View绘制作业流程专业资料.doc

View绘制流程第一步：递归measure源码分析/final办法，子类不可重写public final void measure(int widthMeasureSpec，int heightMeasureSpec) ./回调onMeasure()办法onMeasure(widthMeasureSpec，heightMeasureSpec);这个办法两个参数都是父View传递过来，代表了父view规格。她由两某些构成，高2位表达MODE，低30位表达size。/ViewonMeasure默认实现办法protected void onMeasure(int widthMeasureSpec，int heightMeasureSpec) setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth()，widthMeasureSpec),getDefaultSize(getSuggestedMinimumHeight()，heightMeasureSpec);对于非ViewGroupView而言，通过调用上面默认onMeasure即可完毕View测量。setMeasuredDimension函数是一种很核心函数，它完毕了对View成员变量mMeasuredWidth和mMeasuredHeight变量赋值。public static int getDefaultSize(int size，int measureSpec) int result = size;/通过MeasureSpec解析获取mode与sizeint specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec);switch (specMode) case MeasureSpec.UNSPECIFIED: result = size; break; case MeasureSpec.AT_MOST: case MeasureSpec.EXACTLY: result = specSize; break; return result;protected int getSuggestedMinimumWidth() return (mBackground = null) ?mMinWidth ：max(mMinWidth，mBackground.getMinimumWidth();protected int getSuggestedMinimumHeight() return (mBackground = null) ?mMinHeight ：max(mMinHeight，mBackground.getMinimumHeight();在ViewGroup中定义了measureChildren，measureChild，measureChildWith-Margins办法来对子视图进行测量，measureChildren内部实质只是循环调用measureChild。protected void measureChildWithMargins(View child, int parentWidthMeasureSpec，int widthUsed, int parentHeightMeasureSpec，int heightUsed) /获取子视图LayoutParamsfinal MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();/调节MeasureSpec/通过这两个参数以及子视图自身LayoutParams来共同决定子视图测量规格final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin + widthUsed，lp.width);final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec, mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin + heightUsed，lp.height);/调运子Viewmeasure办法，子Viewmeasure中会回调子View/onMeasure办法child.measure(childWidthMeasureSpec，childHeightMeasureSpec);该办法就是对父视图提供measureSpec参数结合自身LayoutParams参数进行了调节，然后再来调用child.measure()办法，详细通过办法getChildMeasureSpec来进行参数调节。public static int getChildMeasureSpec(int spec，int padding，int childDimension) /获取当前Parent ViewMode和Size int specMode = MeasureSpec.getMode(spec); int specSize = MeasureSpec.getSize(spec); /获取Parent size与padding差值（也就是Parent剩余大小），若差值不大于0直接返回0 int size = Math.max(0，specSize - padding); /定义返回值存储变量 int resultSize = 0; int resultMode = 0; /根据当前ParentMode进行switch分支逻辑 switch (specMode) / Parent has imposed an exact size on us /默认Root ViewMode就是EXACTLY case MeasureSpec.EXACTLY: if (childDimension = 0) /如果childlayout_wOrh属性在xml或者java中予以详细大/于等于0数值 /设立childsize为真实layout_wOrh属性值，mode为EXACTLY resultSize = childDimension; resultMode = MeasureSpec.EXACTLY; else if (childDimension = LayoutParams.MATCH_PARENT) /如果childlayout_wOrh属性在xml或者java中予以/MATCH_PARENT / Child wants to be our size. So be it. /设立childsize为size，mode为EXACTLY resultSize = size; resultMode = MeasureSpec.EXACTLY; else if (childDimension = LayoutParams.WRAP_CONTENT) /如果childlayout_wOrh属性在xml或者java中予以/WRAP_CONTENT /设立childsize为size，mode为AT_MOST / Child wants to determine its own size. It cant be / bigger than us. resultSize = size; resultMode = MeasureSpec.AT_MOST; break; . /其她Mode分支类似 /将mode与size通过MeasureSpec办法整合为32位整数返回 return MeasureSpec.makeMeasureSpec(resultSize，resultMode);用ViewgetMeasuredWidth()和getMeasuredHeight()办法来获取View测量宽高，必要保证这两个办法在onMeasure流程之后被调用才干返回有效值。MeasureSpec（View内部类）测量规格为int型，值由高2位规格模式specMode和低30位详细尺寸specSize构成。其中specMode只有三种值：MeasureSpec.EXACTLY /拟定模式，父View但愿子View大小是拟定，由specSize决定；MeasureSpec.AT_MOST /最多模式，父View但愿子View大小最多是specSize指定值；MeasureSpec.UNSPECIFIED /未指定模式，父View完全根据子View设计值来决定；View绘制流程第二步：递归layout源码分析ViewGrouplayout办法，如下：Overridepublic final void layout(int l，int t，int r，int b) . super.layout(l，t，r，b);.调运了View父类layout办法，因此咱们看下Viewlayout源码，如下：public void layout(int l，int t，int r，int b) /实质都是调用setFrame办法把参数分别赋值给mLeft、mTop、mRight和/mBottom这几种变量/判断View位置与否发生过变化，以拟定有无必要对当前View进行重新/layout 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);/ViewGrouponLayout办法，如下：Overrideprotected abstract void onLayout(boolean changed,int l，int t，int r，int b);关于getWidth()、getHeight()和getMeasuredWidth()、getMeasuredHeight()这两对办法之间区别public final int getMeasuredWidth () return mMeasuredWidth & MEASURED_SIZE_MASK;public final int getMeasuredHeight() return mMeasuredHeight & MEASURED_SIZE_MASK;public final int getWidth() return mRight - mLeft;public final int getHeight() return mBottom - mTop;View.layout办法可被重载，ViewGroup.layout为final不可重载，ViewGroup.onLayout为abstract，子类必要重载实现自己位置逻辑。凡是layout_XXX布局属性基本都针对是包括子ViewViewGroup，当对一种没有父容器View设立有关layout_XXX属性是没有任何意义使用ViewgetWidth()和getHeight()办法来获取View测量宽高，必要保证这两个办法在onLayout流程之后被调用才干返回有效值View绘制流程第三步：递归draw源码分析ViewGroup没有重写Viewdraw办法，因此如下直接从Viewdraw办法开始public void draw(Canvas canvas) / Step 1，draw the background，if needed if (!dirtyOpaque) drawBackground(canvas); / skip step 2 & 5 if possible (common case) / Step 2，save the canvas layers if (drawTop) canvas.saveLayer(left，top，right，top + length，null，flags); / Step 3，draw the content if (!dirtyOpaque) onDraw(canvas); / Step 4，draw the children dispatchDraw(canvas); / Step 5，draw the fade effect and restore layers if (drawTop) matrix.setScale(1，fadeHeight * topFadeStrength); matrix.postTranslate(left，top); fade.setLocalMatrix(matrix); p.setShader(fade); canvas.drawRect(left，top，right，top + length，p); / Step 6，draw decorations (scrollbars) onDrawScrollBars(canvas);private void drawBackground(Canvas canvas) /获取xml中通过android:background属性或者代码中/setBackgroundColor()、setBackgroundResource()等办法进行赋值背景/Drawable final Drawable background = mBackground; . /依照layout过程拟定View位置来设立背景绘制区域 if (mBackgroundSizeChanged) background.setBounds(0，0，mRight - mLeft，mBottom - mTop); mBackgroundSizeChanged = false; rebuildOutline(); . /调用Drawabledraw()办法来完毕背景绘制工作 background.draw(canvas); ./ViewonDraw办法，这是一种空办法。由于每个View内容某些是各不相似，/因此需要由子类去实现详细逻辑。protected void onDraw(Canvas canvas) / ViewdispatchDraw()办法是一种空办法，如果View包括子类需要重写她，所/以咱们有必要看下ViewGroupdispatchDraw办法源码Overrideprotected void dispatchDraw(Canvas canvas) .final int childrenCount = mChildrenCount; final View children = mChildren; for (int i = 0；i = 0；i-) more |= drawChild(canvas，child，drawingTime); / ViewGroup的确重写了ViewdispatchDraw()办法，该办法内部会遍历每个子/View，然后调用drawChild()办法，咱们可以看下ViewGroupdrawChild办法protected boolean drawChild(Canvas canvas，View child，long drawingTime) return child.draw(canvas，this，drawingTime);drawChild()办法调运了子Viewdraw()办法。因此说ViewGroup类已经为咱们重写了dispatchDraw()功能实现，咱们普通不需要重写该办法，但可以重载父类函数实现详细功能。在获取画布剪切区时会自动解决掉padding，子View获取Canvas不用关注这些逻辑，只用关怀如何绘制即可。默认状况下子ViewViewGroup.drawChild绘制顺序和子View被添加顺序一致，但是你也可以重载ViewGroup.getChildDrawingOrder()办法提供不同顺序。Viewinvalidate办法源码分析View类中某些invalidate办法/This must be called from a UI thread. To call from a non-UI thread，/ call postInvalidate()public void invalidate(Rect dirty) final int scrollX = mScrollX; final int scrollY = mScrollY; /实质还是调运invalidateInternal办法 invalidateInternal(dirty.left - scrollX，dirty.top - scrollY, dirty.right - scrollX，dirty.bottom - scrollY，true，false);/This must be called from a UI thread. To call from a non-UI thread，/ call postInvalidate()public void invalidate(int l，int t，int r，int b) final int scrollX = mScrollX; final int scrollY = mScrollY; /实质还是调运invalidateInternal办法 invalidateInternal(l - scrollX，t - scrollY，r - scrollX，b - scrollY，true，false);/This must be called from a UI thread. To call from a non-UI thread，/ call postInvalidate()public void invalidate() /invalidate实质还是调运invalidateInternal办法 invalidate(true); /this function can be called with invalidateCache set to false to /skip that invalidation step void invalidate(boolean invalidateCache) /实质还是调运invalidateInternal办法invalidateInternal(0，0，mRight - mLeft，mBottom - mTop，invalidateCache，true);/所有invalidate最后调运办法void invalidateInternal(int l，int t，int r，int b，boolean invalidateCache，boolean fullInvalidate) . / Propagate the damage rectangle to the parent view. final AttachInfo ai = mAttachInfo; final ViewParent p = mParent; if (p != null & ai != null & l r & t b) final Rect damage = ai.mTmpInvalRect; /设立刷新区域 damage.set(l，t，r，b); /传递调运Parent ViewGroupinvalidateChild办法 p.invalidateChild(this，damage); .Viewinvalidate（invalidateInternal）办法实质是将要刷新区域直接传递给了父ViewGroupinvalidateChild办法，在invalidate中，调用父ViewinvalidateChild，这是一种从当前向上级父View回溯过程ViewGroupinvalidateChild办法public final void invalidateChild(View child，final Rect dirty) ViewParent parent = this; final AttachInfo attachInfo = mAttachInfo; . do /循环层层上级调运，直到ViewRootImpl会返回null parent = parent.invalidateChildInParent(location，dirty); while (parent != null);最后传递到ViewRootImplinvalidateChildInParent办法结束，因此咱们看下ViewRootImplinvalidateChildInParent办法Overridepublic ViewParent invalidateChildInParent(int location，Rect dirty) . /View调运invalidate最后层层上传到ViewRootImpl后最后触发了该办法 scheduleTraversals(); . return null;这个ViewRootImpl类invalidateChildInParent办法直接返回了null，结束了那个do while循环。scheduleTraversals会通过HandlerRunnable发送一种异步消息，调运doTraversal办法，然后最后调用performTraversals()执行重绘。因此说View调运invalidate办法实质是层层上传到父级，直到传递到ViewRootImpl后触发了scheduleTraversals办法，然后整个View树开始重新按照上面分析View绘制流程进行重绘任务。ViewpostInvalidate办法源码分析invalidate办法只能在UI Thread中执行，其她线程中需要使用postInvalidate办法public void postInvalidate() postInvalidateDelayed(0);public void postInvalidateDelayed(long delayMilliseconds) final AttachInfo attachInfo = mAttachInfo; /核心，实质就是调运了ViewRootImpl.dispatchInvalidateDelayed办法 if (attachInfo != null) attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this，delayMilliseconds); public void dispatchInvalidateDelayed(View view，long delayMilliseconds) Message msg = mHandler.obtainMessage(MSG_INVALIDATE，view); mHandler.sendMessageDelayed(msg，delayMilliseconds);调运ViewRootImpl类dispatchInvalidateDelayed办法，通过ViewRootImpl类Handler发送了一条MSG_INVALIDATE消息，继续追踪这条消息解决可以发现：public void handleMessage(Message msg) . switch (msg.what) case MSG_INVALIDATE: (View)msg.obj).invalidate(); break; . .invalidate系列办法祈求重绘View树（也就是draw办法），如果View大小没有发生变化就不会调用layout过程，并且只绘制那些“需要重绘”View，也就是哪个View(View只绘制该View，ViewGroup绘制整个ViewGroup)祈求invalidate系列办法，就绘制该View。setContentView办法源码分析Overridepublic void setContentView(View view，ViewGroup.LayoutParams params) ./如果mContentParent为空进行某些初始化 if (mContentParent = null) installDecor(); . /把咱们view追加到mContentParent mContentParent.addView(view，params); .public void addView(View child) addView(child，-1);public void addView(View child，int index) . addView(child，index，params); public void addView(View child，int index，LayoutParams params) .requestLayout();invalidate(true);通过setContentView办法将咱们要展示界面传入该办法，该办法会将咱们界面通过addView追加到id为content一种FrameLayout中，然后addView办法中通过调运invalidate(true)去告知触发ViewRootImpl类performTraversals()办法，至此递归绘制咱们自定义所有布局。ViewrequestLayout办法源码分析public void requestLayout() . if (mParent != null & !mParent.isLayoutRequested() /由此向ViewParent祈求布局 /从这个View开始向上始终requestLayout，最后到达ViewRootImpl/requestLayout mParent.requestLayout(); .Overridepublic void requestLayout() if (!mHandlingLayoutInLayoutRequest) checkThread(); mLayoutRequested = true; /View调运requestLayout最后层层上传到ViewRootImpl后最后触发了/该办法 scheduleTraversals(); requestLayout()办法会调用measure过程和layout过程，不会调用draw过程，也不会重新绘制任何View涉及该调用者自身。