创建Window
在Activity的attach方法中通过调用PolicyManager.makeNewWindo创建Window,将一个View add到WindowManager时,WindowManagerImpl创建一个ViewRoot来管理该窗口的根View。并通过ViewRoot.setView方法把该View传给ViewRoot。
final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token, int ident, Application application, Intent intent, ActivityInfo info, CharSequence title, Activity parent, String id, NonConfigurationInstances lastNonConfigurationInstances, Configuration config) { attachBaseContext(context); mFragments.attachActivity(this, mContainer, null); mWindow = PolicyManager.makeNewWindow(this); mWindow.setCallback(this); mWindow.getLayoutInflater().setPrivateFactory(this);
创建DecorView
DecorView为整个Window界面的最顶层View。
Activity中的Window对象帮我们创建了一个PhoneWindow内部类DecorView(父类为FrameLayout)窗口顶层视图,然后通过LayoutInflater将xml内容布局解析成View树形结构添加到DecorView顶层视图中id为content的FrameLayout父容器上面。Activity的content内容布局最终会添加到DecorView窗口顶层视图上面。
protected boolean initializePanelDecor(PanelFeatureState st) { st.decorView = new DecorView(getContext(), st.featureId); st.gravity = Gravity.CENTER | Gravity.BOTTOM; st.setStyle(getContext()); return true; }
创建ViewRoot并关联View
WindowManagerImpl保存DecorView到mViews,创建对应的ViewRoot;
ViewRoot用于管理窗口的根View,并和global window manger进行交互。ViewRoot中有一个nested class: W,W是一个Binder子类,用于接收global window manager的各种消息, 如按键消息, 触摸消息等。 ViewRoot有一个W类型的成员mWindow,ViewRoot在Constructor中创建一个W的instance并赋值给mWindow。 ViewRoot是Handler的子类, W会通过Looper把消息传递给ViewRoot。 ViewRoot在setView方法中把mWindow传给sWindowSession。
public void addView(View view, ViewGroup.LayoutParams params, Display display, Window parentWindow) { 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); } ViewRootImpl root; View panelParentView = null; synchronized (mLock) { // Start watching for system property changes. if (mSystemPropertyUpdater == null) { mSystemPropertyUpdater = new Runnable() { @Override public void run() { synchronized (mLock) { for (ViewRootImpl viewRoot : mRoots) { viewRoot.loadSystemProperties(); } } } }; SystemProperties.addChangeCallback(mSystemPropertyUpdater); } int index = findViewLocked(view, false); if (index >= 0) { throw new IllegalStateException("View " + view + " has already been added to the window manager."); } // If this is a panel window, then find the window it is being // attached to for future reference. if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW && wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) { final int count = mViews != null ? mViews.length : 0; for (int i=0; i<count; i++) { if (mRoots[i].mWindow.asBinder() == wparams.token) { panelParentView = mViews[i]; } } } root = new ViewRootImpl(view.getContext(), display); view.setLayoutParams(wparams); if (mViews == null) { index = 1; mViews = new View[1]; mRoots = new ViewRootImpl[1]; mParams = new WindowManager.LayoutParams[1]; } else { index = mViews.length + 1; Object[] old = mViews; mViews = new View[index]; System.arraycopy(old, 0, mViews, 0, index-1); old = mRoots; mRoots = new ViewRootImpl[index]; System.arraycopy(old, 0, mRoots, 0, index-1); old = mParams; mParams = new WindowManager.LayoutParams[index]; System.arraycopy(old, 0, mParams, 0, index-1); } index--; mViews[index] = view; mRoots[index] = root; mParams[index] = wparams; } // do this last because it fires off messages to start doing things try { root.setView(view, wparams, panelParentView); } catch (RuntimeException e) { // BadTokenException or InvalidDisplayException, clean up. synchronized (mLock) { final int index = findViewLocked(view, false); if (index >= 0) { removeViewLocked(index, true); } } throw e; } }
ViewRoot是GUI管理系统与GUI呈现系统之间的桥梁,需要注意它并不是一个View类型。
它的主要作用如下:
1、向DecorView分发收到的用户发起的event事件,如按键,触屏,轨迹球等事件;
2、与WindowManagerService交互,完成整个Activity的GUI的绘制。
View绘制基本流程
这里先给出Android系统View的绘制流程:依次执行View类里面的如下三个方法:
measure(int ,int) :测量View的大小
layout(int ,int ,int ,int) :设置子View的位置
draw(Canvas) :绘制View内容到Canvas画布上
整个View树的绘图流程是在ViewRoot.Java类的performTraversals()函数展开的,该函数做的执行过程可简单概况为根据之前设置的状态,判断是否需要重新计算视图大小(measure)、是否重新需要安置视图的位置(layout)、以及是否需要重绘 (draw)
mesarue()测量过程
主要作用:为整个View树计算实际的大小,即设置实际的高(mMeasuredHeight)和宽(mMeasureWidth),每个View的控件的实际宽高都是由父视图和本身视图决定的。
具体的调用如下:
ViewRootImpl 的performTraversals方法中,调用measureHierarchy,然后调用performMeasure
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) { Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure"); try { mView.measure(childWidthMeasureSpec, childHeightMeasureSpec); } finally { Trace.traceEnd(Trace.TRACE_TAG_VIEW); } }
ViewRoot根对象地属性mView(其类型一般为ViewGroup类型)调用measure()方法去计算View树的大小,回调View/ViewGroup对象的onMeasure()方法,该方法实现的功能如下:
1、设置本View视图的最终大小,该功能的实现通过调用setMeasuredDimension()方法去设置实际的高(mMeasuredHeight)和宽(mMeasureWidth)
2、如果该View对象是个ViewGroup类型,需要重写onMeasure()方法,对其子视图进行遍历的measure()过程。
对每个子视图的measure()过程,是通过调用父类ViewGroup.java类里的measureChildWithMargins()方法去实现,该方法内部只是简单地调用了View对象的measure()方法。
整个measure调用流程就是个树形的递归过程measure()方法两个参数都是父View传递过来的,也就是代表了父view的规格。他由两部分组成,高2位表示MODE,定义在MeasureSpec类(View的内部类)中,有三种类型,MeasureSpec.EXACTLY表示确定大小, MeasureSpec.AT_MOST表示最大大小, MeasureSpec.UNSPECIFIED不确定。低30位表示size,也就是父View的大小。对于系统Window类的DecorVIew对象Mode一般都为MeasureSpec.EXACTLY ,而size分别对应屏幕宽高。对于子View来说大小是由父View和子View共同决定的。
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec), getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec)); }
protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) { boolean optical = isLayoutModeOptical(this); if (optical != isLayoutModeOptical(mParent)) { Insets insets = getOpticalInsets(); int opticalWidth = insets.left + insets.right; int opticalHeight = insets.top + insets.bottom; measuredWidth += optical ? opticalWidth : -opticalWidth; measuredHeight += optical ? opticalHeight : -opticalHeight; } mMeasuredWidth = measuredWidth; mMeasuredHeight = measuredHeight; mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET; }
layout布局过程
主要作用 :为将整个根据子视图的大小以及布局参数将View树放到合适的位置上。
具体的调用如下:
ViewRootImpl 的performTraversals方法中,调用performLayout
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth, int desiredWindowHeight) { mLayoutRequested = false; mScrollMayChange = true; mInLayout = true; final View host = mView; if (DEBUG_ORIENTATION || DEBUG_LAYOUT) { Log.v(TAG, "Laying out " + host + " to (" + host.getMeasuredWidth() + ", " + host.getMeasuredHeight() + ")"); } Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout"); try { host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()); mInLayout = false; int numViewsRequestingLayout = mLayoutRequesters.size(); if (numViewsRequestingLayout > 0) { // requestLayout() was called during layout. // If no layout-request flags are set on the requesting views, there is no problem. // If some requests are still pending, then we need to clear those flags and do // a full request/measure/layout pass to handle this situation. ArrayList<View> validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, false); if (validLayoutRequesters != null) { // Set this flag to indicate that any further requests are happening during // the second pass, which may result in posting those requests to the next // frame instead mHandlingLayoutInLayoutRequest = true; // Process fresh layout requests, then measure and layout int numValidRequests = validLayoutRequesters.size(); for (int i = 0; i < numValidRequests; ++i) { final View view = validLayoutRequesters.get(i); Log.w("View", "requestLayout() improperly called by " + view + " during layout: running second layout pass"); view.requestLayout(); } measureHierarchy(host, lp, mView.getContext().getResources(), desiredWindowWidth, desiredWindowHeight); mInLayout = true; host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()); mHandlingLayoutInLayoutRequest = false; // Check the valid requests again, this time without checking/clearing the // layout flags, since requests happening during the second pass get noop'd validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, true); if (validLayoutRequesters != null) { final ArrayList<View> finalRequesters = validLayoutRequesters; // Post second-pass requests to the next frame getRunQueue().post(new Runnable() { @Override public void run() { int numValidRequests = finalRequesters.size(); for (int i = 0; i < numValidRequests; ++i) { final View view = finalRequesters.get(i); Log.w("View", "requestLayout() improperly called by " + view + " during second layout pass: posting in next frame"); view.requestLayout(); } } }); } } } } finally { Trace.traceEnd(Trace.TRACE_TAG_VIEW); } mInLayout = false; }
host.layout()开始View树的布局,继而回调给View/ViewGroup类中的layout()方法。具体流程如下
1 、layout方法会设置该View视图位于父视图的坐标轴,即mLeft,mTop,mLeft,mBottom(调用setFrame()函数去实现),接下来回调onLayout()方法(如果该View是ViewGroup对象,需要实现该方法,对每个子视图进行布局)。
2、如果该View是个ViewGroup类型,需要遍历每个子视图chiildView,调用该子视图的layout()方法去设置它的坐标值。
protected void onLayout(boolean changed, int left, int top, int right, int bottom) { }
public void layout(int l, int t, int r, int b) { int oldL = mLeft; int oldT = mTop; int oldB = mBottom; int oldR = mRight; boolean changed = isLayoutModeOptical(mParent) ? setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b); if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) { onLayout(changed, l, t, r, b); mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED; ListenerInfo li = mListenerInfo; if (li != null && li.mOnLayoutChangeListeners != null) { ArrayList<OnLayoutChangeListener> listenersCopy = (ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone(); int numListeners = listenersCopy.size(); for (int i = 0; i < numListeners; ++i) { listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB); } } } mPrivateFlags &= ~PFLAG_FORCE_LAYOUT; }
draw()绘图过程
ViewRootImpl 的performTraversals方法中,调用了mView的draw方法
mView.draw()开始绘制,draw()方法实现的功能如下:
1 、绘制该View的背景
2 、为显示渐变框做一些准备操作
3、调用onDraw()方法绘制视图本身 (每个View都需要重载该方法,ViewGroup不需要实现该方法)
4、调用dispatchDraw ()方法绘制子视图(如果该View类型不为ViewGroup,即不包含子视图,不需要重载该方法)
值得说明的是,ViewGroup类已经为我们重写了dispatchDraw ()的功能实现,应用程序一般不需要重写该方法,但可以重载父类函数实现具体的功能。
dispatchDraw()方法内部会遍历每个子视图,调用drawChild()去重新回调每个子视图的draw()方法。
5、绘制滚动条
刷新视图
Android中实现view的更新有两个方法,一个是invalidate,另一个是postInvalidate,其中前者是在UI线程自身中使用,而后者在非UI线程中使用。
requestLayout()方法 :会导致调用measure()过程 和 layout()过程 。
说明:只是对View树重新布局layout过程包括measure()和layout()过程,不会调用draw()过程,但不会重新绘制
任何视图包括该调用者本身。
一般引起invalidate()操作的函数如下:
1、直接调用invalidate()方法,请求重新draw(),但只会绘制调用者本身。
2、setSelection()方法 :请求重新draw(),但只会绘制调用者本身。
3、setVisibility()方法 : 当View可视状态在INVISIBLE转换VISIBLE时,会间接调用invalidate()方法,继而绘制该View。
4 、setEnabled()方法 : 请求重新draw(),但不会重新绘制任何视图包括该调用者本身。
内容参考源码,借鉴了网上的一些分析。