FabSampleForms.Shared.MainPage.cs

public class MainPage : ContentPage
{
    public MainPage()
    {
        var fab = new FloatingActionButtonView() {
            ImageName = "ic_add.png",
            ColorNormal = Color.FromHex("ff3498db"),
            ColorPressed = Color.Black,
            ColorRipple = Color.FromHex("ff3498db")
        };

        // Main page layout
        var pageLayout = new StackLayout {
            Children = 
            {
                new Label {
                    VerticalOptions = LayoutOptions.CenterAndExpand,
                    XAlign = TextAlignment.Center,
                    Text = "Welcome to Xamarin Forms!" 
                }
            }};

        var absolute = new AbsoluteLayout() { 
            VerticalOptions = LayoutOptions.FillAndExpand, 
            HorizontalOptions = LayoutOptions.FillAndExpand };

        // Position the pageLayout to fill the entire screen.
        // Manage positioning of child elements on the page by editing the pageLayout.
        AbsoluteLayout.SetLayoutFlags(pageLayout, AbsoluteLayoutFlags.All);
        AbsoluteLayout.SetLayoutBounds(pageLayout, new Rectangle(0f, 0f, 1f, 1f));
        absolute.Children.Add(pageLayout);

        // Overlay the FAB in the bottom-right corner
        AbsoluteLayout.SetLayoutFlags(fab, AbsoluteLayoutFlags.PositionProportional);
        AbsoluteLayout.SetLayoutBounds(fab, new Rectangle(1f, 1f, AbsoluteLayout.AutoSize, AbsoluteLayout.AutoSize));
        absolute.Children.Add(fab);

        Content = absolute;
    }
}