Android中Window添加View的底层原理
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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);
public void setContentView(int layoutResID)
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
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();
void makeVisible()
if (!mWindowAdded)
ViewManager wm = getWindowManager();
wm.addView(mDecor, getWindow().getAttributes());
mWindowAdded = true;
mDecor.setVisibility(View.VISIBLE);
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);root.setView(view, wparams, panelParentView); public void requestLayout()
if (!mHandlingLayoutInLayoutRequest)
checkThread();
mLayoutRequested = true;
scheduleTraversals();
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);
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);
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);
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;
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);
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);
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