Xamarin.Formsで背景画像を設定する方法

もしかしたら少し外してるかもしれませんが…。

namespace BackgroundTest
{
    public class TestApp : Xamarin.Forms.Application
    {
        public TestApp()
        {
            MainPage = new AppPage();
        }
    }

    public class AppPage : ContentPage
    {
        public AppPage()
        {
            var baseLayout = new Grid()
            {
                BackgroundColor = Color.FromRgb(0.7, 0.7, 1.0),
            };
            baseLayout.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
            baseLayout.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });

            baseLayout.Children.Add(new Image()
            {
                HorizontalOptions = LayoutOptions.FillAndExpand,
                VerticalOptions = LayoutOptions.FillAndExpand,
                Aspect = Aspect.AspectFit,
                Source = "387ada2dbf6a4a03c802a1cc478b5aa5.png",
            }, 0, 0);

            baseLayout.Children.Add(new StackLayout()
            {
                Orientation = StackOrientation.Vertical,
                Children =
                {
                    new Label()
                    {
                        HorizontalOptions = LayoutOptions.FillAndExpand,
                        VerticalOptions = LayoutOptions.FillAndExpand,
                        HorizontalTextAlignment = TextAlignment.Center,
                        VerticalTextAlignment = TextAlignment.Center,
                        Text = "Hello, world",
                    },
                }
            }, 0, 0);

            Content = baseLayout;
        }
    }
}

Gridをベースにして
・画像
・メインのコンテンツ
を張り付けてしまう、というやり方でどうでしょうか？

BackgroundImage プロパティは Page を継承したクラスにありそうです。

public App()
    {
      // The root page of your application
      var content = new ContentPage
      {
        Title = "background1201",
        BackgroundImage = "icon.png",
        Content = new StackLayout
        {
          VerticalOptions = LayoutOptions.Center,
          Children = {
            new Label {
              HorizontalTextAlignment = TextAlignment.Center,
              Text = "Welcome to Xamarin Forms!"
            }
          }
        }
      };

      MainPage = new NavigationPage(content);
    }