更正Xamarin frame ios的阴影

using Xamarin.Forms.Platform.iOS;

// ...

public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
    // ...

    Forms.Init();
    LoadApplication(new App());

    // Add customizations for Frame shadow
    var frameRenderer = new FrameRenderer();
    frameRenderer.ShadowOpacity = 0.8f;
    frameRenderer.ShadowRadius = 5;
    frameRenderer.ShadowColor = UIColor.Black.CGColor;
    frameRenderer.ShadowOffset = new CGSize(0, 2);
    Xamarin.Forms.FormsMaterial.Init();

    return base.FinishedLaunching(app, options);
}

var frame = new Frame
{
    Content = new Label { Text = "Hello Xamarin.Forms!" },
    Margin = new Thickness(20),
    Padding = new Thickness(10),
    BackgroundColor = Color.White,
    CornerRadius = 5
};

Content = new StackLayout
{
    Children = { frame }
};