Android exoplayer上的“下一步”按钮不工作时保持禁用状态

我的exoplayer代码如下

<com.google.android.exoplayer2.ui.PlayerView
    android:id="@+id/player_view"
    android:layout_width="match_parent"
    android:layout_height="250dp"
    android:background="#fff"
    android:focusable="true"
    app:controller_layout_id="@layout/custom_controls"
    app:fastforward_increment="10000"
    app:hide_on_touch="true"
    app:player_layout_id="@layout/exo_simple_player_view"
    app:resize_mode="fill"
    app:rewind_increment="10000"
    app:show_timeout="5000"
    app:use_controller="true"
    />

exo_下一个btn保持禁用状态。未应用单击侦听器。我不明白为什么。是否有其他地方可以禁用此btn表单。exo_prev btn工作正常。请帮我找出我做错了什么

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
android:layoutDirection="ltr"
android:background="#CC000000"
android:orientation="vertical">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:paddingTop="4dp"
    android:orientation="horizontal">

    <ImageButton android:id="@id/exo_prev"
        style="@style/ExoMediaButton.Previous"/>

    <ImageButton
        android:id="@id/exo_rew"
        style="@style/ExoMediaButton.Rewind"
        android:visibility="gone" />

    <ImageButton android:id="@id/exo_repeat_toggle"
        style="@style/ExoMediaButton"/>

    <ImageButton android:id="@id/exo_play"
        style="@style/ExoMediaButton.Play"/>

    <ImageButton android:id="@id/exo_pause"
        style="@style/ExoMediaButton.Pause"/>

    <ImageButton
        android:id="@id/exo_ffwd"
        style="@style/ExoMediaButton.FastForward"
        android:visibility="gone" />

    <ImageButton android:id="@id/exo_next"
        style="@style/ExoMediaButton.Next"/>

</LinearLayout>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="4dp"
    android:gravity="center_vertical"
    android:orientation="horizontal">

    <TextView android:id="@id/exo_position"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="14sp"
        android:textStyle="bold"
        android:paddingLeft="4dp"
        android:paddingRight="4dp"
        android:includeFontPadding="false"
        android:textColor="#FFBEBEBE"/>

    <com.google.android.exoplayer2.ui.DefaultTimeBar
        android:id="@id/exo_progress"
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="26dp"/>

    <TextView android:id="@id/exo_duration"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="14sp"
        android:textStyle="bold"
        android:paddingLeft="4dp"
        android:paddingRight="4dp"
        android:includeFontPadding="false"
        android:textColor="#FFBEBEBE"/>

    <FrameLayout
        android:id="@+id/exo_fullscreen_button"
        android:layout_width="32dp"
        android:layout_height="32dp"
        android:layout_gravity="right">

        <ImageView
            android:id="@+id/exo_fullscreen_icon"
            android:layout_width="18dp"
            android:layout_height="18dp"
            android:layout_gravity="center"
            android:adjustViewBounds="true"
            android:scaleType="fitCenter"
            android:src="@drawable/ic_fullscreen_expand"/>

    </FrameLayout>

</LinearLayout>

</LinearLayout>

 <merge xmlns:android="http://schemas.android.com/apk/res/android">

 <com.google.android.exoplayer2.ui.AspectRatioFrameLayout android:id="@id/exo_content_frame"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:layout_gravity="center">

  <!-- Video surface will be inserted as the first child of the content frame. -->

  <View android:id="@id/exo_shutter"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/black"/>

<ImageView android:id="@id/exo_artwork"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:scaleType="fitXY"/>

<com.google.android.exoplayer2.ui.SubtitleView android:id="@id/exo_subtitles"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

<ProgressBar android:id="@id/exo_buffering"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:indeterminate="true"
    android:layout_gravity="center"/>

<TextView android:id="@id/exo_error_message"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center"
    android:gravity="center"
    android:background="@color/exo_error_message_background_color"
    android:padding="16dp"/>

 </com.google.android.exoplayer2.ui.AspectRatioFrameLayout>

 <FrameLayout android:id="@id/exo_ad_overlay"
   android:layout_width="match_parent"
   android:layout_height="match_parent"/>

 <FrameLayout android:id="@id/exo_overlay"
  android:layout_width="match_parent"
  android:layout_height="match_parent"/>

<View android:id="@id/exo_controller_placeholder"
  android:layout_width="match_parent"
  android:layout_height="match_parent"/>

</merge>

private ImageView exo_prev, exo_next;

private void initFullscreenButton() {
  PlayerControlView controlView = playerView.findViewById(R.id.exo_controller);
  exo_prev = controlView.findViewById(R.id.exo_prev);
  exo_next = controlView.findViewById(R.id.exo_next);
  initNextandPreviousButton();
 });
private void initNextandPreviousButton() {

    if (exo_prev == null) {
        return;
    }

    if (exo_next == null) {
        return;
    }

    if (lessonList == null) {
        return;
    }

   if (currentVideoPosition == 0) {
        exo_prev.setVisibility(View.INVISIBLE);
        exo_next.setVisibility(View.VISIBLE);

    }

    if (currentVideoPosition == lessonList.size() - 1) {
        exo_next.setVisibility(View.INVISIBLE);
        exo_prev.setVisibility(View.VISIBLE);
    }
    exo_next.setOnClickListener(new View.OnClickListener() {
                                    @Override
                                    public void onClick(View view) {
                                        consolelog("onclick exo_next"+position,"ocp","v");
                                        if (currentVideoPosition == lessonList.size() - 1) {
                                            currentVideoPosition = currentVideoPosition + 1;
                              currentVideoUrl = lessonList.get(currentVideoPosition).getVideoUrl();
                                            initializePlayer();
                                            lessonAdapter.setTickVisoble(currentVideoPosition);
                                        }
                                    }
                                }
    );
    exo_prev.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            consolelog("onclick exo_prev"+position,"ocp","v");
            if(currentVideoPosition>0) {
                currentVideoPosition = currentVideoPosition - 1;
                currentVideoUrl = lessonList.get(currentVideoPosition).getVideoUrl();
                initializePlayer();
                lessonAdapter.setTickVisoble(currentVideoPosition);
            }
        }
    });
}