代码注释很多，简单说下思路，然后直接贴代码

1、截取选定图片中间区域（宽等于高的正方形）

2、按照控件大小进行缩放

3、画圆，设置paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));

4、画图

package com.dyk.thebest.view;import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff.Mode;
import android.graphics.PorterDuffXfermode;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.ImageView;/*** 自定义圆形图片* <p>* 在<u><font color="#0000ff">onMeasure()</font></u>中强制设置控件的宽高一致 <br/>* 在<u><font color="#0000ff">getCroppedBitmap()</font></u>中截取图片中间区域并返回一个bitmap对象* * @author 一口仨馍**/
public class RoundImageView extends ImageView {public RoundImageView(Context context, AttributeSet attrs) {super(context, attrs);}public RoundImageView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);// 强制设置圆形图片控件的宽高一致int min = Math.min(getMeasuredWidth(), getMeasuredHeight());setMeasuredDimension(min, min);}@Overrideprotected void onDraw(Canvas canvas) {Drawable drawable = getDrawable();if (drawable == null) {return;}if (getWidth() == 0 || getHeight() == 0) {return;}// 注意：此条语句不能智能提示，只能手动输入Bitmap b = ((BitmapDrawable) drawable).getBitmap();if (null == b) {return;}Bitmap bitmap = b.copy(Bitmap.Config.ARGB_8888, true);// 因为后来在onMeasure中强制设置了控件宽高相等，所以相当于下面的w强制等于h// min == w == h == sbmp.getWidth() == sbmp.getHeight()是成立的int w = getWidth(), h = getHeight();int min = Math.min(w, h);Bitmap roundBitmap = getCroppedBitmap(bitmap, min);canvas.drawBitmap(roundBitmap, 0, 0, null);}/*** 截取bmp中间区域的图像，并缩放至与视图宽高大小一致。画图。* * @param bmp*            Bitmap对象* @param min*            视图宽高的最小值，单位：px* @return bitmap*/public static Bitmap getCroppedBitmap(Bitmap bmp, int min) {// 截取后的bitmapBitmap squareBitmap;int bmpWidth = bmp.getWidth();int bmpHeight = bmp.getHeight();int squareWidth = 0, squareHeight = 0;int x = 0, y = 0;if (bmpHeight > bmpWidth) {// 高大于宽squareWidth = squareHeight = bmpWidth;x = 0;y = (bmpHeight - bmpWidth) / 2;// 截取正方形图片squareBitmap = Bitmap.createBitmap(bmp, x, y, squareWidth,squareHeight);} else if (bmpHeight < bmpWidth) {// 宽大于高squareWidth = squareHeight = bmpHeight;x = (bmpWidth - bmpHeight) / 2;y = 0;squareBitmap = Bitmap.createBitmap(bmp, x, y, squareWidth,squareHeight);} else {squareBitmap = bmp;}Bitmap sbmp;//对截取后的squareBitmap缩放至控件宽高if (squareBitmap.getWidth() != min || squareBitmap.getHeight() != min) {sbmp = Bitmap.createScaledBitmap(squareBitmap, min, min, false);} else {sbmp = squareBitmap;}Bitmap output = Bitmap.createBitmap(sbmp.getWidth(), sbmp.getHeight(),Config.ARGB_8888);Canvas canvas = new Canvas(output);final Paint paint = new Paint();//指定抠图/画图区域final Rect rect = new Rect(0, 0, sbmp.getWidth(), sbmp.getHeight());paint.setAntiAlias(true);paint.setFilterBitmap(true);paint.setDither(true);canvas.drawARGB(0, 0, 0, 0);//将内容以外的区域设置为完全透明的黑色paint.setColor(Color.parseColor("#BAB399"));canvas.drawCircle(sbmp.getWidth() / 2 + 0.7f,sbmp.getHeight() / 2 + 0.7f, min / 2 + 0.1f, paint);paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));canvas.drawBitmap(sbmp, rect, rect, paint);return output;}
}