https://blog.csdn.net/u010784887/article/details/57075280

在开发过程中有时需要将图片显示成圆角图片，一般我们可以通过在xml中设置drawable shape即可，但今天我给出另一种方法，用java代码动态去设置圆角，顺便做个简单的笔记。 
主要原理是使用系统自带api：

RoundedBitmapDrawableFactory

简单的实现类

public class MainActivity extends AppCompatActivity {

    private ImageView mImgRectRound;
    private ImageView mImgRound;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mImgRectRound = (ImageView) findViewById(R.id.img_rect_rounded);
        mImgRound = (ImageView) findViewById(R.id.img_rounded);
        rectRoundBitmap();
        roundBitmap();
    }

    private void rectRoundBitmap(){
        //得到资源文件的BitMap
        Bitmap image= BitmapFactory.decodeResource(getResources(),R.drawable.dog);
        //创建RoundedBitmapDrawable对象
        RoundedBitmapDrawable roundImg =RoundedBitmapDrawableFactory.create(getResources(),image);
        //抗锯齿
        roundImg.setAntiAlias(true);
        //设置圆角半径
        roundImg.setCornerRadius(30);
        //设置显示图片
        mImgRectRound.setImageDrawable(roundImg);
    }

    private void roundBitmap(){
        //如果是圆的时候，我们应该把bitmap图片进行剪切成正方形， 然后再设置圆角半径为正方形边长的一半即可
        Bitmap image = BitmapFactory.decodeResource(getResources(), R.drawable.dog);
        Bitmap bitmap = null;
        //将长方形图片裁剪成正方形图片
        if (image.getWidth() == image.getHeight()) {
            bitmap = Bitmap.createBitmap(image, image.getWidth() / 2 - image.getHeight() / 2, 0, image.getHeight(), image.getHeight());
        } else {
            bitmap = Bitmap.createBitmap(image, 0, image.getHeight() / 2 - image.getWidth() / 2, image.getWidth(), image.getWidth());
        }
        RoundedBitmapDrawable roundedBitmapDrawable = RoundedBitmapDrawableFactory.create(getResources(), bitmap);
        //圆角半径为正方形边长的一半
        roundedBitmapDrawable.setCornerRadius(bitmap.getWidth() / 2);
        //抗锯齿
        roundedBitmapDrawable.setAntiAlias(true);
        mImgRound.setImageDrawable(roundedBitmapDrawable);
    }
}

布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.cjl.roundedbitmap.MainActivity">

    <ImageView
        android:id="@+id/img_rect_rounded"
        android:layout_width="200dp"
        android:layout_height="300dp"
        android:layout_marginTop="20dp"
        android:layout_gravity="center_horizontal"/>

    <ImageView
        android:id="@+id/img_rounded"
        android:layout_marginTop="20dp"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:layout_gravity="center_horizontal"/>
</LinearLayout>