您可以使用将影响所有条目的自定义渲染器，

you can use custom renderer that will affect all entries,

适用于安卓:

[assembly: ExportRenderer(typeof(Entry), typeof(MyEntryRenderer))]
namespace Android.MyRenderers
{
    public class MyEntryRenderer : EntryRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
        {
            base.OnElementChanged(e);

            if (Control == null || e.NewElement == null) return;

            if (Build.VERSION.SdkInt >= BuildVersionCodes.Lollipop)
                Control.BackgroundTintList = ColorStateList.ValueOf(Color.White);
            else
                Control.Background.SetColorFilter(Color.White, PorterDuff.Mode.SrcAtop);
         }    
    }
}

和 iOS:

[assembly: ExportRenderer (typeof(Entry), typeof(MyEntryRenderer))]
namespace iOS.MyRenderers
{
    public class MyEntryRenderer : EntryRenderer
    {
        private CALayer _line;

        protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
        {
            base.OnElementChanged (e);
            _line = null;

            if (Control == null || e.NewElement == null)
                return;

            Control.BorderStyle = UITextBorderStyle.None;

            _line = new CALayer {
                BorderColor = UIColor.FromRGB(174, 174, 174).CGColor,
                BackgroundColor = UIColor.FromRGB(174, 174, 174).CGColor,
                Frame = new CGRect (0, Frame.Height / 2, Frame.Width * 2, 1f)
            };

            Control.Layer.AddSublayer (_line);
        }
    }
}

不确定有关此的 Windows 解决方案

not sure about Windows solution on this