1.因为Android Studio没有提供xml里面的圆形style，要想显示圆形的ImageView，就只能通过...java来加工咯：

1.1 你得获得图像数据，通过R.drawable.xxx这个返回的id值来获取Bitmap，获得Bitmap，你才能够绘制ImageView

public Bitmap getDrawAblePath(int id){

        Uri uri =  Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE + "://"
                + getResources().getResourcePackageName(id) + "/"
                + getResources().getResourceTypeName(id) + "/"
                + getResources().getResourceEntryName(id));
        Bitmap bitmap = null;
        try {
            bitmap = MediaStore.Images.Media.getBitmap(this.getContentResolver(), uri);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return bitmap;

    }

1.2 重写ImageView：

package custom_view;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PaintFlagsDrawFilter;
import android.graphics.Path;
import android.graphics.Region;
import android.widget.ImageView;

public class CircleView extends android.support.v7.widget.AppCompatImageView {

    Path path;
    public PaintFlagsDrawFilter mPaintFlagsDrawFilter;// 毛边过滤
    Paint paint;
    public CircleView(Context context) {
        super(context);
        init();
    }
    public void init(){
        mPaintFlagsDrawFilter = new PaintFlagsDrawFilter(0,
                Paint.ANTI_ALIAS_FLAG|Paint.FILTER_BITMAP_FLAG);
        paint = new Paint();
        paint.setAntiAlias(true);
        paint.setFilterBitmap(true);
        paint.setColor(Color.WHITE);

    }
    @Override
    protected void onDraw(Canvas cns) {
        // TODO Auto-generated method stub
        float h = getMeasuredHeight()- 3.0f;
        float w = getMeasuredWidth()- 3.0f;
        if (path == null) {
            path = new Path();
            path.addCircle(
                    w/2.0f
                    , h/2.0f
                    , (float) Math.min(w/2.0f, (h / 2.0))
                    , Path.Direction.CCW);
            path.close();
        }
        cns.drawCircle(w/2.0f, h/2.0f,  Math.min(w/2.0f, h / 2.0f) + 1.5f, paint);
        int saveCount = cns.getSaveCount();
        cns.save();
        cns.setDrawFilter(mPaintFlagsDrawFilter);
        cns.clipPath(path,Region.Op.REPLACE);
        cns.setDrawFilter(mPaintFlagsDrawFilter);
        cns.drawColor(Color.WHITE);
        super.onDraw(cns);
        cns.restoreToCount(saveCount);
    }
}