "Unable to add window -- app for token " + attrs.token
                                + " is exiting");
                        case WindowManagerGlobal.ADD_DUPLICATE_ADD:
                            throw new WindowManager.BadTokenException(
                                "Unable to add window -- window " + mWindow
                                + " has already been added");
                        case WindowManagerGlobal.ADD_STARTING_NOT_NEEDED:
                            // Silently ignore -- we would have just removed it
                            // right away, anyway.
                            return;
                        case WindowManagerGlobal.ADD_MULTIPLE_SINGLETON:
                            throw new WindowManager.BadTokenException(
                                "Unable to add window " + mWindow +
                                " -- another window of this type already exists");
                        case WindowManagerGlobal.ADD_PERMISSION_DENIED:
                            throw new WindowManager.BadTokenException(
                                "Unable to add window " + mWindow +
                                " -- permission denied for this window type");
                        case WindowManagerGlobal.ADD_INVALID_DISPLAY:
                            throw new WindowManager.InvalidDisplayException(
                                "Unable to add window " + mWindow +
                                " -- the specified display can not be found");
                    }
                    throw new RuntimeException(
                        "Unable to add window -- unknown error code " + res);
                }

                if (view instanceof RootViewSurfaceTaker) {
                    mInputQueueCallback =
                        ((RootViewSurfaceTaker)view).willYouTakeTheInputQueue();
                }
                if (mInputChannel != null) {
                    if (mInputQueueCallback != null) {
                        mInputQueue = new InputQueue();
                        mInputQueueCallback.onInputQueueCreated(mInputQueue);
                    }
                    mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                            Looper.myLooper());
                }

                view.assignParent(this);
                mAddedTouchMode = (res & WindowManagerGlobal.ADD_FLAG_IN_TOUCH_MODE) != 0;
                mAppVisible = (res & WindowManagerGlobal.ADD_FLAG_APP_VISIBLE) != 0;

                if (mAccessibilityManager.isEnabled()) {
                    mAccessibilityInteractionConnectionManager.ensureConnection();
                }

                if (view.getImportantForAccessibility() == View.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
                    view.setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_YES);
                }

                // Set up the input pipeline.
                CharSequence counterSuffix = attrs.getTitle();
                mSyntheticInputStage = new SyntheticInputStage();
                InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
                InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,
                        "aq:native-post-ime:" + counterSuffix);
                InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
                InputStage imeStage = new ImeInputStage(earlyPostImeStage,
                        "aq:ime:" + counterSuffix);
                InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
                InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,
                        "aq:native-pre-ime:" + counterSuffix);

                mFirstInputStage = nativePreImeStage;
                mFirstPostImeInputStage = earlyPostImeStage;
                mPendingInputEventQueueLengthCounterName = "aq:pending:" + counterSuffix;
            }
        }
    }

setView完成的工作很多,如声明输入事件的管道，DisplayManager的注册，view的绘画，window的添加等等，其实最重要的方法如下两个：
1.

//绘制view的入口
requestLayout();

2.通过WindowSession来完成Window的添加过程下面代码中，是一个IPC的过程。

try {
                    mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, 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();
                    }
                }

mWindowSession是一个IWindowSession，是一个Binder对象，真正实现的地方是Session。

我们看看Session.java:

final class Session extends IWindowSession.Stub

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

在这里面调用了WindowManagerService中addWindow的方法，这里就将Window的添加请求交给了WindowManagerService了：

public int addWindow(Session session, IWindow client, int seq,
            WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
            Rect outContentInsets, InputChannel outInputChannel) {
        int[] appOp = new int[1];
        //检查Permission是否合法
        int res = mPolicy.checkAddPermission(attrs, appOp);
        if (res != WindowManagerGlobal.ADD_OKAY) {
            return res;
        }

        boolean reportNewConfig = false;
        WindowState attachedWindow = null;
        WindowState win = null;
        long origId;
        final int type = attrs.type;

        synchronized(mWindowMap) {
            if (!mDisplayReady) {
                throw new IllegalStateException("Display has not been initialialized");
            }

            final DisplayContent displayContent = getDisplayContentLocked(displayId);
            if (displayContent == null) {
                Slog.w(TAG, "Attempted to add window to a display that does not exist: "
                        + displayId + ".  Aborting.");
                return WindowManagerGlobal.ADD_INVALID_DISPLAY;
            }
            if (!displayContent.hasAccess(session.mUid)) {
                Slog.w(TAG, "Attempted to add window to a display for which the application "
                        + "does not have access: " + displayId + ".  Aborting.");
                return WindowManagerGlobal.ADD_INVALID_DISPLAY;
            }

            if (mWindowMap.containsKey(client.asBinder())) {
                Slog.w(TAG, "Window " + client + " is already added");
                return WindowManagerGlobal.ADD_DUPLICATE_ADD;
            }

            if (type >= FIRST_SUB_WINDOW && type <= LAST_SUB_WINDOW) {
                attachedWindow = windowForClientLocked(null, attrs.token, false);
                if (attachedWindow == null) {
                    Slog.w(TAG, "Attempted to add window with token that is not a window: "
                          + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN;
                }
                if (attachedWindow.mAttrs.type >= FIRST_SUB_WINDOW
                        && attachedWindow.mAttrs.type <= LAST_SUB_WINDOW) {
                    Slog.w(TAG, "Attempted to add window with token that is a sub-window: "
                            + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN;
                }
            }

            if (type == TYPE_PRIVATE_PRESENTATION && !displayContent.isPrivate()) {
                Slog.w(TAG, "Attempted to add private presentation window to a non-private display.  Aborting.");
                return WindowManagerGlobal.ADD_PERMISSION_DENIED;
            }

            boolean addToken = false;
            WindowToken token = mTokenMap.get(attrs.token);
            if (token == null) {
                if (type >= FIRST_APPLICATION_WINDOW && type <= LAST_APPLICATION_WINDOW) {
                    Slog.w(TAG, "Attempted to add application window with unknown token "
                          + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
                if (type == TYPE_INPUT_METHOD) {
                    Slog.w(TAG, "Attempted to add input method window with unknown token "
                          + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
                if (type == TYPE_VOICE_INTERACTION) {
                    Slog.w(TAG, "Attempted to add voice interaction window with unknown token "
                          + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
                if (type == TYPE_WALLPAPER) {
                    Slog.w(TAG, "Attempted to add wallpaper window with unknown token "
                          + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
                if (type == TYPE_DREAM) {
                    Slog.w(TAG, "Attempted to add Dream window with unknown token "
                          + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
                token = new WindowToken(this, attrs.token, -1, false);
                addToken = true;
            } else if (type >= FIRST_APPLICATION_WINDOW && type <= LAST_APPLICATION_WINDOW) {
                AppWindowToken atoken = token.appWindowToken;
                if (atoken == null) {
                    Slog.w(TAG, "Attempted to add window with non-application token "
                          + token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_NOT_APP_TOKEN;
                } else if (atoken.removed) {
                    Slog.w(TAG, "Attempted to add window with exiting application token "
                          + token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_APP_EXITING;
                }
                if (type == TYPE_APPLICATION_STARTING && atoken.firstWindowDrawn) {
                    // No need for this guy!
                    if (localLOGV) Slog.v(
                            TAG, "**** NO NEED TO START: " + attrs.getTitle());
                    return WindowManagerGlobal.ADD_STARTING_NOT_NEEDED;
                }
            } else if (type == TYPE_INPUT_METHOD) {
                if (token.windowType != TYPE_INPUT_METHOD) {
                    Slog.w(TAG, "Attempted to add input method window with bad token "
                            + attrs.token + ".  Aborting.");
                      return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
            } else if (type == TYPE_VOICE_INTERACTION) {
                if (token.windowType != TYPE_VOICE_INTERACTION) {
                    Slog.w(TAG, "Attempted to add voice interaction window with bad token "
                            + attrs.token + ".  Aborting.");
                      return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
            } else if (type == TYPE_WALLPAPER) {
                if (token.windowType != TYPE_WALLPAPER) {
                    Slog.w(TAG, "Attempted to add wallpaper window with bad token "
                            + attrs.token + ".  Aborting.");
                      return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
            } else if (type == TYPE_DREAM) {
                if (token.windowType != TYPE_DREAM) {
                    Slog.w(TAG, "Attempted to add Dream window with bad token "
                            + attrs.token + ".  Aborting.");
                      return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
            } else if (token.appWindowToken != null) {
                Slog.w(TAG, "Non-null appWindowToken for system window of type=" + type);
                // It is not valid to use an app token with other system types; we will
                // instead make a new token for it (as if null had been passed in for the token).
                attrs.token = null;
                token = new WindowToken(this, null, -1, false);
                addToken = true;
            }

            win = new WindowState(this, session, client, token,
                    attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);
            if (win.mDeathRecipient == null) {
                // Client has apparently died, so there is no reason to
                // continue.
                Slog.w(TAG, "Adding window client " + client.asBinder()
                        + " that is dead, aborting.");
                return WindowManagerGlobal.ADD_APP_EXITING;
            }

            if (win.getDisplayContent() == null) {
                Slog.w(TAG, "Adding window to Display that has been removed.");
                return WindowManagerGlobal.ADD_INVALID_DISPLAY;
            }

            mPolicy.adjustWindowParamsLw(win.mAttrs);
            win.setShowToOwnerOnlyLocked(mPolicy.checkShowToOwnerOnly(attrs));

            res = mPolicy.prepareAddWindowLw(win, attrs);
            if (res != WindowManagerGlobal.ADD_OKAY) {
                return res;
            }

            if (outInputChannel != null && (attrs.inputFeatures
                    & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
                String name = win.makeInputChannelName();
                InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
                win.setInputChannel(inputChannels[0]);
                inputChannels[1].transferTo(outInputChannel);

                mInputManager.registerInputChannel(win.mInputChannel, win.mInputWindowHandle);
            }

            // From now on, no exceptions or errors allowed!

            res = WindowManagerGlobal.ADD_OKAY;

            origId = Binder.clearCallingIdentity();

            if (addToken) {
                mTokenMap.put(attrs.token, token);
            }
            win.attach();
            mWindowMap.put(client.asBinder(), win);
            if (win.mAppOp != AppOpsManager.OP_NONE) {
                if (mAppOps.startOpNoThrow(win.mAppOp, win.getOwningUid(), win.getOwningPackage())
                        != AppOpsManager.MODE_ALLOWED) {
                    win.setAppOpVisibilityLw(false);
                }
            }

            if (type == TYPE_APPLICATION_STARTING && token.appWindowToken != null) {
                token.appWindowToken.startingWindow = win;
                if (DEBUG_STARTING_WINDOW) Slog.v (TAG, "addWindow: " + token.appWindowToken
                        + " startingWindow=" + win);
            }

            boolean imMayMove = true;

            if (type == TYPE_INPUT_METHOD) {
                win.mGivenInsetsPending = true;
                mInputMethodWindow = win;
                addInputMethodWindowToListLocked(win);
                imMayMove = false;
            } else if (type == TYPE_INPUT_METHOD_DIALOG) {
                mInputMethodDialogs.add(win);
                addWindowToListInOrderLocked(win, true);
                moveInputMethodDialogsLocked(findDesiredInputMethodWindowIndexLocked(true));
                imMayMove = false;
            } else {
                addWindowToListInOrderLocked(win, true);
                if (type == TYPE_WALLPAPER) {
                    mLastWallpaperTimeoutTime = 0;
                    displayContent.pendingLayoutChanges |= FINISH_LAYOUT_REDO_WALLPAPER;
                } else if ((attrs.flags&FLAG_SHOW_WALLPAPER) != 0) {
                    displayContent.pendingLayoutChanges |= FINISH_LAYOUT_REDO_WALLPAPER;
                } else if (mWallpaperTarget != null
                        && mWallpaperTarget.mLayer >= win.mBaseLayer) {
                    // If there is currently a wallpaper being shown, and
                    // the base layer of the new window is below the current
                    // layer of the target window, then adjust the wallpaper.
                    // This is to avoid a new window being placed between the
                    // wallpaper and its target.
                    displayContent.pendingLayoutChanges |= FINISH_LAYOUT_REDO_WALLPAPER;
                }
            }

            win.mWinAnimator.mEnterAnimationPending = true;

            if (displayContent.isDefaultDisplay) {
                mPolicy.getContentInsetHintLw(attrs, outContentInsets);
            } else {
                outContentInsets.setEmpty();
            }

            if (mInTouchMode) {
                res |= WindowManagerGlobal.ADD_FLAG_IN_TOUCH_MODE;
            }
            if (win.mAppToken == null || !win.mAppToken.clientHidden) {
                res |= WindowManagerGlobal.ADD_FLAG_APP_VISIBLE;
            }

            mInputMonitor.setUpdateInputWindowsNeededLw();

            boolean focusChanged = false;
            if (win.canReceiveKeys()) {
                focusChanged = updateFocusedWindowLocked(UPDATE_FOCUS_WILL_ASSIGN_LAYERS,
                        false /*updateInputWindows*/);
                if (focusChanged) {
                    imMayMove = false;
                }
            }

            if (imMayMove) {
                moveInputMethodWindowsIfNeededLocked(false);
            }

            assignLayersLocked(displayContent.getWindowList());
            // Don't do layout here, the window must call
            // relayout to be displayed, so we'll do it there.

            if (focusChanged) {
                mInputMonitor.setInputFocusLw(mCurrentFocus, false /*updateInputWindows*/);
            }
            mInputMonitor.updateInputWindowsLw(false /*force*/);

            if (localLOGV) Slog.v(
                TAG, "New client " + client.asBinder()
                + ": window=" + win);

            if (win.isVisibleOrAdding() && updateOrientationFromAppTokensLocked(false)) {
                reportNewConfig = true;
            }
        }

        if (reportNewConfig) {
            sendNewConfiguration();
        }

        Binder.restoreCallingIdentity(origId);

        return res;
    }

大致的工作有如下几点：检查在xml中是否声明好权限，接着判断是哪个层级的Window，再判断之前在WindowMananger.LayoutParms中的参数，还有对应错误的type等并作出相应的异常处理，添加window到列表中，加入事件的分发机制等等。

Window的删除动作：
同上面的思路·一样是在WindowGlobal的removeview中实现：

public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }

            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }
     private int findViewLocked(View view, boolean required) {
        final int index = mViews.indexOf(view);
        if (required && index < 0) {
            throw new IllegalArgumentException("View=" + view + " not attached to window manager");
        }
        return index;
    }

这里的逻辑就很清晰，是通过 findViewLocked来查找之前初始化好的mView的list中对应View的索引，再调用removeViewLocked来删除。

private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();

        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }

在这里同样还是通过ViewRootImpl中完成删除的。注意WindowManager中还提供了removeviewimmediate这种同步删除机制， 为了避免出现意外错误请将imm为判断为false。我们看看ViewRootImpl中die方法：

boolean die(boolean immediate) {
        // Make sure we do execute immediately if we are in the middle of a traversal or the damage
        // done by dispatchDetachedFromWindow will cause havoc on return.
        if (immediate && !mIsInTraversal) {
            doDie();
            return false;
        }

        if (!mIsDrawing) {
            destroyHardwareRenderer();
        } else {
            Log.e(TAG, "Attempting to destroy the window while drawing!\n" +
                    "  window=" + this + ", title=" + mWindowAttributes.getTitle());
        }
        mHandler.sendEmptyMessage(MSG_DIE);
        return true;
    }

在die方法中只做了简单的判断，如果是接着通过发送信息给Handler去调用doDie方法，真正的逻辑是在里面的 dispatchDetachedFromWindow();完成的。

void doDie() {
        checkThread();
        if (LOCAL_LOGV) Log.v(TAG, "DIE in " + this + " of " + mSurface);
        synchronized (this) {
            if (mRemoved) {
                return;
            }
            mRemoved = true;
            if (mAdded) {
                dispatchDetachedFromWindow();
            }

            if (mAdded && !mFirst) {
                destroyHardwareRenderer();

                if (mView != null) {
                    int viewVisibility = mView.getVisibility();
                    boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
                    if (mWindowAttributesChanged || viewVisibilityChanged) {
                        // If layout params have been changed, first give them
                        // to the window manager to make sure it has the correct
                        // animation info.
                        try {
                            if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
                                    & WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
                                mWindowSession.finishDrawing(mWindow);
                            }
                        } catch (RemoteException e) {
                        }
                    }

                    mSurface.release();
                }
            }

            mAdded = false;
        }
        WindowManagerGlobal.getInstance().doRemoveView(this);
    }

上面的方法主要完成的工作如下：垃圾回收，通过Session的Remove来移除Window，调用View的 dispatchDetachedFromWindow();方法，调用 WindowManagerGlobal.getInstance().doRemoveView(this);刷新列表中数据。

Window的更新动作：
我们继续看看WindowManagerGlobal中的update:

 public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;

        view.setLayoutParams(wparams);

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            root.setLayoutParams(wparams, false);
        }
    }

逻辑也很清晰，view调用setLayoutParams去调用ViewRootImpl中requestLayout，通过findViewLocked寻找view对应的索引，刷新view中对应的数据。

在这里可以总结为一句话，就是View是Android中的视图呈现方式，但是它不能单独存在，它必须依附在Window上。

必须一提的是：WindowManager的工作流程不仅仅只有这么一点，从添加Window的过程中我们还发现里面还涉及到了WindowState这个类,我直译为Window的状态，里面保存了Window相关的句柄（WindowToken），对应的WindowManager,Uid,WindowId,显示内容等等，这些参数主要是在ViewRootImpl中的setView方法中参与工作。