Android中Window添加View的底層原理

更新時間：2016年03月03日 10:54:17 作者：showCar

這篇文章主要介紹了Android中Window添加View的底層原理,需要的朋友可以參考下

一、WIndow和windowManager
Window是一個抽象類，它的具體實現(xiàn)是PhoneWindow，創(chuàng)建一個window很簡單，只需要創(chuàng)建一個windowManager即可，window具體實現(xiàn)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(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(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的基本認識之后，我們來看下它底層如何實現(xiàn)加載View的。
二、window的創(chuàng)建
其實Window的創(chuàng)建跟之前我寫的一篇博客LayoutInflater源碼分析有點相似。Window的創(chuàng)建是在Activity創(chuàng)建的attach方法中，通過PolicyManager的makeNewWindow方法。Activity中實現(xiàn)了Window的Callback接口，因此當(dāng)window狀態(tài)改變時就會回調(diào)Activity方法。如onAttachedToWindow等。PolicyManager的真正實現(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?？碅ctivity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)部機制
1.window的添加
一個window對應(yīng)一個view和一個viewRootImpl,window和view通過ViewRootImpl來建立聯(lián)系，它并不存在，實體是view。只能通過 windowManager來操作它。
windowManager的實現(xiàn)類是windowManagerImpl。它并沒有直接實現(xiàn)三大操作，而是委托給WindowManagerGlobal。addView的實現(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Binder對象，真正的實現(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)部會為每一個應(yīng)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(diào)用findViewLocked來查找刪除view的索引，這個過程就是建立數(shù)組遍歷。然后再調(diào)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(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。這個過程由WindowManagerService實現(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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