概述

window

• window 是一個抽象類，具體實現是PhoneWindow
• window 也是一個抽象的概念，每個 window 內對應這一個 DecorView 和一個 ViewRootImpl，window 和DecorView 通過ViewRootImpl聯系。

WindowManager

WindowManager 是 外界訪問 Window 的入口

WindowManagerService

window 的具體實現位于WindowManagerService中，WindowManager和WindowManagerService的交互是一個 IPC 的過程，

源碼分析

window 的添加、刪除、更新 view 均是通過WindowManager來完成的，而WindowManager繼承了 ViewManager的接口

/** Interface to let you add and remove child views to an Activity. To get an instance
  * of this class, call {@link android.content.Context#getSystemService(java.lang.String) Context.getSystemService()}.
  */
public interface ViewManager
{
    /**
     * Assign the passed LayoutParams to the passed View and add the view to the window.
     * <p>Throws {@link android.view.WindowManager.BadTokenException} for certain programming
     * errors, such as adding a second view to a window without removing the first view.
     * <p>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);
}

對應的三個方法，繼續看WindowManager對應的具體實現類，WindowManagerImple

    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.addView(view, params, mDisplay, mParentWindow);
    }
    
        @Override
    public void removeView(View view) {
        mGlobal.removeView(view, false);
    }
    
        @Override
    public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.updateViewLayout(view, params);
    }

可以看到，具體的方法均交給WindowManagerGlobal來處理，而WindowManagerGlobal則以工程模式提供了自己的實例

private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();

看看``中比較重要的幾個成員變量

    private final ArrayList<View> mViews = new ArrayList<View>();//所有 window 對應的 DecorView
    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();////所有 window 對應的 ViewRootImpl
    private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>(); //所有 window 對應的 WindowManager.LayoutParams
    private final ArraySet<View> mDyingViews = new ArraySet<View>();//所有 window 對應需要刪除的 view

添加過程

具體分析WindowManagerGlobal的addview

 public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        //首先檢查了參數，并拋出對應的異常
        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);
            }

//通過findViewLocked找到 view 對應的 index
            int index = findViewLocked(view, false);
            if (index >= 0) {
            //如果找到了，說明這個 view 已經被添加進來了
                if (mDyingViews.contains(view)) {
                //這個 view 是需要刪除的話，那么不用管直接用doDie 刪除
                    // Don't wait for MSG_DIE to make it's way through root's queue.
                    mRoots.get(index).doDie();
                } else {
                //說明這個 view 已經被添加進來了,拋出異常
                    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++) {
                //找到對應的 window
                    if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                        panelParentView = mViews.get(i);
                    }
                }
            }

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

            view.setLayoutParams(wparams);
//將得DecorView viewimpl params 都加入到 list 中
            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }

        // do this last because it fires off messages to start doing things
        try {
        //這個重要，通過 viewrootImpl 的 setview 方法來刷新 view
            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;
        }
    }

setview 的方法比較長，看其中比較重要的幾個方法
requestLayout();

    @Override
    public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            checkThread();
            mLayoutRequested = true;
            scheduleTraversals();
        }
    }

scheduleTraversals 是 view 開始繪制的入口

繼續往下看 window 的添加過程

mOrigWindowType = mWindowAttributes.type;
                    mAttachInfo.mRecomputeGlobalAttributes = true;
                    collectViewAttributes();
                    res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(),
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, mInputChannel);

IWindowSession是一個 binder 對象。最終會調用到windowManagerService中的方法

刪除過程

具體分析WindowManagerGlobal的removeview

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

        synchronized (mLock) {
       //找到對應的 index ，再removeViewLocked
            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 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());
            }
        }
//        ViewRootImpl 的 die 方法
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }
    
    //die 方法比較簡單，就是發送了一個 message，最后在處理 message 的時候調用了doDie
        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;
    }
    
    
     void doDie() {
        checkThread();
        if (LOCAL_LOGV) Log.v(TAG, "DIE in " + this + " of " + mSurface);
        synchronized (this) {
            if (mRemoved) {
                return;
            }
            mRemoved = true;
            if (mAdded) {
            //這里做了一些資源的回抽，停動畫等
                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;
        }
        //在其中清理 那些成員 list 變量
        WindowManagerGlobal.getInstance().doRemoveView(this);
    }
    
    

更新過程

 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) {
        //刪除舊的 param 更新成新的 param
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            //通過 viewrootImpl 來刷新 view
            root.setLayoutParams(wparams, false);
        }
    }

拓展閱讀 window、Activity、DecorView、ViewRoot關系

參考

http://gold.xitu.io/entry/571338c7c4c9710054cea455
http://www.lxweimin.com/p/687010ccad66