小弟不知這方形是如何產生的，請大師解惑~

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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="wrap_content">

    <androidx.cardview.widget.CardView
        android:id="@+id/cardView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:foreground="?android:attr/selectableItemBackground"
        app:cardBackgroundColor="#80000000"
        app:cardCornerRadius="15dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <ImageView
                android:id="@+id/imageView"
                android:layout_width="match_parent"
                android:layout_height="200dp"
                android:scaleType="centerCrop"
                tools:ignore="ContentDescription" />

            <TextView
                android:id="@+id/textView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/imageView"
                android:layout_margin="10dp"
                android:autoLink="email|web"
                android:textColor="@color/colorWhite"
                android:textSize="16sp" />
        </RelativeLayout>

    </androidx.cardview.widget.CardView>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="20dp"
        android:orientation="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/cardView"
        tools:ignore="UselessLeaf">
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

更新:
將圓角去除就消失了，但還是希望有圓角，希望各位解答。