Android中Window添加View的底层原理

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。