Android（Xamarin）ListView位置问题

Question

我正在开发一个 ListView，它在屏幕之外填充数据（需要滚动）并面临数据重复的问题。通过一些研究，我实现了一个 ViewHolder，解决了重复数据的问题。但是，ListView 中的某些元素不适用于数据 - 而是定位 - 结果，每次我滚动视图并自行回收时，这些元素仍然会变得混乱。下面是 ListView 适配器和 ViewHolder 代码：

public class ListAdapter : BaseAdapter
   {
       private readonly Activity activity;

       public ListAdapter(Activity a)
       {
           activity = a;
       }

       public override int Count
       {
           get { return nameTexts.Length; }
       }

       public override Java.Lang.Object GetItem(int position)
       {
           return null;
       }

       public override long GetItemId(int position)
       {
           return 0;
       }

       public override View GetView(int position, View convertView, ViewGroup parent)
       {
           ViewHolder holder;
           View view = convertView;

           if (view == null)
           {
               holder = new ViewHolder();

               view = activity.LayoutInflater.Inflate(Resource.Layout.Hospital_List_Item, parent, false);
               holder.hospitalName = view.FindViewById<TextView>(Resource.Id.selectHospital_HospitalText);

               view.Click += delegate
               {
                   Intent intent = new Intent(activity, typeof(Request_Appointment));
                   intent.PutExtra("hospitalName", nameTexts[position]);
                   activity.StartActivity(intent);
               };

               //  Set alternatiing background of row
               if (position % 2 == 1)
               {
                   view.SetBackgroundResource(Resource.Color._8_white);
               }

               view.Tag = holder;
           }
           else
           {
               holder = view.Tag as ViewHolder;
           }            

           //  Set height of row
           view.LayoutParameters.Height = Select_Hospital.LIST_HEIGHT / 6;

           //  Row contents
           holder.hospitalName.Text = nameTexts[position];
           System.Diagnostics.Debug.WriteLine(position);



           return view;
       }

       private readonly string[] nameTexts =
       {
           "Hospital 1",
           "Hospital 2",
           "Hospital 3",
           "Hospital 4",
           "Hospital 5",
           "Hospital 6",
           "Hospital 7",
           "Hospital 8",
           "Hospital 9",
           "Hospital 10",
           "Hospital 11",
           "Hospital 12",
           "Hospital 13",
           "Hospital 14",
           "Hospital 15",
           "Hospital 16",
           "Hospital 17",
           "Hospital 18",
           "Hospital 19",
           "Hospital 20",
           "Hospital 21",
           "Hospital 22",
           "Hospital 23",
           "Hospital 24",
           "Hospital 25"
       };
   }

   //  ViewHolder
   class ViewHolder : Java.Lang.Object
   {
       public TextView hospitalName { get; set; }
       public ToggleButton hospitalFavourites { get; set; }
   }

Hospital_List_Item axml 代码：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <TextView
        android:id="@+id/selectHospital_HospitalText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="25dp"
        android:layout_centerVertical="true"
        android:textColor="@color/dark_blue" />
    <ToggleButton
        android:id="@+id/selectHospital_FavouritesToggle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginRight="25dp"
        android:layout_alignParentRight="true"
        android:layout_centerVertical="true" />
</RelativeLayout>

初始屏幕：

滚动后：

注意：点击任意行项会显示点击行的位置，滚动后返回错误值。

不按预期工作的元素是交替背景以及点击事件。我尝试将它们移到 if (view == null) 块之外，但这使它变得更糟。非常感谢任何帮助！

 

-编辑-

更新代码：

public class ListAdapter : BaseAdapter
{
    private readonly Activity activity;

    public ListAdapter(Activity a)
    {
        activity = a;
    }

    public override int Count
    {
        get { return nameTexts.Length; }
    }

    public override Java.Lang.Object GetItem(int position)
    {
        return null;
    }

    public override long GetItemId(int position)
    {
        return 0;
    }

    public override View GetView(int position, View convertView, ViewGroup parent)
    {
        ViewHolder holder;
        View view = convertView;
        int type;

        if (view == null)
        {
            holder = new ViewHolder();

            view = activity.LayoutInflater.Inflate(Resource.Layout.Hospital_List_Item, parent, false);
            holder.hospitalName = view.FindViewById<TextView>(Resource.Id.selectHospital_HospitalText);
            holder.hospitalFavourites = view.FindViewById<ToggleButton>(Resource.Id.selectHospital_FavouritesToggle);
            holder.position = position;
            System.Diagnostics.Debug.WriteLine(holder.position);

            view.Click += delegate
            {
                Intent intent = new Intent(activity, typeof(Request_Appointment));
                intent.PutExtra("hospitalName", holder.hospitalName.Text);
                activity.StartActivity(intent);
            };

            view.Tag = holder;
        }
        else
        {
            holder = view.Tag as ViewHolder;
        }            

        //  Set height of row
        view.LayoutParameters.Height = Select_Hospital.LIST_HEIGHT / 6;

        //  Set alternating background of row
        type = GetItemViewType(holder.position);

        if (type == 0)
        {
            view.SetBackgroundResource(Resource.Color._8_white);
        }

        //  Row contents
        holder.hospitalName.Text = nameTexts[position];

        holder.hospitalFavourites.Text = position.ToString();
        holder.hospitalFavourites.SetOnCheckedChangeListener(null);
        holder.hospitalFavourites.Click += delegate
            {
                holder.hospitalFavourites.Text = position.ToString();
            };

        return view;
    }

    //  Number of different rows
    public override int ViewTypeCount
    {
        get
        {
            return 2;
        }
    }

    //  To alternate rows
    public override int GetItemViewType(int position)
    {
        return position % 2 == 1 ? 0 : 1;
    }        

    private readonly string[] nameTexts =
    {
        "Hospital 1",
        "Hospital 2",
        "Hospital 3",
        "Hospital 4",
        "Hospital 5",
        "Hospital 6",
        "Hospital 7",
        "Hospital 8",
        "Hospital 9",
        "Hospital 10",
        "Hospital 11",
        "Hospital 12",
        "Hospital 13",
        "Hospital 14",
        "Hospital 15",
        "Hospital 16",
        "Hospital 17",
        "Hospital 18",
        "Hospital 19",
        "Hospital 20",
        "Hospital 21",
        "Hospital 22",
        "Hospital 23",
        "Hospital 24",
        "Hospital 25"
    };
}

class ViewHolder : Java.Lang.Object
{
    public TextView hospitalName { get; set; }
    public ToggleButton hospitalFavourites { get; set; }
    public int position { get; set; }
}

 

-EDIT 2- (OnClick lambda)

public class RecyclerAdapter : RecyclerView.Adapter
{
    private readonly Activity activity;
    public event EventHandler<int> ItemClick;

    public RecyclerAdapter(Activity a)
    {
        activity = a;
    }

    public override int ItemCount
    {
        get
        {
            return nameTexts.Length;
        }
    }

    private void OnClick (int position)
    {
        ItemClick?.Invoke(this, position);
    }

    private void OnItemClick(object sender, int position)
    {
        int buttonNum = position + 1;
        Toast.MakeText(activity, "This is button number " + buttonNum, ToastLength.Short).Show();
    }

    public override long GetItemId(int position)
    {
        return position;
    }

    public override int GetItemViewType(int position)
    {
        return position % 2 == 1 ? 0 : 1;
    }

    public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
    {
        ViewHolder vh = holder as ViewHolder;

        //  Set height of row
        vh.ItemView.LayoutParameters.Height = Select_Hospital.LIST_HEIGHT / 6;

        //  Set alternating background of row
        int type = GetItemViewType(position);

        if (type == 0)
        {
            vh.ItemView.SetBackgroundResource(Resource.Color._8_white);
        }

        vh.hospitalName.Text = nameTexts[position];
    }

    public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
    {
        View view = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.sublayout_Hospital_List_Item, parent, false);
        ViewHolder holder = new ViewHolder(view, OnClick);

        holder.ItemView.Click += delegate
        {
            Intent intent = new Intent(activity, typeof(Request_Appointment));
            intent.PutExtra("hospitalName", holder.hospitalName.Text);
            activity.StartActivity(intent);
        };

        ItemClick += OnItemClick;

        return holder;
    }

    private readonly string[] nameTexts =
    {
        "Hospital 1",
        "Hospital 2",
        "Hospital 3",
        "Hospital 4",
        "Hospital 5",
        "Hospital 6",
        "Hospital 7",
        "Hospital 8",
        "Hospital 9",
        "Hospital 10",
        "Hospital 11",
        "Hospital 12",
        "Hospital 13",
        "Hospital 14",
        "Hospital 15",
        "Hospital 16",
        "Hospital 17",
        "Hospital 18",
        "Hospital 19",
        "Hospital 20",
        "Hospital 21",
        "Hospital 22",
        "Hospital 23",
        "Hospital 24",
        "Hospital 25"
    };
}

class ViewHolder : RecyclerView.ViewHolder
{
    public TextView hospitalName { get; set; }
    public ToggleButton hospitalFavourites { get; set; }

    public ViewHolder (View view, Action<int> listener) : base(view)
    {
        hospitalName = view.FindViewById<TextView>(Resource.Id.selectHospital_HospitalText);
        hospitalFavourites = view.FindViewById<ToggleButton>(Resource.Id.selectHospital_FavouritesToggle);

        hospitalFavourites.Click += (sender, e) => listener(AdapterPosition);
    }
}

Answer 1

不应该是你的getItem() 看起来像这样：

    public override Java.Lang.Object GetItem(int position){
        return nameTexts[position];
    }

Answer 2

1. HospitalFavourites ToggleButton 未在 GetView 方法中分配

2. view.Click 委托应该从视图中检索标签，而不是访问 nameTexts[position]。您可以将位置作为属性添加到 ViewHolder 中，以便在单击列表项时访问它。

3. 用于交替背景颜色的代码应位于 if (view == null) 块之外。

== 已编辑 ==

使用下面的代码来修改你想要做的事情。

using System;
using Android.App;
using Android.Views;
using Android.Widget;

namespace ListAdapterSample.Droid
{
public class ListAdapter : BaseAdapter
{
    private readonly Activity activity;

    public ListAdapter(Activity a)
    {
        activity = a;
    }

    public override int Count
    {
        get { return nameTexts.Length; }
    }

    public override Java.Lang.Object GetItem(int position)
    {
        return null;
    }

    public override long GetItemId(int position)
    {
        return 0;
    }

    public override View GetView(int position, View convertView, ViewGroup parent)
    {
        ViewHolder holder;
        View view = convertView;
        int type;

        if (view == null)
        {
            holder = new ViewHolder();

            view = activity.LayoutInflater.Inflate(Resource.Layout.hospital_list_item, parent, false);
            holder.hospitalName = view.FindViewById<TextView>(Resource.Id.selectHospital_HospitalText);
            holder.hospitalFavourites = view.FindViewById<ToggleButton>(Resource.Id.selectHospital_FavouritesToggle);
            System.Diagnostics.Debug.WriteLine(holder.position);

            view.Click += delegate(object sender, EventArgs e)
            {
                var senderView = sender as View;
                if (senderView != null)
                {
                    var senderHolder = senderView.Tag as ViewHolder;
                    if (senderHolder != null)
                    {
                        Toast.MakeText(activity, senderHolder.position.ToString(), ToastLength.Short).Show();
                    }
                }
            };

            holder.hospitalFavourites.Click += delegate (object sender, EventArgs e)
            {
                var senderView = sender as View;
                if (senderView != null)
                {
                    var rowHolder = ((View)senderView.Parent).Tag as ViewHolder;
                    rowHolder.hospitalFavourites.Text = rowHolder.position.ToString();
                };
            };

            view.Tag = holder;
        }
        else
        {
            holder = view.Tag as ViewHolder;
        }

        //  Set height of row
        view.LayoutParameters.Height = 200;

        //  Set alternating background of row
        type = GetItemViewType(position);

        if (type == 0)
        {
            //view.SetBackgroundResource(Resource.Color._8_white);
            view.SetBackgroundColor(Android.Graphics.Color.AliceBlue);
        }

        //  Row contents
        holder.position = position;
        holder.hospitalName.Text = nameTexts[position];

        holder.hospitalFavourites.Text = position.ToString();
        holder.hospitalFavourites.SetOnCheckedChangeListener(null);

        return view;
    }

    //  Number of different rows
    public override int ViewTypeCount
    {
        get
        {
            return 2;
        }
    }

    //  To alternate rows
    public override int GetItemViewType(int position)
    {
        return position % 2 == 1 ? 0 : 1;
    }

    private readonly string[] nameTexts =
    {
    "Hospital 1",
    "Hospital 2",
    "Hospital 3",
    "Hospital 4",
    "Hospital 5",
    "Hospital 6",
    "Hospital 7",
    "Hospital 8",
    "Hospital 9",
    "Hospital 10",
    "Hospital 11",
    "Hospital 12",
    "Hospital 13",
    "Hospital 14",
    "Hospital 15",
    "Hospital 16",
    "Hospital 17",
    "Hospital 18",
    "Hospital 19",
    "Hospital 20",
    "Hospital 21",
    "Hospital 22",
    "Hospital 23",
    "Hospital 24",
    "Hospital 25"
};
}

class ViewHolder : Java.Lang.Object
{
    public TextView hospitalName { get; set; }
    public ToggleButton hospitalFavourites { get; set; }
    public int position { get; set; }
}

}

Answer 3

它可能是适配器中的委托，有时可能是许多问题的根源。尝试使用方法委托而不是匿名委托。并在正确设置之前将 onclick 事件设置为 null。

这是因为对象正在被回收，并且 click 方法可以调用两次，因此您不需要 if(view == null)。

我希望你能理解我，我无法提供经过验证的示例代码，但它应该看起来像：

.
.
.
view.Click -= customOnClickMethod;
view.Click += customOnClickMethod;
.
.
.
void customOnClickMethod(object sender, EventArgs e){
    //implement onclick function

}

希望这会有所帮助。

Answer 4

设法用以下代码解决它：

class RecyclerViewAdapter_SelectHospital : RecyclerView.Adapter
{
    private readonly Context context;
    private List<Hospital> list;
    public event EventHandler<int> ItemClick;

    public RecyclerViewAdapter_SelectHospital(Context c, List<Hospital> l)
    {
        context = c;
        list = l;
    }

    public override int ItemCount
    {
        get
        {
            return list.Count;
        }
    }

    private void OnClick(int position)
    {
        ItemClick?.Invoke(this, position);
    }

    private void OnItemClick(object sender, int position)
    {
        if (list[position].favourited == false)
        {
            list[position].favourited = true;
        }
        else
        {
            list[position].favourited = false;
        }
    }

    public override long GetItemId(int position)
    {
        return position;
    }

    public override int GetItemViewType(int position)
    {
        return position % 2 == 1 ? 0 : 1;
    }

    public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
    {
        SelectHospital_ViewHolder vh = holder as SelectHospital_ViewHolder;

        //  Set height of row
        vh.ItemView.LayoutParameters.Height = Select_Hospital.LIST_HEIGHT / 6;

        //  Set alternating background of row
        int type = GetItemViewType(position);

        if (type == 0)
        {
            vh.ItemView.SetBackgroundResource(Resource.Color._8_white);
        }

        vh.hospitalName.Text = list[position].name;
        vh.hospitalFavourites.Checked = list[position].favourited;
    }

    public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
    {
        View view = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.sublayout_Hospital_List_Item, parent, false);
        SelectHospital_ViewHolder holder = new SelectHospital_ViewHolder(view, OnClick);

        holder.ItemView.Click += delegate
        {
            Intent intent = new Intent(context, typeof(Request_Appointment));
            intent.PutExtra("hospitalName", holder.hospitalName.Text);
            context.StartActivity(intent);
        };

        ItemClick -= OnItemClick;
        ItemClick += OnItemClick;

        return holder;
    }
}

class SelectHospital_ViewHolder : RecyclerView.ViewHolder
{
    public TextView hospitalName { get; set; }
    public ToggleButton hospitalFavourites { get; set; }

    public SelectHospital_ViewHolder(View view, Action<int> listener) : base(view)
    {
        hospitalName = view.FindViewById<TextView>(Resource.Id.selectHospital_HospitalText);
        hospitalFavourites = view.FindViewById<ToggleButton>(Resource.Id.selectHospital_FavouritesToggle);

        hospitalFavourites.Click += (sender, e) => listener(AdapterPosition);
    }
}