<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:WeChatPayDemo"
             x:Class="WeChatPayDemo.MainPage">

    <StackLayout>
        <WebView x:Name="wb" IsVisible="True" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
            
        </WebView>
    </StackLayout>

</ContentPage>

  public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();
            wb.Source = new UrlWebViewSource
            {
                Url = "http://wxpay.wxutil.com/mch/pay/h5.v2.php"
            };

        }

    }

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Webkit;
using Android.Widget;
using Xamarin.Forms;
using Xamarin.Forms.Internals;
using Xamarin.Forms.Platform.Android;
using AWebView = Android.Webkit.WebView;
[assembly: Xamarin.Forms.ExportRenderer(typeof(Xamarin.Forms.WebView), typeof(WeChatPayDemo.Droid.WebRenderer))]
namespace WeChatPayDemo.Droid
{
    public class WebRenderer : ViewRenderer<Xamarin.Forms.WebView, AWebView>
    {
        Context _context;

        public WebRenderer(Context context) : base(context)
        {
            _context = context;
        }

        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.WebView> e)
        {
            base.OnElementChanged(e);

            if (Control == null)
            {
                var webView = new AWebView(_context);
                webView.SetWebViewClient(new WebViewClient(_context));
                webView.Settings.JavaScriptEnabled = true;
                SetNativeControl(webView);
            }
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);
            if (Control != null && e.PropertyName == "Source")
            {
                var src = Element.Source as UrlWebViewSource;
                Control.LoadUrl(src.Url);
            }
        }
    }

    public class WebViewClient : Android.Webkit.WebViewClient
    {
        private Context _context;
        public WebViewClient(Context context)
        {
            _context = context;
        }
        public override bool ShouldOverrideUrlLoading(AWebView view, IWebResourceRequest request)
        {
            if (request.Url.Scheme == "weixin")
            {
                Intent intent = new Intent() { };
                intent.SetAction(Intent.ActionView);
                intent.SetData(request.Url);
                this._context.StartActivity(intent);
                return true;
            }
            return base.ShouldOverrideUrlLoading(view, request);
        }

        [Obsolete]
        public override bool ShouldOverrideUrlLoading(AWebView view, string url)
        {
            if (url.StartsWith("weixin"))
            {
                Intent intent = new Intent() { };
                intent.SetAction(Intent.ActionView);
                intent.SetData(Android.Net.Uri.Parse(url));
                this._context.StartActivity(intent);
                return true;
            }
            return base.ShouldOverrideUrlLoading(view, url);
        }
    }

}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Foundation;
using UIKit;
using Xamarin.Forms.Platform.iOS;
[assembly: Xamarin.Forms.ExportRenderer(typeof(Xamarin.Forms.WebView), typeof(WeChatPayDemo.iOS.WebRenderer))]
namespace WeChatPayDemo.iOS
{
    public class WebRenderer : WebViewRenderer
    {
        protected override void OnElementChanged(VisualElementChangedEventArgs e)
        {
            base.OnElementChanged(e);

            if (NativeView != null && e.NewElement != null)
                SetupControlSettings();

        }

        private void SetupControlSettings()
        {
            var webView = ((UIWebView)NativeView);
            if (webView == null) return;
            webView.Delegate = new CustomWebDelegate();
        }
    }


    public class CustomWebDelegate : UIWebViewDelegate
    { 

        public override bool ShouldStartLoad(UIWebView webView, NSUrlRequest request, UIWebViewNavigationType navigationType)
        {
            if (request.Url.Scheme== "weixin")
            {
                UIApplication.SharedApplication.OpenUrl(request.Url);
            } 
            return true;
        }


        public override void LoadingFinished(UIWebView webView)
        {

        }
        public override void LoadFailed(UIWebView webView, NSError error)
        {

        }
    }
}