怎么在Android中利用ImageView控件实现一个圆角功能

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;

import com.towatt.charge.towatt.R;

/**
 * @author Mr.lynn
 * @version 1.0

 * 图片圆角实现
 */
public class CustomImageView extends android.support.v7.widget.AppCompatImageView {
 private Paint paint;
 private Paint paintBorder;
 private Bitmap mSrcBitmap;
 /**
  * 圆角的弧度
  */
 private float mRadius;
 private boolean mIsCircle;

 public CustomImageView(final Context context) {
  this(context, null);
 }

 public CustomImageView(Context context, AttributeSet attrs) {
  this(context, attrs, R.attr.customImageViewStyle);
 }

 public CustomImageView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  TypedArray ta = context.obtainStyledAttributes(attrs,
    R.styleable.CustomImageView, defStyle, 0);
  mRadius = ta.getDimension(R.styleable.CustomImageView_radius, 0);
  mIsCircle = ta.getBoolean(R.styleable.CustomImageView_circle, false);
  int srcResource = attrs.getAttributeResourceValue(
    "http://schemas.android.com/apk/res/android", "src", 0);
  if (srcResource != 0)
   mSrcBitmap = BitmapFactory.decodeResource(getResources(),
     srcResource);
  ta.recycle();
  paint = new Paint();
  paint.setAntiAlias(true);
  paintBorder = new Paint();
  paintBorder.setAntiAlias(true);
 }

 @Override
 public void onDraw(Canvas canvas) {
  int width = canvas.getWidth() - getPaddingLeft() - getPaddingRight();
  int height = canvas.getHeight() - getPaddingTop() - getPaddingBottom();
  Bitmap image = drawableToBitmap(getDrawable());
  if (mIsCircle) {
   Bitmap reSizeImage = reSizeImageC(image, width, height);
   canvas.drawBitmap(createCircleImage(reSizeImage, width, height),
     getPaddingLeft(), getPaddingTop(), null);

  } else {

   Bitmap reSizeImage = reSizeImage(image, width, height);
   canvas.drawBitmap(createRoundImage(reSizeImage, width, height),
     getPaddingLeft(), getPaddingTop(), null);
  }
 }

 /**
  * 画圆角
  *
  * @param source
  * @param width
  * @param height
  * @return
  */
 private Bitmap createRoundImage(Bitmap source, int width, int height) {
  Paint paint = new Paint();
  paint.setAntiAlias(true);
  Bitmap target = Bitmap.createBitmap(width, height, Config.ARGB_8888);
  Canvas canvas = new Canvas(target);
  RectF rect = new RectF(0, 0, width, height);
  canvas.drawRoundRect(rect, mRadius, mRadius, paint);
  // 核心代码取两个图片的交集部分
  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
  canvas.drawBitmap(source, 0, 0, paint);
  return target;
 }

 /**
  * 画圆
  *
  * @param source
  * @param width
  * @param height
  * @return
  */
 private Bitmap createCircleImage(Bitmap source, int width, int height) {

  Paint paint = new Paint();
  paint.setAntiAlias(true);
  Bitmap target = Bitmap.createBitmap(width, height, Config.ARGB_8888);
  Canvas canvas = new Canvas(target);
  canvas.drawCircle(width / 2, height / 2, Math.min(width, height) / 2,
    paint);
  // 核心代码取两个图片的交集部分
  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
  canvas.drawBitmap(source, (width - source.getWidth()) / 2,
    (height - source.getHeight()) / 2, paint);
  return target;

 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  int width = MeasureSpec.getSize(widthMeasureSpec);
  int height = MeasureSpec.getSize(heightMeasureSpec);
  setMeasuredDimension(width, height);
 }

 /**
  * drawable转bitmap
  *
  * @param drawable
  * @return
  */
 private Bitmap drawableToBitmap(Drawable drawable) {
  if (drawable == null) {
   if (mSrcBitmap != null) {
    return mSrcBitmap;
   } else {
    return null;
   }
  } else if (drawable instanceof BitmapDrawable) {
   return ((BitmapDrawable) drawable).getBitmap();
  }
  Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(),
    drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
  Canvas canvas = new Canvas(bitmap);
  drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
  drawable.draw(canvas);
  return bitmap;
 }

 /**
  * 重设Bitmap的宽高
  *
  * @param bitmap
  * @param newWidth
  * @param newHeight
  * @return
  */
 private Bitmap reSizeImage(Bitmap bitmap, int newWidth, int newHeight) {
  int width = bitmap.getWidth();
  int height = bitmap.getHeight();
  // 计算出缩放比
  float scaleWidth = ((float) newWidth) / width;
  float scaleHeight = ((float) newHeight) / height;
  // 矩阵缩放bitmap
  Matrix matrix = new Matrix();

  matrix.postScale(scaleWidth, scaleHeight);
  return Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
 }

 /**
  * 重设Bitmap的宽高
  *
  * @param bitmap
  * @param newWidth
  * @param newHeight
  * @return
  */
 private Bitmap reSizeImageC(Bitmap bitmap, int newWidth, int newHeight) {
  int width = bitmap.getWidth();
  int height = bitmap.getHeight();
  int x = (newWidth - width) / 2;
  int y = (newHeight - height) / 2;
  if (x > 0 && y > 0) {
   return Bitmap.createBitmap(bitmap, 0, 0, width, height, null, true);
  }

  float scale = 1;

  if (width > height) {
   // 按照宽度进行等比缩放
   scale = ((float) newWidth) / width;

  } else {
   // 按照高度进行等比缩放
   // 计算出缩放比
   scale = ((float) newHeight) / height;
  }
  Matrix matrix = new Matrix();
  matrix.postScale(scale, scale);
  return Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
 }
}