Recyclerview：第一项的底部边距未显示

Question

我在应用程序中实现了一个recyclreview，我所面临的问题是recycerview的第一项缺少边距底部，因此第一个元素看起来很难看，而其他所有元素都可以正常显示底部元素

这是项目的xml：

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
xmlns:fresco="http://schemas.android.com/apk/res-auto">

<androidx.cardview.widget.CardView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginStart="@dimen/_15sdp"
    android:layout_marginEnd="@dimen/_15sdp"
    android:layout_marginTop="@dimen/_10sdp"
    app:cardElevation="1dp"
    android:layout_marginBottom="@dimen/_10sdp"
    card_view:cardBackgroundColor="@color/white">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">


        <com.facebook.drawee.view.SimpleDraweeView
            android:id="@+id/book_avatar"
            android:layout_width="@dimen/_80sdp"
            android:layout_height="@dimen/_120sdp"
            android:layout_marginStart="16dp"
            android:layout_marginTop="24dp"
            android:layout_marginBottom="24dp"
            android:src="@drawable/ic_loading"
            fresco:actualImageScaleType="centerCrop"
            fresco:progressBarImage="@drawable/ic_loading"
            fresco:progressBarAutoRotateInterval="1300"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/popular_book_name"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="32dp"
            android:layout_marginEnd="8dp"
            android:text="@{item.title}"
            android:textColor="@color/black"
            android:textSize="@dimen/_14sdp"
            android:textStyle="bold"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.101"
            app:layout_constraintStart_toEndOf="@+id/book_avatar"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginTop="4dp"
            android:text="@string/author_"
            android:textColor="@color/black"
            app:layout_constraintStart_toEndOf="@+id/book_avatar"
            app:layout_constraintTop_toBottomOf="@+id/popular_book_name" />

        <TextView
            android:id="@+id/txt_author"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="4dp"
            android:layout_marginTop="4dp"
            android:text="@{item.author}"
            android:textColor="@color/black"
            app:layout_constraintStart_toEndOf="@+id/textView2"
            app:layout_constraintTop_toBottomOf="@+id/popular_book_name"
            tools:ignore="MissingConstraints" />

        <TextView
            android:id="@+id/txt_genre"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="4dp"
            android:layout_marginEnd="8dp"
            android:background="@drawable/rounded_btn_grey"
            android:text="@{item.genre_name}"
            android:paddingStart="@dimen/_5sdp"
            android:paddingEnd="5dp"
            android:padding="@dimen/_3sdp"
            android:textSize="@dimen/_10sdp"
            android:textColor="@color/font_color"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.057"
            app:layout_constraintStart_toEndOf="@+id/book_avatar"
            app:layout_constraintTop_toBottomOf="@+id/textView2" />


        <com.iarcuschin.simpleratingbar.SimpleRatingBar
            android:id="@+id/rating"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginTop="4dp"
            app:layout_constraintStart_toEndOf="@+id/book_avatar"
            app:layout_constraintTop_toBottomOf="@+id/txt_genre"
            app:srb_borderColor="@color/yellow"
            app:srb_fillColor="@color/yellow"
            app:srb_isIndicator="true"
            app:srb_numberOfStars="5"
            app:srb_rating="1"
            app:srb_starCornerRadius="5"
            app:srb_starSize="@dimen/_15sdp"
            app:srb_stepSize="0.5" />

        <Button
            android:id="@+id/read_btn"
            android:layout_width="@dimen/_100sdp"
            android:layout_height="@dimen/_25sdp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="10dp"
            android:layout_marginEnd="8dp"
            android:background="@drawable/rounded_btn"
            android:elevation="100dp"
            android:shadowColor="@color/colorPrimary"
            android:text="@string/view_details"
            android:textAllCaps="false"
            android:textColor="@color/white"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.08"
            app:layout_constraintStart_toEndOf="@+id/book_avatar"
            app:layout_constraintTop_toBottomOf="@+id/rating" />

        <TextView
            android:id="@+id/rate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="4dp"
            android:text="@{item.average_rating}"
            app:layout_constraintStart_toEndOf="@+id/rating"
            app:layout_constraintTop_toBottomOf="@+id/txt_genre" />


    </androidx.constraintlayout.widget.ConstraintLayout>


</androidx.cardview.widget.CardView>