问在约束布局中编辑文本滚动条问题

EN

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="match_parent">

    <EditText
        android:id="@+id/editFeedback"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:bufferType="spannable"
        android:gravity="top"
        android:hint="Some text"
        android:inputType="textCapSentences|textMultiLine"
        android:minHeight="120dp"
        android:overScrollMode="ifContentScrolls"
        android:scrollbarStyle="insideInset"
        android:scrollbars="vertical"
        android:selectAllOnFocus="true"
        android:textIsSelectable="true"
        android:textSize="16sp"
        app:layout_constraintBottom_toTopOf="@+id/buttonSend"
        app:layout_constraintEnd_toEndOf="@id/guidelineEnd"
        app:layout_constraintHeight_default="wrap"
        app:layout_constraintStart_toStartOf="@id/guidelineStart"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0"
        app:layout_constraintVertical_chainStyle="packed"
        tools:text="" />

    <Button
        android:id="@+id/buttonSend"
        style="@style/Widget.AppCompat.Button.Colored"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="end"
        android:text="Send"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="@+id/barrierEnd"
        app:layout_constraintEnd_toEndOf="@id/guidelineEnd"
        app:layout_constraintTop_toBottomOf="@+id/editFeedback" />

    <TextView
        android:id="@+id/Footer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="start"
        android:layout_marginBottom="100dp"
        android:text="This is a footer"
        android:textSize="15sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <android.support.constraint.Guideline
        android:id="@+id/guidelineStart"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_begin="8dp" />

    <android.support.constraint.Guideline
        android:id="@+id/guidelineEnd"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_end="8dp" />

    <android.support.constraint.Barrier
        android:id="@+id/barrierEnd"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:barrierDirection="top"
        app:constraint_referenced_ids="Footer" />

</android.support.constraint.ConstraintLayout>