Android中Window添加View的底层原理

2020-01-02 07:02:21

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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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