如何在xamarin表单中自定义ZXingDefaultOverlay

public class CustomOverlayView : ContentView
{
    public CustomOverlayView()
    {
        // 创建扫描框
        var scanBox = new BoxView
        {
            Color = Color.Black.MultiplyAlpha(0.5),
            CornerRadius = 10,
            HorizontalOptions = LayoutOptions.Center,
            VerticalOptions = LayoutOptions.Center,
            WidthRequest = 300,
            HeightRequest = 300
        };

        // 添加定位点
        var topLeftDot = new BoxView { Color = Color.White, WidthRequest = 20, HeightRequest = 20 };
        var topRightDot = new BoxView { Color = Color.White, WidthRequest = 20, HeightRequest = 20 };
        var bottomLeftDot = new BoxView { Color = Color.White, WidthRequest = 20, HeightRequest = 20 };
        var bottomRightDot = new BoxView { Color = Color.White, WidthRequest = 20, HeightRequest = 20 };

        // 布局定位点
        // ...

        // 将元素添加到布局中
        var layout = new AbsoluteLayout();
        AbsoluteLayout.SetLayoutFlags(scanBox, AbsoluteLayoutFlags.All);
        AbsoluteLayout.SetLayoutBounds(scanBox, new Rectangle(0.5, 0.5, 0.8, 0.8));
        layout.Children.Add(scanBox);

        // 添加其他元素...

        Content = layout;
    }
}

public class ScanPage : ContentPage
{
    public ScanPage()
    {
        var scanner = new ZXingScannerView();
        var overlay = new CustomOverlayView();

        // 将扫描器和覆盖层添加到布局中
        var layout = new AbsoluteLayout();
        AbsoluteLayout.SetLayoutFlags(scanner, AbsoluteLayoutFlags.All);
        AbsoluteLayout.SetLayoutBounds(scanner, new Rectangle(0, 0, 1, 1));
        layout.Children.Add(scanner);
        layout.Children.Add(overlay);

        Content = layout;
    }
}