采用Bitmap的extractAlpha产生图片边缘光晕效果

前几天使用一款android手机测试的时候，
发现了应用的 shortcut 九宫格页面有一个点击效果，
就是当点击一个应用的icon图标的时候，会在icon的周围有荧光效果，
无论icon的形状是什么样子的都会有这样的效果,然后又想到Apidemo里面有个alphaDrawable例子
大家可以去在回顾一下，之后我就想到了会不会是使用这个extractAlpha实现的，自己就动手写了个例子
发现效果确实不错，分享给大家
主要关键点
1、设置imageview的src drawable
2、从src drawable中抽取 bitmap的alpha（只有透明度没有颜色）
3、使用bitmap的alpha填充一种颜色后生产新的bitmap
4、使用新生成的bitmap做一个statelistdrawable作为imageview的backgroud
5、这需要注意的是要跟imageview设置几个像素的padding这样才不会让src和backgroud重合






主要的代码：

/*
*Copyright(C)2009TheAndroidOpenSourceProject
*
*LicensedundertheApacheLicense,Version2.0(the"License");
*youmaynotusethisfileexceptincompliancewiththeLicense.
*YoumayobtainacopyoftheLicenseat
*
*http://www.apache.org/licenses/LICENSE-2.0
*
*Unlessrequiredbyapplicablelaworagreedtoinwriting,software
*distributedundertheLicenseisdistributedonan"ASIS"BASIS,
*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.
*SeetheLicenseforthespecificlanguagegoverningpermissionsand
*limitationsundertheLicense.
*/

packagecom.study;

importandroid.content.Context;
importandroid.content.res.TypedArray;
importandroid.graphics.Bitmap;
importandroid.graphics.Canvas;
importandroid.graphics.Color;
importandroid.graphics.Paint;
importandroid.graphics.Bitmap.Config;
importandroid.graphics.drawable.BitmapDrawable;
importandroid.graphics.drawable.StateListDrawable;
importandroid.util.AttributeSet;
importandroid.view.View;
importandroid.view.ViewGroup;
importandroid.widget.ImageView;

/**
*Alayoutthatarrangesitschildreninagrid.Thesizeofthe
*cellsissetbythe{@link#setCellSize}methodandthe
*android:cell_widthandandroid:cell_heightattributesinXML.
*Thenumberofrowsandcolumnsisdeterminedatruntime.Each
*cellcontainsexactlyoneview,andtheyflowinthenatural
*childorder(theorderinwhichtheywereadded,ortheindex
*in{@link#addViewAt}.Viewscannotspanmultiplecells.
*/
publicclassFixedGridLayoutextendsViewGroup{
intmCellWidth;
intmCellHeight;

publicFixedGridLayout(Contextcontext){
super(context);
}

publicFixedGridLayout(Contextcontext,AttributeSetattrs){
super(context,attrs);

//Readtheresourceattributes.
TypedArraya=context.obtainStyledAttributes(attrs,R.styleable.FixedGridLayout);
mCellWidth=a.getDimensionPixelSize(R.styleable.FixedGridLayout_cellWidth,-1);
mCellHeight=a.getDimensionPixelSize(R.styleable.FixedGridLayout_cellHeight,-1);
a.recycle();

}

publicvoidsetCellWidth(intpx){
mCellWidth=px;
requestLayout();
}

publicvoidsetCellHeight(intpx){
mCellHeight=px;
requestLayout();
}

@Override
protectedvoidonMeasure(intwidthMeasureSpec,intheightMeasureSpec){
intcellWidthSpec=MeasureSpec.makeMeasureSpec(mCellWidth,MeasureSpec.AT_MOST);
intcellHeightSpec=MeasureSpec.makeMeasureSpec(mCellHeight,MeasureSpec.AT_MOST);

intcount=getChildCount();
for(intindex=0;index<count;index++){
finalViewchild=getChildAt(index);
child.measure(cellWidthSpec,cellHeightSpec);
}
//Usethesizeourparentsgaveus
setMeasuredDimension(resolveSize(mCellWidth*count,widthMeasureSpec),
resolveSize(mCellHeight*count,heightMeasureSpec));
}

@Override
protectedvoidonLayout(booleanchanged,intl,intt,intr,intb){
intcellWidth=mCellWidth;
intcellHeight=mCellHeight;
intcolumns=(r-l)/cellWidth;
if(columns<0){
columns=1;
}
intx=0;
inty=0;
inti=0;
intcount=getChildCount();
for(intindex=0;index<count;index++){
finalViewchild=getChildAt(index);

intw=child.getMeasuredWidth();
inth=child.getMeasuredHeight();

intleft=x+((cellWidth-w)/2);
inttop=y+((cellHeight-h)/2);

child.layout(left,top,left+w,top+h);
if(i>=(columns-1)){
//advancetonextrow
i=0;
x=0;
y+=cellHeight;
}else{
i++;
x+=cellWidth;
}
}
}

@Override
protectedvoidonFinishInflate(){
super.onFinishInflate();
intcnt=getChildCount();
Paintp=newPaint();
p.setColor(Color.CYAN);

for(inti=0;i<cnt;i++){
Viewv=getChildAt(i);
setStateDrawable((ImageView)v,p);
}
}

privatevoidsetStateDrawable(ImageViewv,Paintp){
BitmapDrawablebd=(BitmapDrawable)v.getDrawable();
Bitmapb=bd.getBitmap();
Bitmapbitmap=Bitmap.createBitmap(bd.getIntrinsicWidth(),bd.getIntrinsicHeight(),Config.ARGB_8888);
Canvascanvas=newCanvas(bitmap);
canvas.drawBitmap(b.extractAlpha(),0,0,p); 先extractAlpha 一下，然后才可用 画笔 产生新的位图。 否则画笔不生效。

StateListDrawablesld=newStateListDrawable();
sld.addState(newint[]{android.R.attr.state_pressed},newBitmapDrawable(bitmap));

v.setBackgroundDrawable(sld);
}
}

bitmap1 bitmap2

InputStream is = context.getResources().openRawResource(R.drawable.app_sample_code);
mBitmap = BitmapFactory.decodeStream(is);
mBitmap2 = mBitmap.extractAlpha();

Paint p = new Paint();
float y = 10;

p.setColor(Color.RED);
canvas.drawBitmap(mBitmap, 10, y, p);
y += mBitmap.getHeight() + 10;
canvas.drawBitmap(mBitmap2, 10, y, p);
y += mBitmap2.getHeight() + 10;