为什么？

There is one important thing you have to understand about the nature
of an Unhandled exception in Android,there isn’t one…. in Android
it’s an Uncaught exception which means you can’t “handle” it or
recover from it like you maybe would in a .Net environment.

Xamarin(Mono) internally “handles” those uncaught exceptions by
surrounding literally everything with try-catch and raising the
Unhandled event but that is besides the point. It is also discouraged
to interact with the UI as well for varIoUs reasons.

Theoretically there are several “workarounds” for displaying a dialog
to the user or restarting the app,none of which I’d recommend on
doing. Instead you should surround sensitive areas with try-catch
clauses to handle expected exceptions,as for the unexpected one’s
just use an exception reporting component and update your app after
analyzing the reported exceptions

解释From

你也可以从应用程序中捕获未加扰的异常

创建名称ErrorActivity等基本活动

看看这个例子

protected override void OnCreate(Bundle bundle)
 {
        //register error handlers
                    AppDomain.CurrentDomain.UnhandledException += ErrorHandler.CurrentDomainOnUnhandledException;
                    TaskScheduler.UnobservedTaskException += ErrorHandler.TaskSchedulerOnUnobservedTaskException;
  }

在错误处理程序类中

public static class ErrorHandler
    {
        /// <summary>
        ///     Tasks the scheduler on unobserved task exception.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="unobservedTaskExceptionEventArgs">
        ///     The <see cref="UnobservedTaskExceptionEventArgs" /> instance containing
        ///     the event data.
        /// </param>
        public static void TaskSchedulerOnUnobservedTaskException(object sender,UnobservedTaskExceptionEventArgs unobservedTaskExceptionEventArgs)
        {
            var newExc = new Exception("TaskSchedulerOnUnobservedTaskException",unobservedTaskExceptionEventArgs.Exception);
            LogUnhandledException(newExc);
        }

        /// <summary>
        ///     Currents the domain on unhandled exception.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="unhandledExceptionEventArgs">
        ///     The <see cref="UnhandledExceptionEventArgs" /> instance containing the event
        ///     data.
        /// </param>
        public static void CurrentDomainOnUnhandledException(object sender,UnhandledExceptionEventArgs unhandledExceptionEventArgs)
        {
            var newExc = new Exception("CurrentDomainOnUnhandledException",unhandledExceptionEventArgs.ExceptionObject as Exception);
            LogUnhandledException(newExc);
        }

        /// <summary>
        ///     Logs the unhandled exception.
        /// </summary>
        /// <param name="exception">The exception.</param>
        internal static void LogUnhandledException(Exception exception)
        {
            try
            {
                string error =
                    $"Exception Caught:{DateTime.Now:F} The Error Message IS {exception.Message}\n\r full stack trace is {exception.ToString()} ";
#if DEBUG
                const string errorFileName = "errorlog.txt";
                var libraryPath = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
                // iOS: Environment.SpecialFolder.Resources
                var errorFilePath = System.IO.Path.Combine(libraryPath,errorFileName);
                System.IO.File.WriteAllText(errorFilePath,error);
                Android.Util.Log.Error("Crash Report error not handled",ex.ToString());
    #else
                    // Log to Android Device Logging.
                    Android.Util.Log.Error("Crash Report",error);
    #endif
                }
                catch (Exception ex)
                {
                    Android.Util.Log.Error("Crash Report error not handled",ex.ToString());
                    // just suppress any error logging exceptions
                }
            }
        }

现在你可以像这样继承ErrorActivity的所有活动

Public class Fooactivity:ErrorActivity
{
}

现在你可以在应用程序中处理错误了.所以你从日志文件..或Android设备日志监视器获取错误日志.希望这有助于……