效果圖：

頁面代碼：

public class CircleView extends ImageView {
    private Paint mPaint = new Paint();

    public CircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        Drawable mDrawable = getDrawable();//獲取xml文件設置的圖片
 

        if (null == mDrawable) super.onDraw(canvas);//假設為空，交給父類處理
        Bitmap mBitmap = ((BitmapDrawable) mDrawable).getBitmap();//將圖片轉化成bitmap

        int len = getWidth() < getHeight() ?
 getWidth() : getHeight();//獲取xml的長寬屬性值，選擇較小的

        Bitmap tempBitmap = Bitmap.createBitmap(len, len, Bitmap.Config.ARGB_8888);//新建一個bitmap對象。作為緩存
 

        Canvas mCanvas = new Canvas(tempBitmap);//新建畫布緩存bitmap對象

        mPaint.setAntiAlias(true);//抗鋸齒
        mCanvas.drawCircle(len / 2, len / 2, len / 2, mPaint);//畫一個圓

        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));//設置畫筆的覆蓋類型

        Matrix matrix = new Matrix(); // 初始化Matrix對象
 

        matrix.setScale((float) len / mBitmap.getWidth(), (float) len / mBitmap.getHeight()); //設置縮放比例
        mCanvas.drawBitmap(mBitmap, matrix, mPaint);//畫出縮放後的圖片

        mPaint.reset();//重置畫筆
        canvas.drawBitmap(tempBitmap, 0, 0, mPaint);//繪制緩存圖片
    }

}

超簡潔代碼實現CircleImageView