Android 自定义View及其在布局文件中的使用示例(三):结合Android 4.4.2_r1源码分析onMeasure过程

MODE_MASK为:11000000000000000000000000000000

<com.project.summary.customview.CustomView
android:id="@+id/customView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:colorValue="@color/textRed"
app:textSize="20sp"
app:textString="ThistheCustomView1!!!"/>

1/**
2*Determinesthewidthofthisview
3*
4*@parammeasureSpec
5*AmeasureSpecpackedintoanint
6*@returnThewidthoftheview,honoringconstraintsfrommeasureSpec
7*/
8privateintmeasureWidth(intmeasureSpec){
9intresult=0;
10intspecMode=MeasureSpec.getMode(measureSpec);
11intspecSize=MeasureSpec.getSize(measureSpec);
12
13if(specMode==MeasureSpec.EXACTLY){
14//Weweretoldhowbigtobe
15result=specSize;
16}else{
17//Measurethetext
18result=(int)mTextPaint.measureText(mText)+getPaddingLeft()
19+getPaddingRight();
20if(specMode==MeasureSpec.AT_MOST){
21//RespectAT_MOSTvalueifthatwaswhatiscalledforby
22//measureSpec
23result=Math.min(result,specSize);
24}
25}
26
27returnresult;
28}

Q01:
protectedvoidonMeasure(intwidthMeasureSpec,intheightMeasureSpec)是一个override的方法,它接收两个参数,通过字面意思,我们知道,这两个参数分别为宽度测量规格,高度测量规格,此时,我们会有一个疑问,这两个参数是从哪里来的?

Q02:
调试结果出来,此时传入的measureSpec的值是-2147483648,到了这里,我们又会产生一个疑问,为什么是它?为什么是这个值?

privatevoidperformTraversals()
{
.......................................
1122WindowManager.LayoutParamslp=mWindowAttributes;//详见分析PERFORMTRAVERSALS()点1

.........................................................
1155Rectframe=mWinFrame;//详见分析PERFORMTRAVERSALS()点2
.......................................................
1563if(mWidth!=frame.width()||mHeight!=frame.height()){
1564mWidth=frame.width();
1565mHeight=frame.height();
1566}
1567
.......................................................................
PERFORMTRAVERSALS()点3:
1634if(!mStopped){
1635booleanfocusChangedDueToTouchMode=ensureTouchModeLocally(
1636(relayoutResult&WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE)!=0);
1637if(focusChangedDueToTouchMode||mWidth!=host.getMeasuredWidth()
1638||mHeight!=host.getMeasuredHeight()||contentInsetsChanged){
1639intchildWidthMeasureSpec=getRootMeasureSpec(mWidth,lp.width);//详见getRootMeasureSpec()方法的分析
1640intchildHeightMeasureSpec=getRootMeasureSpec(mHeight,lp.height);
1641
1642if(DEBUG_LAYOUT)Log.v(TAG,"Ooops,somethingchanged!mWidth="
1643+mWidth+"measuredWidth="+host.getMeasuredWidth()
1644+"mHeight="+mHeight
1645+"measuredHeight="+host.getMeasuredHeight()
1646+"coveredInsetsChanged="+contentInsetsChanged);
1647
1648//Askhosthowbigitwantstobe
1649performMeasure(childWidthMeasureSpec,childHeightMeasureSpec);
}

WindowManager.LayoutParamslp=mWindowAttributes;

finalWindowManager.LayoutParamsmWindowAttributes=newWindowManager.LayoutParams();

publicLayoutParams(){
super(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT);
type=TYPE_APPLICATION;
format=PixelFormat.OPAQUE;
}

super(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT);

5829publicstaticclassLayoutParams{
5830/**
5831*SpecialvaluefortheheightorwidthrequestedbyaView.
5832*FILL_PARENTmeansthattheviewwantstobeasbigasitsparent,
5833*minustheparent'spadding,ifany.Thisvalueisdeprecated
5834*startinginAPILevel8andreplacedby{@link#MATCH_PARENT}.
5835*/
5836@SuppressWarnings({"UnusedDeclaration"})
5837@Deprecated
5838publicstaticfinalintFILL_PARENT=-1;

..........................................

5918publicLayoutParams(intwidth,intheight){
5919this.width=width;
5920this.height=height;
5921}

1563if(mWidth!=frame.width()||mHeight!=frame.height()){
1564mWidth=frame.width();
1565mHeight=frame.height();
1566})

1155Rectframe=mWinFrame;

256finalRectmWinFrame;//framegivenbywindowmanager.

360mWinFrame=newRect();

1924privatestaticintgetRootMeasureSpec(intwindowSize,introotDimension){
1925intmeasureSpec;
1926switch(rootDimension){
1927
1928caseViewGroup.LayoutParams.MATCH_PARENT:
1929//Windowcan'tresize.ForcerootviewtobewindowSize.
1930measureSpec=MeasureSpec.makeMeasureSpec(windowSize,MeasureSpec.EXACTLY);
1931break;
1932caseViewGroup.LayoutParams.WRAP_CONTENT:
1933//Windowcanresize.Setmaxsizeforrootview.
1934measureSpec=MeasureSpec.makeMeasureSpec(windowSize,MeasureSpec.AT_MOST);
1935break;
1936default:
1937//Windowwantstobeanexactsize.Forcerootviewtobethatsize.
1938measureSpec=MeasureSpec.makeMeasureSpec(rootDimension,MeasureSpec.EXACTLY);
1939break;
1940}
1941returnmeasureSpec;
1942}

1938measureSpec=MeasureSpec.makeMeasureSpec(rootDimension,MeasureSpec.EXACTLY);

17245/**
17246*Createsameasurespecificationbasedonthesuppliedsizeandmode.
17247*
17248*Themodemustalwaysbeoneofthefollowing:
17249*<ul>
17250*<li>{@linkandroid.view.View.MeasureSpec#UNSPECIFIED}</li>
17251*<li>{@linkandroid.view.View.MeasureSpec#EXACTLY}</li>
17252*<li>{@linkandroid.view.View.MeasureSpec#AT_MOST}</li>
17253*</ul>
17254*
17255*@paramsizethesizeofthemeasurespecification
17256*@parammodethemodeofthemeasurespecification
17257*@returnthemeasurespecificationbasedonsizeandmode
17258*/
17259publicstaticintmakeMeasureSpec(intsize,intmode){
17260returnsize+mode;
17261}

1913privatevoidperformMeasure(intchildWidthMeasureSpec,intchildHeightMeasureSpec){
1914Trace.traceBegin(Trace.TRACE_TAG_VIEW,"measure");
1915try{
1916mView.measure(childWidthMeasureSpec,childHeightMeasureSpec);
1917}finally{
1918Trace.traceEnd(Trace.TRACE_TAG_VIEW);
1919}
1920}

16450/**
16451*<p>
16452*Thisiscalledtofindouthowbigaviewshouldbe.Theparent
16453*suppliesconstraintinformationinthewidthandheightparameters.
16454*</p>
16455*
16456*<p>
16457*Theactualmeasurementworkofaviewisperformedin
16458*{@link#onMeasure(int,int)},calledbythismethod.Therefore,only
16459*{@link#onMeasure(int,int)}canandmustbeoverriddenbysubclasses.
16460*</p>
16461*
16462*
16463*@paramwidthMeasureSpecHorizontalspacerequirementsasimposedbythe
16464*parent
16465*@paramheightMeasureSpecVerticalspacerequirementsasimposedbythe
16466*parent
16467*
16468*@see#onMeasure(int,int)
16469*/
16470publicfinalvoidmeasure(intwidthMeasureSpec,intheightMeasureSpec){
　　　　　　　　　.....................................................
16496//measureourselves,thisshouldsetthemeasureddimensionflagback
16497onMeasure(widthMeasureSpec,heightMeasureSpec);
16498mPrivateFlags3&=~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;

16522}

TheactualmeasurementworkofaviewisperformedinonMeasure()

Q01:
protectedvoidonMeasure(intwidthMeasureSpec,intheightMeasureSpec)是一个override的方法,它接收两个参数,通过字面意思,我们知道,这两个参数分别为宽度测量规格,高度测量规格,此时,我们会有一个疑问,这两个参数是从哪里来的?

通过:1639intchildWidthMeasureSpec=getRootMeasureSpec(mWidth,lp.width);//详见getRootMeasureSpec()方法的分析,onMeasure的第一个参数widthMeasureSpec就是这里的childWidthMeasureSpec,heightMeasureSpec对应childHeightMeasureSpec;

Q02:
调试结果出来,此时传入的measureSpec的值是-2147483648,到了这里,我们又会产生一个疑问,为什么是它?为什么是这个值?

那么这里的measureSpec就是MeasureSpec.makeMeasureSpec()方法的分析中,返回的size+mode;size是手机显示屏的像素宽或者高,文章上半部分中,我调试的手机像素宽是480,而且在自定义的View的布局文件中,layout_width设置成wrap_content,通过上面的分析,当设置成wrap_content时,模式为AT_MOST模式,通过文档描述,它的十进制值是-2147483648,那么size+mode就是480+(-2147483648)=-2147483168,也就是我们调试出来时,所得到的值-2147483648

)

return(measureSpec&MODE_MASK);

publicstaticintgetSize(intmeasureSpec){
return(measureSpec&~MODE_MASK);
}

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