Why is Xamarin.Android RecyclerView.Adapter not generic? - xamarin

Question

I have noticed the RecyclerView.Adapter type is not generic in Xamarin.Android. Why is it so? It seems to be defined as generic in native Android according to the documentation. Is there an underlying reason for this? Or is it some kind of backward compatiblity scenario?

Answer 1

You can create generic RecycleView in C# but not in java. In java you need to write code multiple times. That's why java android is worse even just simple event handler, Android Team Engineers are lazy to implements all data event handling because of the nature of java.
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Support.V7.Widget;
using Android.Util;
using Android.Views;
using Android.Widget;
namespace XamarinAndroid.Basic.Core
{
public class GenericRecyclerViewAdapter<T> : RecyclerView.Adapter
{
/// <summary>
/// You can set this for different custom cardview
/// </summary>
public int CardViewResourceLayout { get; set; }
public ObservableCollection<T> Items { get; private set; }
public event EventHandler<RecyclerViewViewHolder> ItemViewTemplated;
public GenericRecyclerViewAdapter(IEnumerable<T> items, int cardViewResourceLayout) : base()
{
this.Items = new ObservableCollection<T>(items);
this.CardViewResourceLayout = cardViewResourceLayout;
this.Items.CollectionChanged += (sender, e) =>
{
try
{
this.NotifyDataSetChanged();
}
catch { }
};
}
public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
{
var itemView = LayoutInflater.From(parent.Context).Inflate(CardViewResourceLayout, parent, false);
#if DEBUG
Log.Info("GenericRecyclerViewAdapter - ", CardViewResourceLayout.ToString());
#endif
RecyclerViewViewHolder vh = new RecyclerViewViewHolder(itemView);
return vh;
}
public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
{
RecyclerViewViewHolder vh = holder as RecyclerViewViewHolder;
vh.ItemPosition = position;
vh.TemplateView.Tag = position;
vh.TemplateView.Click -= TemplateView_Click;
vh.TemplateView.Click += TemplateView_Click;
this.ItemViewTemplated?.Invoke(this, vh);
}
public event EventHandler<T> ItemClicked;
private void TemplateView_Click(object sender, EventArgs e)
{
var position = (int)((View)sender).Tag;
this.ItemClicked?.Invoke(this, this.Items[position]);
}
public override int ItemCount
{
get { return this.Items.Count; }
}
public override long GetItemId(int position)
{
return base.GetItemId(position);
}
}
public class RecyclerViewViewHolder : RecyclerView.ViewHolder
{
public View TemplateView { get; private set; }
public int ItemPosition { get; set; }
public RecyclerViewViewHolder(View itemView) : base(itemView)
{
// Locate and cache view references:
this.TemplateView = itemView;
}
}
}
Assigning data to each view
var recyclerViewToday = this.FindViewById<Android.Support.V7.Widget.RecyclerView>(Resource.Id.recyclerViewToday);
var layoutManager = new LinearLayoutManager(this);
recyclerViewToday.SetLayoutManager(layoutManager);
var adapter = new GenericRecyclerViewAdapter<FavoriteModel>(previousList, Resource.Layout.recent_list_item);
adapter.ItemViewTemplated += (d, holder) =>
{
var indicate = holder.ItemView.FindViewById<View>(Resource.Id.indicatorItemmRec);
indicate.SetBackgroundColor(ColorHelper.GetRandomLightColor());
(holder.ItemView.FindViewById<TextView>(Resource.Id.wordTxtRec)).Text = adapter.Items[holder.ItemPosition].Word;
var textView = (holder.ItemView.FindViewById<TextView>(Resource.Id.definitionTxtRec));
if (!string.IsNullOrEmpty(previousList[holder.ItemPosition].Definition))
textView.Text = previousList[holder.ItemPosition].Definition;
else
textView.Visibility = Android.Views.ViewStates.Gone;
};
recyclerViewToday.SetAdapter(adapter);
Result

Answer 2

Clean, Generic and Reusable
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.Graphics;
using Android.OS;
using Android.Runtime;
using Android.Support.V7.App;
using Android.Support.V7.Widget;
using Android.Text;
using Android.Text.Style;
using Android.Util;
using Android.Views;
using Android.Widget;
using Java.Util.Zip;
using ActionMenuView = Android.Support.V7.Widget.ActionMenuView;
namespace Android.Basic.Core
{
public class GenericRecyclerViewAdapter<T> : RecyclerView.Adapter
{
/// <summary>
/// You can set this for different custom cardview
/// </summary>
private int CardViewResourceLayout { get; set; }
public ObservableCollection<T> Items { get; private set; }
public event EventHandler<RecyclerViewViewHolder> ItemViewTemplated;
public RecyclerView.LayoutManager layoutManager;
public GenericRecyclerViewAdapter(RecyclerView recyclerView, IEnumerable<T> items, int cardViewResourceLayout, bool isList = true, bool isVertical = true) : base()
{
if(isList)
{
var vertical = isVertical ? LinearLayoutManager.Vertical : LinearLayoutManager.Horizontal;
layoutManager = new LinearLayoutManager(recyclerView.Context, vertical, false);
}
else
{
var vertical = isVertical ? GridLayoutManager.Vertical : GridLayoutManager.Horizontal;
layoutManager = new GridLayoutManager(recyclerView.Context, 3, vertical, false);
}
recyclerView.SetLayoutManager(layoutManager);
this.Items = new ObservableCollection<T>(items);
this.CardViewResourceLayout = cardViewResourceLayout;
this.Items.CollectionChanged += delegate
{
this.NotifyDataSetChanged();
};
}
public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
{
var itemView = LayoutInflater.From(parent.Context).Inflate(CardViewResourceLayout, parent, false);
#if DEBUG
Log.Info("GenericRecyclerViewAdapter - ", CardViewResourceLayout.ToString());
#endif
RecyclerViewViewHolder vh = new RecyclerViewViewHolder(itemView);
return vh;
}
public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
{
RecyclerViewViewHolder vh = holder as RecyclerViewViewHolder;
vh.ItemPosition = position;
vh.TemplateView.Tag = position;
vh.TemplateView.Click -= TemplateView_Click;
vh.TemplateView.Click += TemplateView_Click;
ItemViewTemplated?.Invoke(this, vh);
}
public event EventHandler<T> ItemClicked;
private void TemplateView_Click(object sender, EventArgs e)
{
var position = (int)((View)sender).Tag;
this.ItemClicked?.Invoke(sender, this.Items[position]);
}
public override int ItemCount
{
get { return this.Items.Count; }
}
public override long GetItemId(int position)
{
return base.GetItemId(position);
}
}
public class RecyclerViewViewHolder : RecyclerView.ViewHolder, View.IOnCreateContextMenuListener,
IMenuItemOnMenuItemClickListener
{
public View TemplateView { get; private set; }
public int ItemPosition { get; set; }
public event EventHandler<MenuInfo> ContextMenuCreated;
public event EventHandler<object> MenuItemClicked;
public MenuInfo MenuInfo { get; private set; }
public object Data { get; set; }
public RecyclerViewViewHolder(View itemView) : base(itemView)
{
// Locate and cache view references:
this.TemplateView = itemView;
this.TemplateView.SetOnCreateContextMenuListener(this);
}
public void OnCreateContextMenu(IContextMenu menu, View v, IContextMenuContextMenuInfo menuInfo)
{
MenuInfo = new MenuInfo(menu, v, menuInfo);
ContextMenuCreated?.Invoke(this, MenuInfo);
}
private Android.Views.MenuInflater menuInflater = null;
/// <summary>
/// After ContextMenuCreated
/// </summary>
/// <param name="resourcemenu"></param>
public void InflateMenu(int resourcemenu, SpannableString titleColor = null, object dta = null)
{
if (dta != null)
this.Data = dta;
if (this.TemplateView.Context is AppCompatActivity activity)
{
menuInflater = activity.MenuInflater;
}
else if (this.TemplateView.Context is Activity activity2)
{
menuInflater = activity2.MenuInflater;
}
var contextMenu = this.MenuInfo.ContextMenu;
contextMenu.Clear();
menuInflater.Inflate(resourcemenu, contextMenu);
var num = contextMenu.Size() - 1;
for (int i = 0; i <= num; i++)
{
var men = contextMenu.GetItem(i);
if(titleColor != null)
{
if (i == 0)
{
men.SetTitle(titleColor);
men.SetChecked(true);
}
}
if (i != 0)
{
men.SetOnMenuItemClickListener(this);
}
}
}
public bool OnMenuItemClick(IMenuItem item)
{
this.MenuItemClicked?.Invoke(item, this.Data);
return true;
}
public float PosX;
public float PosY;
}
public class MenuInfo
{
public IContextMenu ContextMenu { get; }
public View View { get; }
public IContextMenuContextMenuInfo ContextMenuInfo { get; }
public MenuInfo(IContextMenu contextMenu, View view, IContextMenuContextMenuInfo menuInfo)
{
this.ContextMenu = contextMenu;
this.View = view;
this.ContextMenuInfo = menuInfo;
}
}
}
Usage
RecyclerView recyclerView = context.FindViewById<RecyclerView>(Resource.Id.recycler);
var viewAdapter = new Android.Basic.Core.GenericRecyclerViewAdapter<StorageFile>(recyclerView, files, Resource.Layout.main_item);
viewAdapter.ItemViewTemplated += (dd, holder) =>
{
//CardView
CardView cardView = holder.ItemView.FindViewById<CardView>(Resource.Id.CategorycardView);
cardView.SetCardBackgroundColor(ThemeHelper.IsDark ? Color.ParseColor("#303030") : Color.White);
var indicator = holder.ItemView.FindViewById<LinearLayout>(Resource.Id.indicator);
indicator.SetBackgroundColor(ThemeHelper.IsDark ? ColorHelper.GetRandomLightColor() : ColorHelper.GetRandomDarkColor());
var file = files[holder.ItemPosition];
var itemIcon = holder.ItemView.FindViewById<ImageView>(Resource.Id.itemIcon);
var icon = file.GetFileThumbnail();
if (icon != null)
{
itemIcon.SetImageBitmap(icon);
}
TextView itemName = holder.ItemView.FindViewById<TextView>(Resource.Id.itemName);
itemName.Text = file.DisplayName;
itemName.SetTextColor(textColor);
};
viewAdapter.ItemClicked += (dd, ff) =>
{
var checkBttn = (dd as View).FindViewById<ImageButton>(Resource.Id.check_boxBttn);
};
recyclerView.SetAdapter(viewAdapter);