Binding in a Custom ViewCell

I have a custom ViewCell which I want to use in a TableView:

    public partial class InputCell : ViewCell
    {
        public static readonly BindableProperty LabelProperty = BindableProperty.Create("Label", typeof(string), typeof(InputCell));
        public static readonly BindableProperty TextProperty = BindableProperty.Create("Text", typeof(string), typeof(InputCell));

        public string Label
        {
            get { return (string)GetValue(LabelProperty); }
            set { SetValue(LabelProperty, value); }
        }

        public string Text
        {
            get { return (string)GetValue(TextProperty); }
            set { SetValue(TextProperty, value); }
        }

        public InputCell()
        {
            InitializeComponent();
            BindingContext = this;
        }
    }

I use it in my XAML-File like this:

            <TableView>
                <TableRoot>
                    <TableSection>
                        <local:InputCell x:Name="IcServer" Label="Server" Text="{Binding Server}"/>

Unfortunately the Binding does not work. I can only show Data when I use Code behind Forms like:

IcServer.Text = _preferences.Server;

The ViewModel and all my Properties are working well, I tested them with simple Labels on my Form. I can type in Data via Keyboard and everything works well, only after I bound the BindingContext to my ViewModel (_preferences) the Form shows no Data.

What am I missing ?