Android Recycler View - 约束布局内的反向布局

Question

I have a RecyclerView inside a ConstraintLayout which is constrained at the top to the parent and at the bottom by an EditText . This works fine, however as soon as I set the recycler to reverseLayout=true the first item at the bottom has to be scrolled down to be fully seen if I have more items than the screen can display. The preview is exactly how it happens on a real device making me think I am missing something out of the layout.

NOTE:

If I remove the bottom constraint to the EditText in the RecyclerView from app:layout_constraintBottom_toTopOf="@id/feedMessageInput" to app:layout_constraintBottom_toBottomOf="parent" then this problem does not happen, however this is not desirable.

Xml Layout:

<?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"
    android:layout_marginStart="@dimen/margin_half"
    android:layout_marginTop="@dimen/margin_normal"
    android:layout_marginEnd="@dimen/margin_normal"
    android:layout_marginBottom="@dimen/margin_normal"
    android:background="@drawable/shp_rounded_rectangle_transparent_white_05"
    tools:context=".ui.messages.feed.FeedFragment">

    <ImageView
        android:id="@+id/feedEmptyImageView"
        android:layout_width="@dimen/icon_size_xxxxxlarge"
        android:layout_height="@dimen/icon_size_xxxxxlarge"
        android:contentDescription="@string/no_recipients_image"
        android:src="@drawable/ic_messages_124dp"
        android:visibility="gone"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:visibility="visible" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/feedRecycler"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginStart="@dimen/margin_triple"
        android:layout_marginEnd="@dimen/margin_half"
        android:scrollbars="vertical"
        app:layoutManager="android.support.v7.widget.LinearLayoutManager"
        app:layout_constraintBottom_toTopOf="@id/feedMessageInput"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:reverseLayout="true"
        tools:itemCount="5"
        tools:listitem="@layout/row_message" />

    <de.hdodenhof.circleimageview.CircleImageView
        android:id="@+id/feedRecipient"
        android:layout_width="@dimen/icon_size_medium"
        android:layout_height="@dimen/icon_size_medium"
        app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="@dimen/margin_normal"
        app:layout_constraintTop_toTopOf="@id/feedMessageInput"
        app:layout_constraintBottom_toBottomOf="@id/feedMessageInputView"
        app:layout_constraintEnd_toStartOf="@id/feedMessageInputView"
        app:layout_constraintHorizontal_bias="0"
        tools:src="@tools:sample/avatars" />

    <View
        android:id="@+id/feedMessageInputView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@drawable/shp_rounded_rectangle_transparent_white_10"
        android:maxHeight="@dimen/message_background_input_max_height"
        app:layout_constraintBottom_toBottomOf="@id/feedMessageInput"
        app:layout_constraintEnd_toEndOf="@id/feedMessageInput"
        app:layout_constraintStart_toStartOf="@id/feedMessageInput"
        app:layout_constraintTop_toTopOf="@id/feedMessageInput" />

    <EditText
        android:id="@+id/feedMessageInput"
        style="@style/MessagingEditText.NoUnderline"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/margin_normal"
        android:importantForAutofill="no"
        android:inputType="textMultiLine"
        android:maxLength="@integer/max_message_length"
        android:padding="@dimen/margin_half"
        android:textSize="@dimen/message_input_text_size"
        app:layout_constrainedHeight="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@id/feedSelectTemplate"
        app:layout_constraintHeight_max="@dimen/message_background_input_max_height"
        app:layout_constraintHeight_min="@dimen/message_background_input_height"
        app:layout_constraintStart_toEndOf="@id/feedRecipient"
        app:layout_constraintTop_toBottomOf="@id/feedRecycler"
        tools:hint="Send message to +447445343433"
        tools:ignore="LabelFor" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/feedSendMessage"
        style="@style/MessagingFloatingActionButton.Small"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="@dimen/margin_normal"
        android:src="@drawable/ic_sms_message_send_24dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@id/feedSelectTemplate"
        app:layout_constraintTop_toTopOf="@id/feedMessageInput" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/feedSelectTemplate"
        style="@style/MessagingFloatingActionButton.Small.Contrast"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="@dimen/margin_normal"
        android:src="@drawable/ic_sms_message_template_24dp"
        app:layout_constraintEnd_toStartOf="@id/feedSendMessage"
        app:layout_constraintStart_toEndOf="@id/feedMessageInput"
        app:layout_constraintTop_toTopOf="@id/feedMessageInput" />

</android.support.constraint.ConstraintLayout>

Current Incorrect preview when multiple rows that scroll off the top and bottom - which is incorrect:

How I expect reverseLayout=true to work no matter how many rows scroll off the top:

Any help with something I may have missed would be appreciated.

Answer 1

According to the documentation for ConstraintLayout :

Important: MATCH_PARENT is not recommended for widgets contained in a ConstraintLayout. Similar behavior can be defined by using MATCH_CONSTRAINT with the corresponding left/right or top/bottom constraints being set to "parent".

Why does this sort of work? My guess is that it is not really supported but has not been disabled and is probably not tested. The short answer is to use match_constraints ( 0dp ) exclusively and to avoid match_parent at all times when it comes to ConstraintLayout .

Answer 2

Faced with the same issue. It looks like ConstraintLayout issue (still is in beta). I've rewritten xml layout to use LinearLayout and it works for me. But still waiting for the fix from Google.