Xamarin Android子方法从未在ExpandableListAdapter中调用

Question

I'm having issues with ExpandableListAdapter. I can't get the list to expand. It seems the problem is with all of these child methods: Java.Lang.Object GetChild(int groupPosition, int childPosition) public override long GetChildId(int groupPosition, int childPosition) public override View GetChildView(int groupPosition, int childPosition, bool isLastChild, View convertView, ViewGroup parent) public override int GetChildrenCount(int groupPosition)

These methods are never being called. I can't seem to figure out why. Here is my code:

ExpandableTaskListAdapter.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;

namespace MyProject
{
    public class ExpandableTaskListAdapter : BaseExpandableListAdapter
    {
        private readonly Context context;
        private readonly List<string> headers;
        private readonly Dictionary<string, List<string>> listChildData;
        private readonly LayoutInflater inflater;
        private readonly bool[] expanded;

        public ExpandableTaskListAdapter(Context context, List<string> headers, Dictionary<string, List<string>> listChildData, LayoutInflater inflater)
        {
            this.context = context;
            this.headers = headers;
            this.listChildData = listChildData;
            this.inflater = inflater;
            expanded = new bool[headers.Count];
        }

        public override void OnGroupCollapsed(int groupPosition)
        {
            expanded[groupPosition] = !expanded[groupPosition];
            base.OnGroupCollapsed(groupPosition);
        }

        public override void OnGroupExpanded(int groupPosition)
        {
            expanded[groupPosition] = !expanded[groupPosition];
            base.OnGroupExpanded(groupPosition);
        }

        public override Java.Lang.Object GetChild(int groupPosition, int childPosition)
        {
            return listChildData[headers[groupPosition]][childPosition];
        }

        public override long GetChildId(int groupPosition, int childPosition)
        {
            return childPosition;
        }

        public override View GetChildView(int groupPosition, int childPosition, bool isLastChild, View convertView, ViewGroup parent)
        {
            string childText = (string)GetChild(groupPosition, childPosition);
            convertView = inflater.Inflate(Resource.Layout.task_child, null);

            TextView listChild = convertView.FindViewById<TextView>(Resource.Id.label);
            listChild.Text = childText;

            return convertView;
        }

        public override int GetChildrenCount(int groupPosition)
        {
            return listChildData[headers[groupPosition]].Count;
        }

        public override Java.Lang.Object GetGroup(int groupPosition)
        {
            return headers[groupPosition];
        }

        public override long GetGroupId(int groupPosition)
        {
            return groupPosition;
        }

        public override View GetGroupView(int groupPosition, bool isExpanded, View convertView, ViewGroup parent)
        {
            string headerTitle = (string)GetGroup(groupPosition);

            convertView = inflater.Inflate(Resource.Layout.task_child, null);

            TextView header = convertView.FindViewById<TextView>(Resource.Id.label);
            header.Text = headerTitle;

            convertView.FindViewById<LinearLayout>(Resource.Id.main_layout).Click += (sender, e) =>
            {
                if (expanded[groupPosition])
                    OnGroupCollapsed(groupPosition);
                else
                    OnGroupExpanded(groupPosition);
            };

            return convertView;
        }

        public override int GroupCount
        {
            get { return headers.Count; }
        }

        public override bool HasStableIds
        {
            get { return true; }
        }

        public override bool IsChildSelectable(int groupPosition, int childPosition)
        {
            return true;
        }
    }
}

task_child.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_layout"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="5dp">

  <TextView
    android:id="@+id/label"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:gravity="center_vertical"
    android:layout_gravity="center_vertical"
    android:textSize="17sp"
    android:paddingLeft="40dp"/>

  <ImageView
    android:id="@+id/icon"
    android:layout_width="30dp"
    android:layout_height="30dp"
    android:layout_marginLeft="10dp"
    android:layout_marginRight="5dp"
    android:gravity="center_vertical"
    android:layout_gravity="center_vertical"
    android:background="@drawable/ic_delete"/>

  <CheckBox
    android:id="@+id/checkbox"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:gravity="center_vertical"
    android:layout_gravity="center_vertical"/>

</LinearLayout>

Putting a breakpoint in the constructor, I can see that I am passing in the correct data. Why are the child methods never being called?

Answer 1

When your GroupHeaderView is clicked the ExpandableListView invokes the OnGroupExpanded where the expanded[position] = true is set.

However, your .Click subscriber on the ListView in the GroupHeaderView is also called, where it finds the expanded[position] == true and calls the OnGroupCollapsed method. This results in the Group not being expanded at all and no requests for it's children are made.

Just remove the .Click handler in GetGroupView method and everything should work fine.

    public override View GetGroupView(int groupPosition, bool isExpanded, View convertView, ViewGroup parent)
    {
        string headerTitle = (string)GetGroup(groupPosition);

        convertView = inflater.Inflate(Resource.Layout.task_child, null);

        TextView header = convertView.FindViewById<TextView>(Resource.Id.label);
        header.Text = headerTitle;

        return convertView;
    }