layout_below无法与layout_centerVertical一起使用

Question

我一直试图在ScrollView中使用RelativeLayout来定位两个LinearLayout，一个位于顶部，一个位于中心。我用过layout_alignParentTop和layout_centerVertical。为了防止重叠，我尝试在第二个LinearLayout上使用layout_below，但它会中断layout_centerVertical，而第二个LinearLayout会返回顶部。怎么做？谢谢。

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".activities.StartFragment">
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <LinearLayout
            android:id="@+id/trial_button"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:layout_marginRight="20dp"
            android:layout_marginTop="25dp"
            android:layout_alignParentTop="true"
            android:background="@drawable/trial_border"
            android:foreground="?android:attr/selectableItemBackground"
            android:clickable="true"
            android:orientation="horizontal">
            <ImageView
                android:layout_width="wrap_content"
                android:layout_height="30dp"
                android:layout_gravity="top"
                android:layout_marginRight="10dp"
                android:layout_marginTop="3dp"
                android:layout_marginLeft="10dp"
                android:src="@drawable/ic_access_time_black_24dp" />

            <LinearLayout
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:layout_marginBottom="5dp"
                android:layout_marginTop="5dp"
                android:orientation="vertical">
                <TextView
                    android:id="@+id/trial_text"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="left|center"
                    android:text="@string/trial_exp"
                    android:textColor="@color/darkGrey"
                    android:textSize="15sp" />
                <TextView
                    android:id="@+id/trial_more"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="right|center"
                    android:text="@string/trial_exp_more"
                    android:textColor="@color/darkGreen"
                    android:layout_marginRight="10dp"
                    android:textSize="13sp" />
            </LinearLayout>
        </LinearLayout>

        <LinearLayout
            android:id="@+id/main_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/trial_button"
            android:layout_centerVertical="true"
            android:orientation="vertical">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_gravity="top"
                android:gravity="center"
                android:orientation="vertical">

                <ImageView
                    android:id="@+id/VImage"
                    android:layout_width="wrap_content"
                    android:layout_height="200sp"
                    android:src="@drawable/image_global" />

                <TextView
                    android:id="@+id/VText"
                    android:layout_width="match_parent"
                    android:layout_height="40dp"
                    android:gravity="center"
                    android:text="@string/protection_disabled"
                    android:textColor="@color/darkRed"
                    android:textSize="18sp"
                    android:textStyle="bold" />

            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_gravity="top"
                android:gravity="center"
                android:orientation="vertical">

                <com.google.android.material.button.MaterialButton
                    android:id="@+id/start_vpn_button"
                    style="@style/Widget.AppCompat.Button.Borderless.Colored"
                    android:layout_width="141dp"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="16dp"
                    android:text="@string/protect_me"
                    android:textColor="@color/white"
                    android:textStyle="bold"
                    app:backgroundTint="@color/green" />

                <com.google.android.material.button.MaterialButton
                    android:id="@+id/stop_vpn_button"
                    style="@style/Widget.AppCompat.Button.Borderless.Colored"
                    android:layout_width="141dp"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="16dp"
                    android:text="@string/unprotect_me"
                    android:textColor="@color/white"
                    android:textStyle="bold"
                    android:visibility="gone"
                    app:backgroundTint="@color/red" />
            </LinearLayout>

            <LinearLayout
                android:id="@+id/r_button"
                android:layout_width="match_parent"
                android:layout_height="45dp"
                android:layout_marginLeft="20dp"
                android:layout_marginTop="50sp"
                android:layout_marginRight="20dp"
                android:background="@drawable/single_border"
                android:clickable="true"
                android:foreground="?android:attr/selectableItemBackground"
                android:orientation="horizontal">

                <ImageView
                    android:id="@+id/r_image"
                    android:layout_width="wrap_content"
                    android:layout_height="30dp"
                    android:layout_gravity="center"
                    android:src="@drawable/image_r_50" />

                <TextView
                    android:id="@+id/r_text"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="left|center"
                    android:text="@string/r_to"
                    android:textColor="@color/darkGrey"
                    android:textSize="15sp" />
            </LinearLayout>
        </LinearLayout>
    </RelativeLayout>
</ScrollView>