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首页 > 软件编程 > Android > Android中Window添加View的底层原理

Android中Window添加View的底层原理

作者:showCar

这篇文章主要介绍了Android中Window添加View的底层原理,需要的朋友可以参考下

一、WIndow和windowManager
Window是一个抽象类,它的具体实现是PhoneWindow,创建一个window很简单,只需要创建一个windowManager即可,window具体实现在windowManagerService中,windowManager和windowManagerService的交互是一个IPC的过程。
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两个属性很重要,下面对一些属性进行介绍,首先是flags:
FLAG_NOT_TOUCH_MODAL表示不需要获取焦点,也不需要接收各种输入,最终事件直接传递给下层具有焦点的window。
FLAG_NOT_FOCUSABLE:在此window外的区域单击事件传递到底层window中。当前的区域则自己处理,这个一般都要设置,很重要。
FLAG_SHOW_WHEN_LOCKED :开启可以让window显示在锁屏界面上。
再来看下type这个参数:
window有三种类型:应用window,子window,系统window。应用类对应一个Activity,子Window不能单独存在,需要附属在父Window上,比如常用的Dialog。系统Window是需要声明权限再创建的window,如toast等。
window有z-ordered属性,层级越大,越在顶层。应用window层级1-99,子window1000-1999,系统2000-2999。这此层级对应着windowManager的type参数。系统层级常用的有两个TYPE_SYSTEM_OVERLAY或者TYPE_SYSTEM_ERROR。比如想用TYPE_SYSTEM_ERROR,只需
mLayoutParams.type = LayoutParams.TYPE_SYSTEM_ERROR。还要添加权限<uses-permission andorid:name="android.permission.SYSTEM_ALERT_WINDOW"/>。
有了对window的基本认识之后,我们来看下它底层如何实现加载View的。
二、window的创建
其实Window的创建跟之前我写的一篇博客LayoutInflater源码分析有点相似。Window的创建是在Activity创建的attach方法中,通过PolicyManager的makeNewWindow方法。Activity中实现了Window的Callback接口,因此当window状态改变时就会回调Activity方法。如onAttachedToWindow等。PolicyManager的真正实现类是Policy,看下它的代码:

public Window makeNewWindow(Context context) { 
    return new PhoneWindow(context); 
  } 

到此Window创建完成。
下面分析view是如何附属到window上的。看Activity的setContentView方法。

public void setContentView(int layoutResID) { 
    getWindow().setContentView(layoutResID); 
    initWindowDecorActionBar(); 
  } 

两部分,设置内容和设置ActionBar。window的具体实现是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。
这里分三步执行:
1.如果没有DecorView,在installDecor中的generateDecor()创建DecorView。之前就分析过,这次就不再分析它了。
2.将View添加到decorview中的mContentParent中。
3.回调Activity的onContentChanged接口。
经过以上操作,DecorView创建了,但还没有正式添加到Window中。在ActivityResumeActivity中首先会调用Activity的onResume,再调用Activity的makeVisible,makeVisible中真正添加view ,代码如下:

void makeVisible() { 
   if (!mWindowAdded) { 
     ViewManager wm = getWindowManager(); 
     wm.addView(mDecor, getWindow().getAttributes()); 
     mWindowAdded = true; 
   } 
   mDecor.setVisibility(View.VISIBLE); 
 } 

通过上面的addView方法将View添加到Window。
三、Window操作View内部机制
1.window的添加
一个window对应一个view和一个viewRootImpl,window和view通过ViewRootImpl来建立联系,它并不存在,实体是view。只能通过 windowManager来操作它。
windowManager的实现类是windowManagerImpl。它并没有直接实现三大操作,而是委托给WindowManagerGlobal。addView的实现分为以下几步:
1).检查参数是否合法。

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).创建ViewRootImpl并将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).通过ViewRootImpl来更新界面并完成window的添加过程 。
root.setView(view, wparams, panelParentView); 
上面的root就是ViewRootImpl,setView中通过requestLayout()来完成异步刷新,看下requestLayout:

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

接下来通过WindowSession来完成window添加过程,WindowSession是一个Binder对象,真正的实现类是 Session,window的添加是一次IPC调用。

 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内部会通过WindowManagerService来实现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内部会为每一个应用保留一个单独的session。
2.window的删除
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); 
    } 
  } 

首先调用findViewLocked来查找删除view的索引,这个过程就是建立数组遍历。然后再调用removeViewLocked来做进一步的删除。

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); 
      } 
    } 
  } 

真正删除操作是viewRootImpl来完成的。windowManager提供了两种删除接口,removeViewImmediate,removeView。它们分别表示异步删除和同步删除。具体的删除操作由ViewRootImpl的die来完成。

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,立即调用doDie,如果是removeView,用handler发送消息,ViewRootImpl中的Handler会处理消息并调用doDie。重点看下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.垃圾回收相关工作,比如清数据,回调等。
2.通过Session的remove方法删除Window,最终调用WindowManagerService的removeWindow

3.调用dispathDetachedFromWindow,在内部会调用onDetachedFromWindow()和onDetachedFromWindowInternal()。当view移除时会调用onDetachedFromWindow,它用于作一些资源回收。
4.通过doRemoveView刷新数据,删除相关数据,如在mRoot,mDyingViews中删除对象等。

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); 
    } 
  } 

通过viewRootImpl的setLayoutParams更新viewRootImpl的layoutParams,接着scheduleTraversals对view重新布局,包括测量,布局,重绘,此外它还会通过WindowSession来更新window。这个过程由WindowManagerService实现。这跟上面类似,就不再重复,到此Window底层源码就分析完啦。

以上就是本文的全部内容,希望对大家的学习有所帮助。

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