1. 首先，定义一个自定义的ImageView类RoundedImageView。代码如下：

public class RoundedImageView extends ImageView {

public RoundedImageView(Context context) {
    super(context);
}

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

public RoundedImageView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

@Override
protected void onDraw(Canvas canvas) {
    Path clipPath = new Path();
    int w = getWidth();
    int h = getHeight();
    clipPath.addCircle(w / 2, h / 2, Math.min(w, h) / 2, Path.Direction.CW);
    canvas.clipPath(clipPath);
    super.onDraw(canvas);
}

}

2. 在布局文件中，使用自定义的RoundedImageView替代普通的ImageView。

3. 在代码中，使用Picasso或Glide图片库加载图片到RoundedImageView中，使其呈现为圆形。代码如下：

RoundedImageView imageView = (RoundedImageView) convertView.findViewById(R.id.image_item); Picasso.with(context) .load(imageUrl) .placeholder(R.mipmap.ic_launcher) .error(R.mipmap.ic_launcher) .fit() .centerCrop() .transform(new CircleTransform()) .into(imageView);

注意，这里使用了名为CircleTransform的自定义Picasso转换类，代码如下：

public class CircleTransform implements Transformation { @Override public Bitmap transform(Bitmap source) { int size = Math.min(source.getWidth(), source.getHeight()); int x = (source.getWidth() - size) / 2; int y = (source.getHeight() - size) / 2; Bitmap squaredBitmap = Bitmap.createBitmap(source, x, y, size, size); if (squaredBitmap != source) { source.recycle(); } Bitmap bitmap = Bitmap.createBitmap(size, size, source.getConfig()); Canvas canvas = new Canvas(bitmap); Paint paint = new Paint(); BitmapShader shader = new BitmapShader(squaredBitmap, BitmapShader.TileMode.CLAMP, BitmapShader.TileMode.CLAMP); paint.setShader(shader); paint.setAntiAlias(true); float r = size / 2f; canvas.drawCircle(r, r, r, paint); squaredBitmap.recycle(); return bitmap; }

@Override
public String key() {
    return "circle";