View绘制作业流程专业资料

//final办法，子类不可重写publicfinalvoidmeasure(intwidthMeasureSpec，intheightMeasureSpec){......//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protectedvoidonMeasure(intwidthMeasureSpec，intheightMeasureSpec){View绘制流程第一步：递归measure源码分析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。publicstaticintgetDefaultSize(intsize，intmeasureSpec){intresult=size;//通过MeasureSpec解析获取mode与sizeintspecMode=MeasureSpec.getMode(measureSpec);intspecSize=MeasureSpec.getSize(measureSpec);switch(specMode){caseMeasureSpec.UNSPECIFIED:result=size;break;caseMeasureSpec.AT_MOST:caseMeasureSpec.EXACTLY:result=specSize;break;}returnresult;}protectedintgetSuggestedMinimumWidth(){return(mBackground==null)?mMinWidth：max(mMinWidth，mBackground.getMinimumWidth());}protectedintgetSuggestedMinimumHeight(){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。protectedvoidmeasureChildWithMargins(Viewchild,intparentWidthMeasureSpe，cintwidthUsed,intparentHeightMeasureSpe，cintheightUsed){//获取子视图LayoutParamsfinalMarginLayoutParamslp=(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finalintchildWidthMeasureSpec=getChildMeasureSpec(parentWidthMeasureSpec,mPaddingLeft+mPaddingRight+lp.leftMargin+lp.rightMargin+widthUsed，lp.width);finalintchildHeightMeasureSpec=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。publicstaticintgetChildMeasureSpec(intspec，intpadding，intchildDimension){//获取当前ParentViewMode和SizeintspecMode=MeasureSpec.getMode(spec);intspecSize=MeasureSpec.getSize(spec);//获取Parentsize与padding差值（也就是Parent剩余大小），若差值不大于0直接返回0intsize=Math.max(0，specSize-padding);//定义返回值存储变量intresultSize=0;intresultMode=0;//根据当前ParentMode进行switch分支逻辑switch(specMode){//Parenthasimposedanexactsizeonus//默认RootViewMode就是EXACTLYcaseMeasureSpec.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EXACTLYresultSize=childDimension;resultMode=MeasureSpec.EXACTLY;}elseif(childDimension==LayoutParams.MATCH_PARENT){/如/果childlayout_wOrh属性在xml或者java中予以//MATCH_PARENT//Childwantstobeoursize.Sobeit./设/立childsize为size，mode为EXACTLYresultSize=size;resultMode=MeasureSpec.EXACTLY;}elseif(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//Childwantstodetermineitsownsize.Itcan'tbe//biggerthanus.resultSize=size;resultMode=MeasureSpec.AT_MOST;}break;......View绘制流程第二步：递归layout源码分析//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returnMeasureSpec.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；ViewGrouplayout办法，如下：@Overridepublicfinalvoidlayout(intl，intt，intr，intb){......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：publicvoidlayout(intl，intt，intr，intb){//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//layoutbooleanchanged=isLayoutModeOptical(mParent)?setOpticalFrame(，lt，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：@OverrideprotectedabstractvoidonLayout(booleanchanged,intl，intt，intr，intb);关于getWidth()、getHeight()和getMeasuredWidth()、getMeasuredHeight()这两对办法之间区别publicfinalintgetMeasuredWidth(){returnmMeasuredWidth&MEASURED_SIZE_MASK;}publicfinalintgetMeasuredHeight(){returnmMeasuredHeight&MEASURED_SIZE_MASK;}publicfinalintgetWidth(){returnmRight-mLeft;View绘制流程第三步：递归draw源码分析}publicfinalintgetHeight(){returnmBottom-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ViewGroup没有重写Viewdraw办法，因此如下直接从Viewdraw办法开始publicvoiddraw(Canvascanvas){//Step1，drawthebackground，ifneededif(!dirtyOpaque){drawBackground(canvas);}//skipstep2&5ifpossible(commoncase)//Step2，savethecanvas'layersif(drawTop){canvas.saveLayer(l