I m making a Gallery Page using xamarin forms. I wrote the Code in Pure C# & it worked but when I try to do same in XAML following the MVVM, nothing appears on page,there is some binding issue with the image. Please Help.

C# Code

        public class GalleryPlus : ContentPage
        {
            const string keys = "**********************************";
            ObservableCollection<string> images = new ObservableCollection<string> ();
            ObservableCollection<ItemModel> List;

            ProgressBar pb;
            public bool boolVisible {
                get;
                set;
            }
            public bool boolRunning {
                get;
                set;
            }
            async Task<bool> AlphaPhase ()
            {
                RootObject rootobject = new RootObject ();
                var client = new System.Net.Http.HttpClient ();
                string Jsonstr = string.Format ("https://api.instagram.com/v1/users/self/media/recent?access_token={0}", keys);
                var response = await client.GetAsync (Jsonstr);
                var earthquakesJson = response.Content.ReadAsStringAsync ().Result;
                rootobject = JsonConvert.DeserializeObject<RootObject> (earthquakesJson);
                await pb.ProgressTo (.5, 250, Easing.Linear);
                foreach (var item in rootobject.data) {
                    images.Add (item.images.low_resolution.url);
                }
                if (images.Count > 0) {
                    await pb.ProgressTo (.6, 250, Easing.Linear);
                    return true;
                } else {
                    await pb.ProgressTo (.99, 250, Easing.Linear);
                    return false;
                }
            }
            async void BetaPhase ()
            {
                await pb.ProgressTo (.4, 250, Easing.Linear);
                var result = await AlphaPhase ();
                if (result.Equals (true)) {
                    int number = 0;
                    //  for (int n = 0; n < 20; n++) {
                    for (int i = 0; i < images.Count; i++) {
                        number++;
                        var item = new ItemModel () {
                            ImageUrl = images [i],
                            FileName = string.Format ("image_{0}.jpg", number),
                        };

                        List.Add (item);
                        //  }
                    }
                    await pb.ProgressTo (.7, 250, Easing.Linear);
                }
            }
            public GalleryPlus ()
            {
                List = new ObservableCollection<ItemModel> ();
                Image imge = new Image { Source = "gallery_iamge.png", Aspect = Aspect.AspectFill };
                pb = new ProgressBar { IsVisible = true, IsEnabled = true, Progress = .2 };
                FlowListView listView = new FlowListView () {
                    FlowColumnTemplate = new DataTemplate (typeof (ListCell)),
                    SeparatorVisibility = SeparatorVisibility.None,
                    HasUnevenRows = true,
                    FlowColumnMinWidth = 110,
                    FlowItemsSource = List,
                };
                listView.FlowItemTapped += (s, e) => {
                    var item = (ItemModel)e.Item;
                    if (item != null) {
                        App.Current.MainPage.DisplayAlert ("Alert", "Tapped {0} =" + item.FileName, "Cancel");
                    }
                };

                Content = new StackLayout {
                    Children = {

                        imge,
                        pb,
                       listView
                    }
                };
                BetaPhase ();


            }
            public class ItemModel
            {
                public string ImageUrl { get; set; }
                public string FileName { get; set; }

            }
            public class ListCell : ContentView
            {
                public ListCell ()
                {
                    CachedImage IconImage = new CachedImage {
                        HeightRequest = 100,
                        Aspect = Aspect.Fill,
                        DownsampleHeight = 100,
                        DownsampleUseDipUnits = false,
                    };
                    IconImage.SetBinding (CachedImage.SourceProperty, "ImageUrl");
                    Grid grd = new Grid {
                        Padding = 3,
                        ColumnDefinitions = {
                        new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) },
                    },
                        RowDefinitions = {
                        new RowDefinition { Height=GridLength.Star},
                    },
                    };
                    grd.Children.Add (IconImage, 0, 0);
                    Content = grd;
                }
            }
        }}

XAML CODE

             <?xml version="1.0" encoding="UTF-8"?>
            <ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
        Title="GALLERY" x:Class="BarberShop.Gallery" 
        xmlns:flv="clr-namespace:DLToolkit.Forms.Controls;assembly=DLToolkit.Forms.Controls.FlowListView" 
        xmlns:ffimageloading="clr-namespace:FFImageLoading.Forms;assembly=FFImageLoading.Forms">
            <ContentPage.Content>
            <StackLayout>
            <Image Aspect="AspectFill" Source="gallery_iamge.png" />

            <flv:FlowListView SeparatorVisibility="None" HasUnevenRows="true" FlowItemTappedCommand="{Binding TapCommand}" FlowColumnMinWidth="110" FlowItemsSource="{Binding List}">
            <flv:FlowListView.FlowColumnTemplate>
            <DataTemplate>
            <Grid Padding="3">
            <Grid.RowDefinitions>
            <RowDefinition Height="100" />
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>
            <ffimageloading:CachedImage HeightRequest="100" Aspect="AspectFill" DownsampleHeight="100" DownsampleUseDipUnits="false" Source="{Binding ImageUrl}" />
            </Grid>
            </DataTemplate>
            </flv:FlowListView.FlowColumnTemplate>
            </flv:FlowListView>


                </StackLayout>
            </ContentPage.Content>
        </ContentPage>

ViewModelCode

    public class GalleryViewModel : ViewModelBase
        {
            public class ItemModel
            {
                public string ImageUrl { get; set; }
                public string FileName { get; set; }

            }
    const string keys = "******************";

            ObservableCollection<ItemModel> List { get; set; }
    public GalleryViewModel ()
            {
    List = new ObservableCollection<ItemModel> ();
                BetaPhase ();
    }



            async Task<bool> AlphaPhase ()
            {

                RootObject rootobject = new RootObject ();
                var client = new System.Net.Http.HttpClient ();
                string Jsonstr = string.Format ("https://api.instagram.com/v1/users/self/media/recent?access_token={0}", keys);
                var response = await client.GetAsync (Jsonstr);
                var earthquakesJson = response.Content.ReadAsStringAsync ().Result;
                rootobject = JsonConvert.DeserializeObject<RootObject> (earthquakesJson);
                foreach (var item in rootobject.data) {
                    images.Add (item.images.low_resolution.url);
                }
                response.Dispose ();

                if (images.Count > 0) {
                    return true;
                } else {
                    return false;
                }
            }

            async void BetaPhase ()
            {

                var result = await AlphaPhase ();
                if (result.Equals (true)) {
                    int number = 0;
                    for (int n = 0; n < 20; n++) {
                        for (int i = 0; i < images.Count; i++) {
                            number++;
                            var item = new ItemModel () {
                                ImageUrl = images [i],
                                FileName = string.Format ("image_{0}.jpg", number),
                            };


                            List.Add (item);
                        }
                    }

                }
            }