How to make the scroll bar visible always in xamarin forms in ios device and shift the scroll bar to left side of the screen?

Question

How to make the scroll bar always visible in Xamarin forms in IOS device and shift the scroll bar to left side of the screen?
I tried this link: Xamarin Forms ListView for iOS: Always Show ScrollBar

but getting exception that

Event registration is overwriting existing delegate. Either just use events or your own delegate: hupp.iOS.Models.CustomScrollDelegate UIKit.UIScrollView+_UIScrollViewDelegate

    public class CustomScrollViewRenderer : ScrollViewRenderer
{

    public UIView bar;

    protected override async void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);
       // UIScrollView iosScrollView = (UIScrollView)NativeView;

        this.ShowsVerticalScrollIndicator = ((CustomScrollViewLesson)e.NewElement).IsVerticalScrollbarEnabled;
        this.ShowsHorizontalScrollIndicator = ((CustomScrollViewLesson)e.NewElement).IsHorizontalScrollbarEnabled;

        this.IndicatorStyle = UIScrollViewIndicatorStyle.White;
        this.ScrollIndicatorInsets = new UIEdgeInsets(0, 30, 0, 30);
        this.FlashScrollIndicators();
        //Hide the default Scroll Indicator.
         this.ShowsVerticalScrollIndicator = false;
        //Set Delegate
        CustomScrollDelegate customScrollDelegate = new CustomScrollDelegate();
        this.Delegate = customScrollDelegate;


        //Create the background view of custom indicator.
        double frameHeight = this.Frame.Size.Height;
        double frameWidth = this.Frame.Size.Width;

        double barBackgroundWidth = 6;
        double statusBarHeight = 20; //this.ScrollIndicatorInsets = new UIEdgeInsets(0, 0, 0, this.Bounds.Size.Width - 10);
        UIView barBackgroundView = new UIView();
        CGRect barBVRect = new CGRect(frameWidth - barBackgroundWidth, statusBarHeight, barBackgroundWidth, frameHeight);
        barBackgroundView.Frame = barBVRect;
        barBackgroundView.BackgroundColor = UIColor.Gray;
        barBackgroundView.Layer.CornerRadius = 2;
        barBackgroundView.Layer.MasksToBounds = true;

        //Create the bar of the custom indicator.
        bar = new UIScrollView();
        CGRect barRect = new CGRect(1, 0, 4, 0);
        bar.Frame = barRect;
        bar.BackgroundColor = UIColor.White;
        bar.Layer.CornerRadius = 2;
        bar.Layer.MasksToBounds = true;

        //Add the views to the superview of the tableview.
        barBackgroundView.AddSubview(bar);
        this.Superview.AddSubview(barBackgroundView);//here also getting exception null value in superview.so i commented while debug
        customScrollDelegate.bar = bar;

        //Transfer the bar view to delegate.

    }

    public override void LayoutSubviews()
    {
        base.LayoutSubviews();
        Console.WriteLine("End of loading!!!");
        double contentHeight = this.ContentSize.Height;
        double frameHeight = this.Frame.Size.Height;
        double barHeight = frameHeight * frameHeight / contentHeight;


        //Reset the bar height when the table view finishes loading.
        CGRect barRect = new CGRect(bar.Frame.X, bar.Frame.Y, bar.Frame.Width, barHeight);
        bar.Frame = barRect;
    }
}
    public class CustomScrollDelegate : UIKit.UIScrollViewDelegate
{
    public UIView bar;
    double barY;

    public override void Scrolled(UIScrollView scrollView)
    {
        double y = scrollView.ContentOffset.Y;
        double contentHeight = scrollView.ContentSize.Height;
        double frameHeight = scrollView.Frame.Size.Height;

        double barHeight = frameHeight * frameHeight / contentHeight;
        barY = y / (contentHeight - frameHeight) * (frameHeight - barHeight);

        //Cut the bar Height when it over the top.
        if (barY < 0)
        {
            barHeight = barHeight + barY;
            barY = 0;
        }

        //Cut the bar height when it over the bottom.
        if (barY > (frameHeight - barHeight))
        {
            barHeight = barHeight - (barY - (frameHeight - barHeight));
        }

        //Reset the barView rect. Let's move!!!
        CGRect barRect = new CGRect(bar.Frame.X, barY, bar.Frame.Width, barHeight);
        bar.Frame = barRect;

    }

}     

Please give a solution and thanks in advance