Android实现圆形Imageview，带白色边框

public class RoundImageView extends ImageView {

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

    public RoundImageView(Context context) {
        super(context);
        init();
    }

    private final RectF roundRect = new RectF();
    private float rect_adius = 90;
    private final Paint maskPaint = new Paint();
    private final Paint zonePaint = new Paint();

    private void init() {
        maskPaint.setAntiAlias(true);
        maskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        maskPaint.setFilterBitmap(true);
        zonePaint.setAntiAlias(true);
        zonePaint.setColor(Color.WHITE);
        zonePaint.setFilterBitmap(true);
        float density = getResources().getDisplayMetrics().density;
        rect_adius = rect_adius * density;
    }

    public void setRectAdius(float adius) {
        rect_adius = adius;
        invalidate();
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right,
            int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        int w = getWidth();
        int h = getHeight();
        roundRect.set(0, 0, w, h);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.saveLayer(roundRect, zonePaint, Canvas.ALL_SAVE_FLAG);
        canvas.drawRoundRect(roundRect, rect_adius, rect_adius, zonePaint);
        //
        canvas.saveLayer(roundRect, maskPaint, Canvas.ALL_SAVE_FLAG);
        super.draw(canvas);
        canvas.restore();
    }

}

 <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_centerVertical="true"
        android:gravity="center_vertical" >

        <com.example.view.RoundImageView
            android:id="@+id/img_user_icon"
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:layout_centerHorizontal="true"
            android:scaleType="centerCrop"
            android:src="@drawable/user_icon" />

        <ImageView
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:layout_centerHorizontal="true"
            android:background="@drawable/usericon_bg_circle" />
    </RelativeLayout>

<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >

    <solid android:color="#00000000" />

    <corners android:radius="90dp" />

    <stroke
        android:width="2dp"
        android:color="#fff" />

</shape>