Xamarin.Forms ImageButton

ImageButton.cs

using System.Windows.Input;
using Xamarin.Forms;

namespace xxx.Controls
{
    class ImageButton : Image
    {
        public static readonly BindableProperty CommandProperty
            = BindableProperty.Create(
                nameof(Command), typeof(ICommand), typeof(ImageButton),　null,
                propertyChanged: (b, o, n) => ((ImageButton)b).Command = (ICommand)n
            );

        public static readonly BindableProperty CommandParameterProperty
            = BindableProperty.Create(
                nameof(CommandParameter), typeof(object), typeof(ImageButton), null,
                propertyChanged: (b, o, n) => ((ImageButton)b).CommandParameter = n
            );

        public ICommand Command {
            get { return (ICommand)GetValue(CommandProperty); }
            set { SetValue(CommandProperty, value); }
        }

        public object CommandParameter {
            get { return GetValue(CommandParameterProperty); }
            set { SetValue(CommandParameterProperty, value); }
        }

        public ImageButton()
        {
            var gr = new TapGestureRecognizer();
            gr.Tapped += (s, e) => {
                this.Command?.Execute(this.CommandParameter);
            };
            this.GestureRecognizers.Add(gr);
        }
    }
}

これと組み合わせて使うと便利。
※PCLに埋め込みリソースとして追加した画像を XAML から使う方法 (Markup Extension)
https://gist.github.com/conceptdev/d906c4538a137932fcf6