C# — Simple rounded avatar class example for Xamarin.Forms

Avatar.cs

//
//  Avatar.cs
//  Created by Alexey Kinev on 26 Feb 2015.
//
//    Licensed under The MIT License (MIT)
//    http://opensource.org/licenses/MIT
//
// Simple rounded avatar class example for Xamarin.Forms.
//
using System;
using Xamarin.Forms;
using ImageCircle.Forms.Plugin.Abstractions;

namespace Project
{
    public class Avatar : AbsoluteLayout
    {
        /// <summary>
        /// The image URI property.
        /// </summary>
        public static readonly BindableProperty ImageUriProperty =
            BindableProperty.Create("ImageUri", typeof(String), typeof(Avatar), "");

        /// <summary>
        /// The circle background color property.
        /// </summary>
        public static readonly BindableProperty CircleBackgroundColorProperty =
            BindableProperty.Create("CircleBackgroundColor", typeof(Color), typeof(Avatar), Color.Default);

        /// <summary>
        /// The name property.
        /// </summary>
        public static readonly BindableProperty NameProperty =
            BindableProperty.Create("Name", typeof(String), typeof(Avatar), "");

        /// <summary>
        /// Gets or sets the image URI.
        /// </summary>
        public string ImageUri
        {
            get { return (string)GetValue(ImageUriProperty); }
            set { SetValue(ImageUriProperty, value); }
        }

        /// <summary>
        /// Gets or sets the color of the circle background.
        /// </summary>
        /// <value>The color of the circle background.</value>
        public Color CircleBackgroundColor
        {
            get { return (Color)GetValue(CircleBackgroundColorProperty); }
            set { SetValue(CircleBackgroundColorProperty, value); }
        }


        /// <summary>
        /// The default avatar image.
        /// </summary>
        static ImageSource GetDefaultImageSource()
        {
            if (defaultImage == null)
            {
                defaultImage = ImageSource.FromFile("default-avatar.png");
            }
            return defaultImage;
        }
        static ImageSource defaultImage;

        /// <summary>
        /// Gets or sets the name.
        /// </summary>
        public string Name
        {
            get { return (string)GetValue(NameProperty); }
            set { SetValue(NameProperty, value); }
        }

        /// <summary>
        /// The circle.
        /// </summary>
        readonly RoundedBox circle;

        /// <summary>
        /// The image.
        /// </summary>
        readonly CircleImage image;

        /// <summary>
        /// The name label.
        /// </summary>
        readonly Label nameLabel;

        /// <summary>
        /// Initializes a new instance of the <see cref="Project.Avatar"/> class.
        /// </summary>
        public Avatar()
        {
            // Circle
            circle = new Circle {
                BindingContext = this
            };
            circle.SetBinding(BackgroundColorProperty, "CircleBackgroundColor");
            circle.SetBinding(IsVisibleProperty, "ImageUri",
                converter: IsEmptyConverter.Instance); // show circle if image IS empty
            Children.Add(circle, new Rectangle(0.0, 0.0, 1.0, 1.0), AbsoluteLayoutFlags.All);

            // Name
            nameLabel = new Label {
                TextColor = Theme.LightTextColor,
                XAlign = TextAlignment.Center,
                YAlign = TextAlignment.Center,
                FontSize = Theme.LargeFontSize,
                BindingContext = this
            };
            nameLabel.SetBinding(Label.TextProperty, "Name",
                converter: NameToInitialsConverter.Instance);
            Children.Add(nameLabel, new Rectangle(0, 0, 1.0, 1.0), AbsoluteLayoutFlags.All);

            // Image
            image = new CircleImage {
                BorderThickness = 0,
                HorizontalOptions = LayoutOptions.Center,
                Aspect = Aspect.AspectFill,
                BackgroundColor = Color.Transparent,
                BindingContext = this
            };

            // We need intermediate cache layer here
            image.SetBinding(Image.SourceProperty, "ImageUri",
                converter: ImageSourceCachedConverter.Instance);

            // WOW!!! Pre-loading image to static data makes ListView scrolling become smooth!!!
            // image.Source = GetDefaultImageSource();

            // This works not as expected! Image is loaded, but seems like not cached on
            // per-name basis and is reloaded every time or something like that.
            // image.Source = ImageSource.FromFile("default-avatar.png");

            Children.Add(image, new Rectangle(0, 0, 1.0, 1.0), AbsoluteLayoutFlags.All);
        }
    }
}

ImageSourceCachedConverter.cs

//
//  ImageSourceCachedConverter.cs
//  Created by Alexey Kinev on 26 Feb 2015.
//
//    Licensed under The MIT License (MIT)
//    http://opensource.org/licenses/MIT
//
// Xamarin.Forms value converter for binding image sources by remote
// URIs with basic in-memory cache.
//
using System;
using System.Collections.Concurrent;
using Xamarin.Forms;

namespace Project
{
    using CacheDictionary = ConcurrentDictionary<string, ImageSource>;

    public class ImageSourceCachedConverter : IValueConverter
    {
        /// <summary>
        /// The instance of converter.
        /// </summary>
        public static readonly ImageSourceCachedConverter Instance =
            new ImageSourceCachedConverter();

        /// <summary>
        /// The cache.
        /// </summary>
        CacheDictionary cache;

        /// <summary>
        /// Initializes a new instance of the <see cref="Project.ImageSourceCachedConverter"/> class.
        /// </summary>
        ImageSourceCachedConverter()
        {
            cache = new CacheDictionary();
        }

        #region IValueConverter implementation

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            var source = value as string;

            if (!String.IsNullOrEmpty(source))
            {
                return cache.GetOrAdd(source, (imageUri) =>
                    ImageSource.FromUri(new Uri(imageUri)));
            }

            return null;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }

        #endregion
    }
}