为CardView添加一个圆角修复工具类，如下所示：

public class CardViewUtils {

    private static final int DEFAULT_RADIUS = 2;

    public static void init(CardView cardView, float radius) {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
            cardView.setPreventCornerOverlap(false);
            cardView.setRadius(radius);
            ViewCompat.setElevation(cardView, 0);
        }
    }

    public static void init(CardView cardView) {
        init(cardView, dp2px(DEFAULT_RADIUS));
    }

    private static float dp2px(int dp) {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp,
                Resources.getSystem().getDisplayMetrics());
    }
}

然后在你的Activity或Fragment中调用该工具类的init方法即可修复CardView圆角破损问题：

CardView cardView = findViewById(R.id.cardView);
CardViewUtils.init(cardView);