绘制流程：

1.根据获取的属性值，判断显示模式，并设置圆形图片、外边框、内边框的半径值

2.画边框

3.画图片内容

（1）获取原图

（2）得到正方形图

（3）得到缩放图

（4）得到圆形图

public class MyRoundImageView extends ImageView {
   private int defaultColor = 0xffffffff;     private ShowType mShowType = ShowType.NoBorder;     private int mBorderThickness = 0;     private int mBorderInsideColor;     private int mBorderOutsideColor;     private int mRadius = 0;     enum ShowType {
   InsideBorder, OutsideBorder, InsideAndOutsideBorder, NoBorder } public MyRoundImageView(Context context) {
   super(context); } public MyRoundImageView(Context context, AttributeSet attrs) {
   super(context, attrs); readAttrs(attrs); } public MyRoundImageView(Context context, AttributeSet attrs, int defStyleAttr) {
   super(context, attrs, defStyleAttr); readAttrs(attrs); } private void readAttrs(AttributeSet attrs) {
           TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.RoundImageView); mBorderThickness = a.getDimensionPixelSize(R.styleable.RoundImageView_border_thickness, 0); mBorderInsideColor = a.getColor(R.styleable.RoundImageView_border_inside_color, defaultColor); mBorderOutsideColor = a.getColor(R.styleable.RoundImageView_border_outside_color, defaultColor); readShowType(); } private void readShowType() {
   if (mBorderInsideColor != defaultColor && mBorderOutsideColor != defaultColor) {
   mShowType = ShowType.InsideAndOutsideBorder; } else if (mBorderInsideColor != defaultColor && mBorderOutsideColor == defaultColor) {
   mShowType = ShowType.InsideBorder; } else if (mBorderInsideColor == defaultColor && mBorderOutsideColor != defaultColor) {
   mShowType = ShowType.OutsideBorder; } else {
   mShowType = ShowType.NoBorder; }     } @Override protected void onDraw(Canvas canvas) {
   switch (mShowType) {
   case InsideBorder: mRadius = (getWidth() < getHeight() ? getWidth() : getHeight()) / 2 - mBorderThickness; drawRoundBorder(canvas, mRadius + mBorderThickness / 2, mBorderInsideColor);                 break;             case OutsideBorder: mRadius = (getWidth() < getHeight() ? getWidth() : getHeight()) / 2 - mBorderThickness; drawRoundBorder(canvas, mRadius + mBorderThickness / 2, mBorderOutsideColor);                 break;             case InsideAndOutsideBorder: mRadius = (getWidth() < getHeight() ? getWidth() : getHeight()) / 2 - mBorderThickness * 2; drawRoundBorder(canvas, mRadius + mBorderThickness / 2, mBorderInsideColor); drawRoundBorder(canvas, mRadius + mBorderThickness / 2 + mBorderThickness, mBorderOutsideColor);                 break;             case NoBorder: mRadius = (getWidth() < getHeight() ? getWidth() : getHeight()) / 2;                 break;             default:         }         drawBitmapContent(canvas); } private void drawRoundBorder(Canvas canvas, int radius, int color) {
           Paint paint = new Paint(); paint.setAntiAlias(true); paint.setFilterBitmap(true); paint.setDither(true); paint.setColor(color); paint.setStyle(Paint.Style.STROKE); paint.setStrokeWidth(mBorderThickness); canvas.drawCircle(getWidth() / 2, getHeight() / 2, radius, paint); } private void drawBitmapContent(Canvas canvas) {
           canvas.drawBitmap(bitmapToRound(bitmapToScale(bitmapToSquare(readBitmap()))), getWidth() / 2 - mRadius, getHeight() / 2 - mRadius, null); } private Bitmap readBitmap() {
           Drawable drawable = getDrawable();         if (drawable == null) {
   return null; } if (drawable instanceof NinePatchDrawable) {
   return null; } if (drawable instanceof BitmapDrawable) {
   return ((BitmapDrawable) drawable).getBitmap().copy(Bitmap.Config.ARGB_8888, true); } return null; } private Bitmap bitmapToSquare(Bitmap bitmap) {
   int w = bitmap.getWidth();         int h = bitmap.getHeight();         int x = w > h ? (w - h) / 2 : 0;         int y = w > h ? 0 : (h - w) / 2;         int sideLength = w > h ? h : w;         return Bitmap.createBitmap(bitmap, 0, 0, sideLength, sideLength); } private Bitmap bitmapToScale(Bitmap bitmap) {
   return Bitmap.createScaledBitmap(bitmap, mRadius * 2, mRadius * 2, true); } public Bitmap bitmapToRound(Bitmap bitmap) {
           Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Bitmap.Config.ARGB_8888); Canvas canvas = new Canvas(output); Paint paint = new Paint(); Rect rect = new Rect(0, 0, output.getWidth(),output.getHeight()); paint.setAntiAlias(true); canvas.drawRoundRect(new RectF(rect), rect.width()/2, rect.height()/2, paint); //取output的图层与bitmap的图层的交集 paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); //参数2是截取原图区域，可以不是全部图片，参数3是显示位置区域 canvas.drawBitmap(bitmap, rect, rect, paint);         return output; } }

附1.设置两张图片相交时的模式

/**      * setXfermode 设置两张图片相交时的模式 */ //    PorterDuff.Mode.CLEAR 清除画布上图像 //    PorterDuff.Mode.SRC 显示上层图像 //    PorterDuff.Mode.DST 显示下层图像 //    PorterDuff.Mode.SRC_OVER上下层图像都显示，上层居上显示 //    PorterDuff.Mode.DST_OVER 上下层都显示,下层居上显示 //    PorterDuff.Mode.SRC_IN 取两层图像交集部门,只显示上层图像 //    PorterDuff.Mode.DST_IN 取两层图像交集部门,只显示下层图像 //    PorterDuff.Mode.SRC_OUT 取上层图像非交集部门 //    PorterDuff.Mode.DST_OUT 取下层图像非交集部门 //    PorterDuff.Mode.SRC_ATOP 取下层图像非交集部门与上层图像交集部门 //    PorterDuff.Mode.DST_ATOP 取上层图像非交集部门与下层图像交集部门 //    PorterDuff.Mode.XOR 取两层图像的非交集部门

参考资料：