一、WIndow和windowManager
Window是一個(gè)抽象類，它的具體實(shí)現(xiàn)是PhoneWindow，創(chuàng)建一個(gè)window很簡單，只需要?jiǎng)?chuàng)建一個(gè)windowManager即可，window具體實(shí)現(xiàn)在windowManagerService中，windowManager和windowManagerService的交互是一個(gè)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(gè)屬性很重要，下面對一些屬性進(jìn)行介紹，首先是flags：
FLAG_NOT_TOUCH_MODAL表示不需要獲取焦點(diǎn)，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(diǎn)的window。
FLAG_NOT_FOCUSABLE：在此window外的區(qū)域單擊事件傳遞到底層window中。當(dāng)前的區(qū)域則自己處理，這個(gè)一般都要設(shè)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(gè)參數(shù)：
window有三種類型：應(yīng)用window，子window，系統(tǒng)window。應(yīng)用類對應(yīng)一個(gè)Activity，子Window不能單獨(dú)存在，需要附屬在父Window上，比如常用的Dialog。系統(tǒng)Window是需要聲明權(quán)限再創(chuàng)建的window，如toast等。
window有z-ordered屬性，層級越大，越在頂層。應(yīng)用window層級1-99，子window1000-1999，系統(tǒng)2000-2999。這此層級對應(yīng)著windowManager的type參數(shù)。系統(tǒng)層級常用的有兩個(gè)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(quán)限<uses-permission andorid:name="android.permission.SYSTEM_ALERT_WINDOW"/>。
有了對window的基本認(rèn)識之后，我們來看下它底層如何實(shí)現(xiàn)加載View的。
二、window的創(chuàng)建
其實(shí)Window的創(chuàng)建跟之前我寫的一篇博客LayoutInflater源碼分析有點(diǎn)相似。Window的創(chuàng)建是在Activity創(chuàng)建的attach方法中，通過PolicyManager的makeNewWindow方法。Activity中實(shí)現(xiàn)了Window的Callback接口，因此當(dāng)window狀態(tài)改變時(shí)就會回調(diào)Activity方法。如onAttachedToWindow等。PolicyManager的真正實(shí)現(xiàn)類是Policy，看下它的代碼：
public Window makeNewWindow(Context context) { return new PhoneWindow(context); } 到此Window創(chuàng)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(shè)置內(nèi)容和設(shè)置ActionBar。window的具體實(shí)現(xiàn)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(zhí)行：
1.如果沒有DecorView，在installDecor中的generateDecor()創(chuàng)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(diào)Activity的onContentChanged接口。
經(jīng)過以上操作，DecorView創(chuàng)建了，但還沒有正式添加到Window中。在ActivityResumeActivity中首先會調(diào)用Activity的onResume，再調(diào)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(nèi)部機(jī)制
1.window的添加
一個(gè)window對應(yīng)一個(gè)view和一個(gè)viewRootImpl,window和view通過ViewRootImpl來建立聯(lián)系，它并不存在，實(shí)體是view。只能通過 windowManager來操作它。
windowManager的實(shí)現(xiàn)類是windowManagerImpl。它并沒有直接實(shí)現(xiàn)三大操作，而是委托給WindowManagerGlobal。addView的實(shí)現(xiàn)分為以下幾步：
1）.檢查參數(shù)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(chuàng)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(gè)Binder對象，真正的實(shí)現(xiàn)類是 Session，window的添加是一次IPC調(diào)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(nèi)部會通過WindowManagerService來實(shí)現(xiàn)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(nèi)部會為每一個(gè)應(yīng)用保留一個(gè)單獨(dú)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(diào)用findViewLocked來查找刪除view的索引，這個(gè)過程就是建立數(shù)組遍歷。然后再調(diào)用removeViewLocked來做進(jìn)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(diào)用doDie，如果是removeView，用handler發(fā)送消息，ViewRootImpl中的Handler會處理消息并調(diào)用doDie。重點(diǎn)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(guān)工作，比如清數(shù)據(jù)，回調(diào)等。
2.通過Session的remove方法刪除Window,最終調(diào)用WindowManagerService的removeWindow
3.調(diào)用dispathDetachedFromWindow，在內(nèi)部會調(diào)用onDetachedFromWindow()和onDetachedFromWindowInternal()。當(dāng)view移除時(shí)會調(diào)用onDetachedFromWindow，它用于作一些資源回收。
4.通過doRemoveView刷新數(shù)據(jù)，刪除相關(guān)數(shù)據(jù)，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(gè)過程由WindowManagerService實(shí)現(xiàn)。這跟上面類似，就不再重復(fù)，到此Window底層源碼就分析完啦。
以上就是本文的全部內(nèi)容,希望對大家的學(xué)習(xí)有所幫助。
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