[Xamarin form] Dropdown control

AppDelegate.cs

public void ShowSubviewAt(CGRect rect, UIView subView, Action didFinishAnimation)
        {
            UIView cover = new UIView();
            cover.Frame = new CGRect(0, 0, AppWindow.Bounds.Width, AppWindow.Bounds.Height);
            //cover.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight;
            //cover.Opaque = true;
            cover.BackgroundColor = UIColor.Clear;
            cover.AddGestureRecognizer(new UITapGestureRecognizer(() =>
            {

                cover.RemoveFromSuperview();
                if (subView != null)
                    subView.RemoveFromSuperview();

            }));
            AppWindow.AddSubview(cover);

            subView.Frame = new CGRect(rect.X, rect.Y, rect.Width, 0);
            UIView.Animate(0.2, () =>
            {
                subView.Frame = new CGRect(rect.X, rect.Y, rect.Width, rect.Height);
                AppWindow.AddSubview(subView);
            }, didFinishAnimation);

        }

DropDownMenuRenderer_Android

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;

using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using App3.Droid.Views.Customs;

using App3.Views.Customs;
using App3.ViewModels;
using Android.Support.V4.View;
using System.ComponentModel;
using Java.Lang;

[assembly: ExportRenderer(typeof(DropDownMenuView), typeof(DropDownMenuRender_Android))]
namespace App3.Droid.Views.Customs
{
    public class DropDownMenuRender_Android : ViewRenderer<DropDownMenuView, Android.Views.View>, Spinner.IOnItemSelectedListener
    {
        Spinner _nativeView;
        Spinner.IOnItemSelectedListener _itemSelected;
        DropDownMenuView _dropDownView;
        SpinnerAdapter _adapter;

        protected override void OnElementChanged(ElementChangedEventArgs<DropDownMenuView> e)
        {
            base.OnElementChanged(e);
            if (e.NewElement != null)
            {
                _dropDownView = (DropDownMenuView)e.NewElement;

                if (Control == null)
                {
                    Android.Widget.RelativeLayout wraper = new Android.Widget.RelativeLayout(Android.App.Application.Context);
                    ContextThemeWrapper theme = new ContextThemeWrapper(Android.App.Application.Context, App3.Droid.Resource.Style.SpinnerAsEditText);
                    _nativeView = new Spinner(theme);
                    _nativeView.OnItemSelectedListener = this;
                    if (Android.OS.Build.VERSION.SdkInt < Android.OS.BuildVersionCodes.M)
                        _nativeView.SetBackgroundResource(App3.Droid.Resource.Drawable.border);
                    else
                        wraper.SetBackgroundResource(App3.Droid.Resource.Drawable.border);
                    _nativeView.LayoutParameters = new Android.Widget.RelativeLayout.LayoutParams(LayoutParams.MatchParent, LayoutParams.MatchParent);
                    _dropDownView.SetItemSelection = (i) => {
                        _nativeView.SetSelection(i);
                    };

                    ImageView downIcon = new ImageView(Android.App.Application.Context);
                    var param = new Android.Widget.RelativeLayout.LayoutParams(20, 20);
                    param.AddRule(LayoutRules.AlignParentRight);
                    param.AddRule(LayoutRules.CenterInParent);
                    param.SetMargins(0, 0, 14, 0);
                    downIcon.LayoutParameters = param;
                    downIcon.SetImageResource(App3.Droid.Resource.Drawable.ic_arrow_drop_down_black);
                    
                    wraper.AddView(_nativeView);
                    wraper.AddView(downIcon);
                    SetNativeControl(wraper);
                }

                if (_dropDownView.ItemsSource != null)
                    SetApdater();
            }
        }

        private void SetApdater()
        {
            if(_dropDownView.ItemsSource!=null)
            {
                //ArrayAdapter<String> adapter = new ArrayAdapter<String>(Android.App.Application.Context,
                //        Android.Resource.Layout.SimpleSpinnerItem, _dropDownView.ItemsSource);
                //adapter.SetDropDownViewResource(Android.Resource.Layout.SimpleListItemSingleChoice);
                if (_adapter == null)
                {
                    _adapter = new SpinnerAdapter(_dropDownView.ItemsSource);
                    _nativeView.Adapter = _adapter;
                }
                else
                    _adapter.SetData(_dropDownView.ItemsSource);
            }
        }

        class SpinnerAdapter : BaseAdapter
        {
            private List<string> _datas;
            public SpinnerAdapter(List<string> datas)
            {
                _datas = datas;
            }

            public override int Count
            {
                get
                {
                    return _datas != null ? _datas.Count : 0;
                }
            }

            public void SetData(List<string> datas)
            {
                _datas = datas;
                NotifyDataSetChanged();
            }

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

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

            public override Android.Views.View GetView(int position, Android.Views.View convertView, ViewGroup parent)
            {
                var item = (Android.Views.View)Android.Views.View.Inflate(Android.App.Application.Context, Resource.Layout.spinner_item, null);
                TextView text = item.FindViewById<TextView>(App3.Droid.Resource.Id.txtSpinnerText1);
                text.Text = _datas[position];
                if (Android.OS.Build.VERSION.SdkInt < Android.OS.BuildVersionCodes.M)
                {
                    item.SetBackgroundResource(App3.Droid.Resource.Drawable.border);
                    item.FindViewById(App3.Droid.Resource.Id.line).Visibility = ViewStates.Gone;
                }
                return item;
            }
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);
            SetApdater();
        }

        public void OnItemSelected(AdapterView parent, Android.Views.View view, int position, long id)
        {
            if(_dropDownView.ItemSelecetedEvent!=null)
            {
                _dropDownView.ItemSelecetedEvent.Invoke(position);
            }
        }

        public void OnNothingSelected(AdapterView parent)
        {
            if (_dropDownView.ItemSelecetedEvent != null)
            {
                _dropDownView.ItemSelecetedEvent.Invoke(-1);
            }
        }
    }
}

DropDownMenuRenderer_IOS.cs

using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using App3.iOS.Views.Custom;
using App3.Views.Customs;
using System;
using UIKit;
using Foundation;
using CoreGraphics;

[assembly: ExportRenderer(typeof(DropDownMenuView), typeof(DropDownMenuRender_iOS))]

namespace App3.iOS.Views.Custom
{
    public class DropDownMenuRender_iOS : ViewRenderer<DropDownMenuView, UIView>
    {
        DropDownMenuView _dropDownView;
        UITableView tableView;
        UIView wrapper;
        UILabel label;
        UIImageView arrow;
        int selectedIndex = 0;

        protected override void OnElementChanged(ElementChangedEventArgs<DropDownMenuView> e)
        {
            base.OnElementChanged(e);
            if (e.NewElement != null)
            {
                _dropDownView = (DropDownMenuView)e.NewElement;
                if (Control == null)
                {
                    wrapper = new UIView();
                    wrapper.Layer.BorderColor = ColorExtensions.ToCGColor(Color.FromHex(Define.DISABLE_CONTENT_COLOR));
                    wrapper.Layer.BorderWidth = 1;
                    wrapper.Frame = this.Frame;
                    //wrapper.BackgroundColor = UIColor.Red;
                    wrapper.AddGestureRecognizer( new UITapGestureRecognizer(() =>{
                        ButtonClickHanlde();
                    }));

                    arrow = new UIImageView();
                    arrow.Image = new UIImage("ic_arrow_drop_down_black.png");
                        arrow.Frame = new CGRect(10, 10, 50, 30);
                    wrapper.AddSubview(arrow);


                    label = new UILabel();
                    label.TextColor = UIColor.Black;
                    label.Frame = new CGRect(10, 10, 50, 30);
                        if (_dropDownView != null && _dropDownView.ItemsSource != null)
                        label.Text = _dropDownView.ItemsSource[0];
                    wrapper.AddSubview(label);
                    tableView = new UITableView();
                    //tableView
                    tableView.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight;
                    tableView.Frame = wrapper.Frame;
                    tableView.Layer.BorderWidth = 1;
                    tableView.Layer.BorderColor = ColorExtensions.ToCGColor(Color.FromHex(Define.DISABLE_CONTENT_COLOR));
                    tableView.WeakDelegate = this;
                    tableView.WeakDataSource = this;
                    _dropDownView.SetItemSelection += (obj) => {
                        //if(label!=null)
                        selectedIndex = obj;
                        label.Text = _dropDownView.ItemsSource[obj];
                        if (_dropDownView.ItemSelecetedEvent != null)
                            _dropDownView.ItemSelecetedEvent.Invoke(obj);
                    };
                    SetNativeControl(wrapper);
                }
            }

        }

        protected override void Dispose(bool disposing)
        {
            if (disposing && tableView != null)
                tableView.RemoveFromSuperview();
        
            base.Dispose(disposing);
        }

        public override CGRect Frame
        {
            get
            {
                return base.Frame;
            }
            set
            {
                base.Frame = value;
                if  ( label!=null&& wrapper != null && value != CGRect.Empty)
                {
                    //label.BackgroundColor = UIColor.Green;
                    label.Frame = new CGRect(8, 2, value.Size.Width - 10, value.Size.Height - 4);
                    this.LayoutSubviews();

                }
                if (arrow != null && wrapper != null && value != CGRect.Empty)
                {
                    //arrow.BackgroundColor = UIColor.Green;
                    arrow.Frame = new CGRect(value.Size.Width-20, (value.Size.Height-10)/2, 10, 10);
                    this.LayoutSubviews();
                }


            }
        }

        public void UpdateButton(string name)
        {
            
        }

        bool isShowDialog = false;
        private void ButtonClickHanlde()
        {
            if (wrapper == null)
                return;
            isShowDialog = !isShowDialog;
            if(isShowDialog)
            {
                var rect = wrapper.ConvertRectToView(wrapper.Frame, AppDelegate.AppWindow);
                nfloat height = AppDelegate.AppWindow.Bounds.Height - rect.Y - 10; 
                CGRect r = new CGRect(rect.X, rect.Y, rect.Width, height);
                int listCount= _dropDownView == null ? 0 : _dropDownView.ItemsSource.Count;

                AppDelegate.Instance.ShowSubviewAt(r, tableView,()=>{
                    if (selectedIndex < listCount)
                        tableView.ScrollToRow(NSIndexPath.FromRowSection(selectedIndex, 0), UITableViewScrollPosition.Top, false);
                });
                
            }else
            {
                tableView.RemoveFromSuperview();
            }

        }

      
        [Export("tableView:numberOfRowsInSection:")]
        public nint RowsInSection(UITableView tableView, nint section)
        {
            return _dropDownView == null ? 0 : _dropDownView.ItemsSource.Count;
        }


        [Export("tableView:cellForRowAtIndexPath:")]
        public  UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
        {
            var simpleTableIdentifier = @"SimpleTableItem";

            var cell = tableView.DequeueReusableCell(simpleTableIdentifier);

            if (cell == null)

            {
                cell = new UITableViewCell(UITableViewCellStyle.Default, simpleTableIdentifier);
            }

            cell.TextLabel.Text = _dropDownView.ItemsSource[indexPath.Row];
            return cell;
        }

        [Export("numberOfSectionsInTableView:")]
        public virtual nint NumberOfSections(UITableView tableView)
        {
            return 1;
        }


        [Export("tableView:didSelectRowAtIndexPath:")]
        public void RowSelected(UITableView tableView, NSIndexPath indexPath)
        {
            selectedIndex = indexPath.Row;
            ButtonClickHanlde();
            tableView.DeselectRow(indexPath,true);
            label.Text = _dropDownView.ItemsSource[indexPath.Row];
            if (_dropDownView.ItemSelecetedEvent != null)
                _dropDownView.ItemSelecetedEvent.Invoke(indexPath.Row);
        }

        [Export("tableView:heightForRowAtIndexPath:")]
        public virtual nfloat GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
        {
            return 50;
        }

    }
}

DropDownMenuView.cs

using Xamarin.Forms;
using System.Collections.Generic;
namespace Demo.Views.Customs
{
    public class DropDownMenuView : View
    {
        public static readonly BindableProperty ItemsSourceProperty = BindableProperty.Create("ItemsSource", typeof(List<string>), typeof(DropDownMenuView));
        public static readonly BindableProperty ItemSelecetedEventProperty = BindableProperty.Create("ItemSelecetedEvent", typeof(Action<int>), typeof(DropDownMenuView));
        public static readonly BindableProperty SetItemSelectionProperty = BindableProperty.Create("SetItemSelection", typeof(Action<int>), typeof(DropDownMenuView));

        public List<string> ItemsSource
        {
            get { return (List<string>)GetValue(ItemsSourceProperty); }
            set { SetValue(ItemsSourceProperty, value); }
        }

        public Action<int> ItemSelecetedEvent
        {
            get { return (Action<int>)GetValue(ItemSelecetedEventProperty); }
            set { SetValue(ItemSelecetedEventProperty, value); }
        }
          public Action<int> SetItemSelection
        {
            get { return (Action<int>)GetValue(SetItemSelectionProperty); }
            set { SetValue(SetItemSelectionProperty, value); }
        }
    }
}