ExpandableListView NullPointerException在组位置比组已经扩展的组扩展更高的组

Question

final ExpandableListView expandableListView = (ExpandableListView) fragView.findViewById(R.id.callLogList);
expandableListView.setGroupIndicator(null);
expandableListView.setClickable(true);
expandableListView.setOnGroupExpandListener(new ExpandableListView.OnGroupExpandListener() {
    @Override
    public void onGroupExpand(int groupPosition) {
        if (prev != -1 && prev != groupPosition) {
            expandableListView.collapseGroup(prev);
        }
        if (prev != -1 && prev != groupPosition) {
            ImageView prevTriangle = (ImageView) expandableListView.getChildAt(prev).findViewById(R.id.triangleTop);
            prevTriangle.setVisibility(View.INVISIBLE);
        }
        ImageView triangle = (ImageView) expandableListView.getChildAt(groupPosition).findViewById(R.id.triangleTop);
        if (triangle != null) {
            triangle.setVisibility(View.VISIBLE);
        }
        prev = groupPosition;
    }
});
expandableListView.setOnGroupCollapseListener(new ExpandableListView.OnGroupCollapseListener() {
    @Override
    public void onGroupCollapse(int groupPosition) {
        ImageView triangle = (ImageView) expandableListView.getChildAt(groupPosition).findViewById(R.id.triangleTop);
        triangle.setVisibility(View.INVISIBLE);
    }
});

//列表视图的XML：

<ExpandableListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="20dp"
        android:id="@+id/callLogList"
        android:divider="@android:color/transparent"
        android:dividerHeight="0dp"
        android:childDivider="@android:color/transparent"
        />

//用于子视图和父视图的XML

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="@dimen/call_log_list_item_actionset_height"
android:layout_alignParentBottom="true"
android:id="@+id/callLogListItemActionSet"
android:visibility="visible"
android:orientation="vertical"
android:padding="0dp"
>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:background="#8a8a8a"
    android:gravity="end"
    >
    <RelativeLayout
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_marginRight="20dp"
    android:layout_marginEnd="20dp"
    >

    <ImageView
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:background="@drawable/ic_call_white_48dp"
        android:layout_centerInParent="true"
        android:id="@+id/callLogListActionItemActionSetPhone"
        />
    </RelativeLayout>
    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_marginRight="20dp"
        android:layout_marginEnd="20dp"
        >
        <ImageView
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:background="@drawable/contact_circle_white"
            android:id="@+id/callLogListItemActionSetPerson"
            android:layout_centerVertical="true"
            android:layout_centerInParent="true"
            />
    </RelativeLayout>
    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_marginRight="10dp"
        android:layout_marginEnd="10dp">
        <ImageView
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:background="@drawable/ic_log_entry_white"
            android:id="@+id/callLogDetailLink"
            android:layout_centerVertical="true"
            android:layout_centerInParent="true"
            />
    </RelativeLayout>
</LinearLayout>

<ImageView
    android:layout_width="22dp"
    android:layout_height="22dp"
    android:src="@drawable/log_detail_navbar_triangle_bottom"
    />

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="wrap_content" android:background="@android:color/transparent">

<ImageView
    android:id="@+id/triangleTop"
    android:visibility="invisible"
    android:layout_width="22dp"
    android:layout_height="22dp"
    android:layout_marginTop="45dp"
    android:src="@drawable/log_detail_navbar_triangle_top"
    />
<!-- Contact Image -->
<ImageView
    android:layout_width="40dp"
    android:layout_height="40dp"
    android:id="@+id/callLogImage"
    android:src="@drawable/ic_contact_grey"
    android:layout_alignParentTop="true"
    />

<!-- Contact Name -->
<TextView
    android:layout_width="wrap_content"
    android:layout_height="30dp"
    android:text="First Middle Last"
    android:textSize="15sp"
    android:textColor="@android:color/white"
    android:background="@android:color/transparent"
    android:singleLine="true"
    android:paddingLeft="15dp"
    android:layout_toRightOf="@+id/callLogImage"
    android:id="@+id/callLogName"
    android:paddingTop="7dp"
    />
<!-- Call Time -->
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="12:00 PM"
    android:textColor="@android:color/white"
    android:layout_below="@+id/callLogName"
    android:layout_toRightOf="@+id/callLogImage"
    android:paddingLeft="15dp"
    android:textSize="13sp"
    android:id="@+id/callLogDate"
    />
<!-- Call Number -->
<TextView
    android:layout_width="wrap_content"
    android:layout_height="30dp"
    android:text="(111) 111-1111"
    android:textColor="@color/white"
    android:layout_alignParentTop="true"
    android:layout_alignParentRight="true"
    android:layout_marginRight="7dp"
    android:singleLine="true"
    android:paddingTop="7dp"
    android:id="@+id/callLogNumber"
    />
<!-- Call Duration -->
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="5 min 10 sec"
    android:textColor="@color/white"
    android:id="@+id/callLogDuration"
    android:layout_below="@+id/callLogNumber"
    android:layout_alignParentRight="true"
    android:layout_marginRight="7dp"
    android:singleLine="true"
    />


<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="@dimen/call_log_list_item_actionset_height"
    android:layout_alignParentBottom="true"
    android:background="@color/background_material_light"
    android:id="@+id/callLogListItemActionSet"
    android:visibility="gone"
    >
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        >
        <ImageView
            android:layout_width="24dp"
            android:layout_height="24dp"
            android:background="@drawable/ic_call_blue600_24dp"
            android:layout_centerInParent="true"
            />
    </RelativeLayout>
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        >
        <ImageView
            android:layout_width="24dp"
            android:layout_height="24dp"
            android:background="@drawable/ic_person_blue600_24dp"
            android:layout_centerVertical="true"
            android:layout_centerInParent="true"
            />
    </RelativeLayout>
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        >
        <ImageView
            android:layout_width="24dp"
            android:layout_height="24dp"
            android:background="@drawable/ic_note_add_blue600_24dp"
            android:layout_centerVertical="true"
            android:layout_centerInParent="true"
            />
    </RelativeLayout>
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        >
        <ImageView
            android:layout_width="24dp"
            android:layout_height="24dp"
            android:background="@drawable/ic_attach_file_blue600_24dp"
            android:layout_centerVertical="true"
            android:layout_centerInParent="true"
            />
    </RelativeLayout>


    </LinearLayout>

这是我的代码。我试图在父视图中定位ImageView并在可见/不可见之间切换。除了扩展比在其上方扩展的父级低一个位置的父级之外，它的效果很好。此时，ImageView引用为null，但仅限于此情况。

**当我说父母较低时，我的意思是它的小组位置高一个，或者上一个+ 1。