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 Android教程網 >> Android技術 >> 關於Android編程 >> Android中Window添加View的底層原理

Android中Window添加View的底層原理

編輯:關於Android編程

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<uses-permission andorid:name="android.permission.SYSTEM_ALERT_WINDOW"/>。
有了對window的基本認識之後,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。
這裡分三步執行:
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,它並不存在,實體是view。只能通過 windowManager來操作它。
windowManager的實現類是windowManagerImpl。它並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並將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來更新界面並完成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。然後再調用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會處理消息並調用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,它用於作一些資源回收。
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。

以上就是本文的全部內容,希望對大家的學習有所幫助。

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