How to modify the user agent of WebView in Xamarin Forms?

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To modify the user agent of WebView in Xamarin Forms, you can set the UserAgent property of the WebView object. Here's an example:

using Xamarin.Forms;
using System;
using System.Threading.Tasks;

namespace MyApp
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();

            webView.Navigating += WebView_Navigating;
            webView.Source = "https://www.example.com";
        }

        private void WebView_Navigating(object sender, WebNavigatingEventArgs e)
        {
            // modify the UserAgent of the WebView
            var customUserAgent = "MyApp/" + AppInfo.VersionString;
            var webView = (WebView)sender;
            webView.EvaluateJavaScriptAsync($"navigator.userAgent = '{customUserAgent}'");

            // do something else
        }
    }
}

In this example, we set the UserAgent to a custom value when the WebView is navigating to a new page. The custom value includes the name and version of the app (using the AppInfo class from Xamarin.Essentials). You can modify the customUserAgent variable to include any other information you want to include in the user agent string.

Note that the EvaluateJavaScriptAsync method is used to execute a JavaScript expression that sets the navigator.userAgent property to the custom user agent string. This is necessary because the UserAgent property is read-only, so we can't simply set it directly.