我们在做项目的时候会用到圆形的图片，比如用户头像，类似QQ。用户在用QQ更换头像的时候，上传的图片都是矩形的，但显示的时候确是圆形的。那么这是如何实现的呢，下面我们就来探讨下吧。

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先从本地把图片上传到服务器，然后根据URL把头像处理成圆形头像。

因为上传图片用到bmob的平台，所以要到bmob（http://www.bmob.cn）申请密钥。

效果图：

核心代码如下：

public class MainActivity extends Activity {
        private ImageView iv;
        private String appKey="";                //填写你的Application ID
        private String path=Environment.getExternalStorageDirectory()+"/11.jpeg";        //要上传的图片的路径
        public final int SIZE=2*1024;                
        protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                Bmob.initialize(this, appKey);                //初始化bmob SDK
                setContentView(R.layout.activity_main);
                initView();
        }
        private void initView() {
                // TODO Auto-generated method stub
                iv=(ImageView)findViewById(R.id.iv);
        }
        /**
         * 上传文件到bmob后台
         * */
        public void upload(View v){
                final BmobFile file=new BmobFile(new File(path));
                file.uploadblock(this, new UploadFileListener() {
                        @Override
                        public void onSuccess() {
                                // TODO Auto-generated method stub
                                Person p=new Person();
                                p.setUrl(file.getFileUrl(MainActivity.this));
                                p.save(MainActivity.this);
                                MyTask task=new MyTask();
                                task.execute(file.getFileUrl(MainActivity.this));
                                toast("上传成功 ");
                        }
                        @Override
                        public void onFailure(int arg0, String arg1) {
                                // TODO Auto-generated method stub
                                toast("上传失败 "+arg1);
                                Log.i("---------", "------error "+arg1);
                        }
                });
        }
        /**
         * 根据URL获取Bitmap
         * */
        public Bitmap getHttpBitmap(String url){
                Bitmap bitmap=null;
                URL myUrl;
                try {
                        myUrl=new URL(url);
                        HttpURLConnection conn=(HttpURLConnection)myUrl.openConnection();
                        conn.setConnectTimeout(5000);
                        conn.connect();
                        InputStream is=conn.getInputStream();
                        bitmap=BitmapFactory.decodeStream(is);
                        //把bitmap转成圆形
                        bitmap=toRoundBitmap(bitmap);
                        is.close();
                } catch (MalformedURLException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                }
                //返回圆形bitmap
                return bitmap;
        }
        /**
         * 把bitmap转成圆形
         * */
        public Bitmap toRoundBitmap(Bitmap bitmap){
                int width=bitmap.getWidth();
                int height=bitmap.getHeight();
                int r=0;
                //取最短边做边长
                if(width                        r=width;
                }else{
                        r=height;
                }
                //构建一个bitmap
                Bitmap backgroundBm=Bitmap.createBitmap(width,height,Config.ARGB_8888);
                //new一个Canvas，在backgroundBmp上画图 
                Canvas canvas=new Canvas(backgroundBm);
                Paint p=new Paint();
                //设置边缘光滑，去掉锯齿 
                p.setAntiAlias(true);
                RectF rect=new RectF(0, 0, r, r);
                //通过制定的rect画一个圆角矩形，当圆角X轴方向的半径等于Y轴方向的半径时，  
                //且都等于r/2时，画出来的圆角矩形就是圆形 
                canvas.drawRoundRect(rect, r/2, r/2, p);
                //设置当两个图形相交时的模式，SRC_IN为取SRC图形相交的部分，多余的将被去掉
                p.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
                //canvas将bitmap画在backgroundBmp上
                canvas.drawBitmap(bitmap, null, rect, p);
                return backgroundBm;
        }
        class MyTask extends AsyncTask{
  
                @Override
                protected Bitmap doInBackground(String... arg0) {
                        // TODO Auto-generated method stub
                        String url=arg0[0];
                        Bitmap bm=getHttpBitmap(url);
                        return bm;
                }
                @Override
                protected void onPostExecute(Bitmap result) {
                        // TODO Auto-generated method stub
                        iv.setImageBitmap(result);
                }
        }
        public void toast(String msg){
                Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
        }
}

恩，就是这么多了

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