如何在Xamarin.Forms中的网格中启用边框

我正在Xamarin.Forms中构建一个网格. 我想添加表格等边框. 我以为可以在定义行和列时添加边框，但是失败了. 谁能帮我? 这是我当前的代码.

I'm building a grid in Xamarin.Forms. And I'd like to add borders like tables. I thought that I could add the border when defining rows and columns, but failed. Can anyone help me? This is my current code.

Grid grid = new Grid {
    VerticalOptions = LayoutOptions.FillAndExpand,
    RowDefinitions = {
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },
        new RowDefinition { Height = GridLength.Auto },

    },
    ColumnDefinitions = {
        new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) },
        new ColumnDefinition { Width = new GridLength (5, GridUnitType.Star) },
        new ColumnDefinition { Width = new GridLength (1, GridUnitType.Star) },
    }
};