Expand CircleImage with Command

I would like to extend CircleImage (by James Montemagno) with a Command. I know I could use the TapGestureRecognizer, but then the CircleImage will not be disabled if the Command.CanExecute = False.
I've created a control that derives from CircleImage. The binding does not work! How do I set IsEnabled if CanExecute has changed?

public class CircleImageButton : CircleImage
{
    public CircleImageButton()
    {
        var tgr = new TapGestureRecognizer();
        tgr.SetBinding(TapGestureRecognizer.CommandProperty, new Binding("Command"));
        tgr.SetBinding(TapGestureRecognizer.CommandParameterProperty, new Binding("CommandParameter"));
        this.GestureRecognizers.Add(tgr);
    }

    #region Command

    /// <summary>The <see cref="Command"/> bindable property's name.</summary>
    public const string CommandPropertyName = "Command";

    /// <summary>Identifies the <see cref="Command"/> bindable property.</summary>
    public static readonly BindableProperty CommandProperty = BindableProperty.Create(
        CommandPropertyName, typeof(ICommand), typeof(CircleImageButton), default(ICommand), propertyChanged: CommandChanged);

    private static void CommandChanged(BindableObject bindable, object oldvalue, object newvalue)
    {

    }

    /// <summary>Gets or sets the value of the <see cref="Command"/> property.</summary>
    public ICommand Command
    {
        get => (ICommand)GetValue(CommandProperty);
        set => SetValue(CommandProperty, value);
    }

    #endregion

    #region CommandParameter

    /// <summary>The <see cref="CommandParameter"/> bindable property's name.</summary>
    public const string CommandParameterPropertyName = "CommandParameter";

    /// <summary>Identifies the <see cref="CommandParameter"/> bindable property.</summary>
    public static readonly BindableProperty CommandParameterProperty = BindableProperty.Create(
        CommandParameterPropertyName, typeof(object), typeof(CircleImageButton), default(object));

    /// <summary>Gets or sets the value of the <see cref="CommandParameter"/> property.</summary>
    public object CommandParameter
    {
        get => (object)GetValue(CommandParameterProperty);
        set => SetValue(CommandParameterProperty, value);
    }

    #endregion
}