Android实现圆角图片

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".MainActivity">

  <ImageView
    android:id="@+id/iv_img"
    android:layout_width="300dp"
    android:layout_height="200dp"
    android:layout_marginTop="30dp"
    android:src="@mipmap/image_bg"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent"/>

  <ImageView
    android:id="@+id/iv_rect_img"
    android:layout_width="300dp"
    android:layout_height="200dp"
    android:layout_marginTop="30dp"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toBottomOf="@id/iv_img"/>

  <ImageView
    android:id="@+id/iv_circle_img"
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_marginTop="30dp"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@id/iv_rect_img"/>

</android.support.constraint.ConstraintLayout>

public class MainActivity extends AppCompatActivity {

  private ImageView ivRectImg, ivCircleImg;

  private Bitmap bitmap;
  private int width;
  private int height;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    ivRectImg = findViewById(R.id.iv_rect_img);
    ivCircleImg = findViewById(R.id.iv_circle_img);

    bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.image_bg);
    width = bitmap.getWidth();
    height = bitmap.getHeight();

    rectRoundBitmap();
    circleBitmap();
  }

 // 圆角矩形
  private void rectRoundBitmap() {
    RoundedBitmapDrawable bitmapDrawable = RoundedBitmapDrawableFactory.create(getResources(), bitmap);
    bitmapDrawable.setAntiAlias(true);
    bitmapDrawable.setCornerRadius(50);
    ivRectImg.setImageDrawable(bitmapDrawable);
  }

  // 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
  private void circleBitmap() {
    Bitmap circle = null;
    int min = Math.min(width, height);
    int max = Math.max(width, height);
    if (width == height) {
      circle = Bitmap.createBitmap(bitmap, 0, 0, width, height);
    } else {
      // 居中裁剪
      if (width > height) {
        circle = Bitmap.createBitmap(bitmap, (max - min) / 2, 0, min, min);
      } else {
        circle = Bitmap.createBitmap(bitmap, 0, (max - min) / 2, min, min);
      }
    }
    RoundedBitmapDrawable bitmapDrawable = RoundedBitmapDrawableFactory.create(getResources(), circle);
    bitmapDrawable.setCornerRadius(min / 2);
    bitmapDrawable.setAntiAlias(true);
    ivCircleImg.setImageDrawable(bitmapDrawable);
  }
}