ExpandableListView仅显示一个groupView而没有childView

Question

I'm a newbie in Android. I want to show my records in a database using an expandable list view, so that records of the same day form a group. I want something like this:

day 1   
-------------------
record 1 of day 1    
record 2 of day 1

day 2
-------------------
record 1 of day 2
record 2 of day 2
record 3 of day 2
...

But what I get is this:

day 1
-------------------

Only one record is showing as the group view, and when I expand it, nothing shows as a child.

FirstFragment.java:

public class FirstFragment extends Fragment {

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        createExpandableListView();

    } 

    private void createExpandableListView() {
        String time = Long.toString(((ShowBillBookActivity)getActivity()).book.getTime().getTimeInMillis());
        BillTableHandler handler = new BillTableHandler(getActivity(),
            ((MyApplication) getActivity().getApplication()).BILL_TABLE_NAME_PREFIX + time);
        ExpandableListView view =  (ExpandableListView) getView().findViewById(R.id.expandableListView);
        Cursor c = handler.getAllBills();
        Log.d("tag", "handler.getAllbills(): "+c.getCount());
        ExpandableListAdapter adapter = new ExpandableListAdapter(handler,
            this.getActivity(),
            handler.getAllBills(),
            R.layout.group_expandable_list_view,
            new String[]{BillEntry.DAY, BillEntry.AMOUNT},
            new int[]{R.id.textview_time, R.id.textview_extra},
            R.layout.child_expandable_list_view,
            new String[]{BillEntry.PAYER, BillEntry.AMOUNT},
            new int[]{R.id.textview_payer, R.id.textview_amount});
        view.setAdapter(adapter);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }
}

ExpandableListAdapter.java

public class ExpandableListAdapter extends SimpleCursorTreeAdapter {
    BillTableHandler handler;

    public ExpandableListAdapter(BillTableHandler handler, Context context, Cursor cursor, int groupLayout,
                             String[] groupFrom, int[] groupTo, int childLayout, String[] childFrom,
                             int[] childTo){
        super(context, cursor, groupLayout, groupFrom, groupTo, childLayout, childFrom, childTo);
        this.handler = handler;
    }

    @Override
    protected Cursor getChildrenCursor(Cursor groupCursor) {
        long time = groupCursor.getLong(groupCursor.getColumnIndexOrThrow(BillTableHandler.BillEntry.DAY));
        Cursor c = handler.getBillsOfTime(time);
        Log.d("tag","child Count : "+c.getCount());
        c.moveToFirst();
        return c;
    }
}

group_expandable_list_view.xml

<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:focusable="false"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<TextView
    android:id="@+id/textview_time"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="8dp"
    android:layout_marginTop="8dp"
    android:text="TextView"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/textview_extra"
    android:layout_width="61dp"
    android:layout_height="18dp"
    android:text="TextView"
    app:layout_constraintLeft_toRightOf="@+id/textview_time"
    android:layout_marginLeft="32dp"
    app:layout_constraintTop_toTopOf="parent"
    android:layout_marginTop="8dp" />
</android.support.constraint.ConstraintLayout>

child_expandable_list_view.xml

<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:focusable="false"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<TextView
    android:id="@+id/textview_payer"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="8dp"
    android:layout_marginTop="8dp"
    android:text="hello"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/textview_amount"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="32dp"
    android:layout_marginTop="8dp"
    android:text="world"
    app:layout_constraintLeft_toRightOf="@+id/textview_payer"
    app:layout_constraintTop_toTopOf="parent" />
<TextView
    android:id="@+id/textView5"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="32dp"
    android:text="text"
    app:layout_constraintTop_toBottomOf="@+id/textview_amount"
    android:layout_marginLeft="8dp"
    app:layout_constraintLeft_toLeftOf="parent" />
</android.support.constraint.ConstraintLayout>

I've been working on this for about a week and am getting pretty desperate. So please, any suggestion is welcome.

Answer 1

It's working now. The reason is that in the fragment layout, the ExpandableListView is nested in a ScrollView . Apparently, this is not good practice, because the size of ExpandableListView could not be correctly calculated (for more explanations see this blog , unfortunately partly in Chinese). This way, you'll find that getChildView() of the base SimpleCursorTreeAdapter never gets called. That's why the child view never gets rendered.

Solution:

1. Get rid of ScrollView , just ExpandableListView will work fine. Or

2. Extend ExpandableListView as this answer does, if you have to have it nested under ScrollView .