Android中Window添加View的底層原理 · android技術分享與探討

### 一，WIndow和windowManager Window是一個抽象類，它的具體實現是PhoneWindow，創建一個window很簡單，只需要創建一個windowManager即可，window具體實現在windowManagerService中，windowManager和windowManagerService的交互是一個IPC的過程。下面是用windowManager的例子: ~~~ mFloatingButton = new Button(this); mFloatingButton.setText( "window"); mLayoutParams = new WindowManager.LayoutParams( LayoutParams. WRAP_CONTENT, LayoutParams.WRAP_CONTENT, 0, 0, PixelFormat. TRANSPARENT); mLayoutParams. flags = LayoutParams.FLAG_NOT_TOUCH_MODAL | LayoutParams. FLAG_NOT_FOCUSABLE | LayoutParams. FLAG_SHOW_WHEN_LOCKED; mLayoutParams. type = LayoutParams. TYPE_SYSTEM_ERROR; mLayoutParams. gravity = Gravity. LEFT | Gravity. TOP; mLayoutParams. x = 100; mLayoutParams. y = 300; mFloatingButton.setOnTouchListener( this); mWindowManager.addView( mFloatingButton, mLayoutParams); ~~~ flags和type兩個屬性很重要，下面對一些屬性進行介紹，首先是flags： FLAG_NOT_TOUCH_MODAL表示不需要獲取焦點，也不需要接收各種輸入，最終事件直接傳遞給下層具有焦點的window。 FLAG_NOT_FOCUSABLE：在此window外的區域單擊事件傳遞到底層window中。當前的區域則自己處理，這個一般都要設置，很重要。 FLAG_SHOW_WHEN_LOCKED?：開啟可以讓window顯示在鎖屏界面上。再來看下type這個參數： window有三種類型：應用window，子window，系統window。應用類對應一個Activity，子Window不能單獨存在，需要附屬在父Window上，比如常用的Dialog。系統Window是需要聲明權限再創建的window，如toast等。 window有z-ordered屬性，層級越大，越在頂層。應用window層級1-99，子window1000-1999，系統2000-2999。這此層級對應著windowManager的type參數。系統層級常用的有兩個TYPE_SYSTEM_OVERLAY或者TYPE_SYSTEM_ERROR。比如想用TYPE_SYSTEM_ERROR，只需 mLayoutParams.type = LayoutParams.TYPE_SYSTEM_ERROR。還要添加權限。有了對window的基本認識之后，我們來看下它底層如何實現加載View的。 ### 二，window的創建。其實Window的創建跟之前我寫的一篇博客[LayoutInflater源碼分析](http://blog.csdn.net/u014486880/article/details/50707672)有點相似。Window的創建是在Activity創建的attach方法中，通過PolicyManager的makeNewWindow方法。Activity中實現了Window的Callback接口，因此當window狀態改變時就會回調Activity方法。如onAttachedToWindow等。PolicyManager的真正實現類是Policy，看下它的代碼： ~~~ public Window makeNewWindow(Context context) { return new PhoneWindow(context); } ~~~ 到此Window創建完成。下面分析view是如何附屬到window上的。看Activity的setContentView方法。 ~~~ public void setContentView(int layoutResID) { getWindow().setContentView(layoutResID); initWindowDecorActionBar(); } ~~~ 兩部分，設置內容和設置ActionBar。window的具體實現是PhoneWindow，看它的setContent。 ~~~ public void setContentView(int layoutResID) { // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window // decor, when theme attributes and the like are crystalized. Do not check the feature // before this happens. if (mContentParent == null) { installDecor(); } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, getContext()); transitionTo(newScene); } else { mLayoutInflater.inflate(layoutResID, mContentParent); } final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } } ~~~ 看到了吧，又是分析它。這里分三步執行： 1.如果沒有DecorView，在installDecor中的generateDecor()創建DecorView。之前就分析過，這次就不再分析它了。 2.將View添加到decorview中的mContentParent中。 3.回調Activity的onContentChanged接口。經過以上操作，DecorView創建了，但還沒有正式添加到Window中。在ActivityResumeActivity中首先會調用Activity的onResume，再調用Activity的makeVisible，makeVisible中真正添加view ，代碼如下： ~~~ void makeVisible() { if (!mWindowAdded) { ViewManager wm = getWindowManager(); wm.addView(mDecor, getWindow().getAttributes()); mWindowAdded = true; } mDecor.setVisibility(View.VISIBLE); } ~~~ 通過上面的addView方法將View添加到Window。 ### 三，Window操作View內部機制 ## 1.window的添加一個window對應一個view和一個viewRootImpl,window和view通過ViewRootImpl來建立聯系，它并不存在，實體是view。只能通過?windowManager來操作它。 windowManager的實現類是windowManagerImpl。它并沒有直接實現三大操作，而是委托給WindowManagerGlobal。addView的實現分為以下幾步： 1.檢查參數是否合法。 ~~~ 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; } } ~~~ 2.創建ViewRootImpl并將View添加到列表中。 ~~~ root = new ViewRootImpl(view.getContext(), display); view.setLayoutParams(wparams); mViews.add(view); mRoots.add(root); mParams.add(wparams); ~~~ 3.通過ViewRootImpl來更新界面并完成window的添加過程。 ~~~ root.setView(view, wparams, panelParentView); ~~~ 上面的root就是ViewRootImpl，setView中通過requestLayout()來完成異步刷新，看下requestLayout： ~~~ public void requestLayout() { if (!mHandlingLayoutInLayoutRequest) { checkThread(); mLayoutRequested = true; scheduleTraversals(); } } ~~~ 接下來通過WindowSession來完成window添加過程，WindowSession是一個Binder對象，真正的實現類是 Session，window的添加是一次IPC調用。 ~~~ 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); } ~~~ 在Session內部會通過WindowManagerService來實現Window的添加。 ~~~ public 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); } ~~~ 在WindowManagerService內部會為每一個應用保留一個單獨的session。 ## 2.window的刪除看下WindowManagerGlobal的removeView： ~~~ 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); } } ~~~ 首先調用findViewLocked來查找刪除view的索引，這個過程就是建立數組遍歷。然后再調用removeViewLocked來做進一步的刪除。 ~~~ 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); } } } ~~~ 真正刪除操作是viewRootImpl來完成的。windowManager提供了兩種刪除接口，removeViewImmediate，removeView。它們分別表示異步刪除和同步刪除。具體的刪除操作由ViewRootImpl的die來完成。 ~~~ 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; } ~~~ 由上可知如果是removeViewImmediate，立即調用doDie，如果是removeView，用handler發送消息，ViewRootImpl中的Handler會處理消息并調用doDie。重點看下doDie: ~~~ 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); } ~~~ 主要做四件事: 1.垃圾回收相關工作，比如清數據，回調等。 2.通過Session的remove方法刪除Window,最終調用WindowManagerService的removeWindow 3.調用dispathDetachedFromWindow，在內部會調用onDetachedFromWindow()和onDetachedFromWindowInternal()。當view移除時會調用onDetachedFromWindow，它用于作一些資源回收。 4.通過doRemoveView刷新數據，刪除相關數據，如在mRoot，mDyingViews中刪除對象等。 ~~~ void doRemoveView(ViewRootImpl root) { synchronized (mLock) { final int index = mRoots.indexOf(root); if (index >= 0) { mRoots.remove(index); mParams.remove(index); final View view = mViews.remove(index); mDyingViews.remove(view); } } if (HardwareRenderer.sTrimForeground && HardwareRenderer.isAvailable()) { doTrimForeground(); } } ~~~ ## 3.更新window 看下WindowManagerGlobal中的updateViewLayout。 ~~~ 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); } } ~~~ 通過viewRootImpl的setLayoutParams更新viewRootImpl的layoutParams,接著scheduleTraversals對view重新布局，包括測量，布局，重繪，此外它還會通過WindowSession來更新window。這個過程由WindowManagerService實現。這跟上面類似，就不再重復。到此Window底層源碼就分析完啦。