Adding full DI navigation example for testing purposes.

- adding internal private field into FormBase class
- adding Extension methods into DependencyInjection namespace for use
- adding 2 NavigateTo extension methods for DI using ServiceProvider
- adding example project
- adding to readme as example

TelegramBotBase/DependencyInjection/Extensions.cs

@@ -0,0 +1,86 @@
+using Microsoft.Extensions.DependencyInjection;
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Text;
+using System.Threading.Tasks;
+using TelegramBotBase.Form;
+
+namespace TelegramBotBase.DependencyInjection
+{
+    public static class Extensions
+    {
+        internal static FieldInfo _ServiceProviderField = typeof(FormBase).GetField("_serviceProvider", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
+
+        /// <summary>
+        /// Use Dependency Injection to create new form and inject parameters. (Main variant)
+        /// </summary>
+        /// <typeparam name="NewForm"></typeparam>
+        /// <param name="args"></param>
+        /// <returns></returns>
+        public static async Task<NewForm> NavigateTo<NewForm>(this FormBase current_form, params object[] args)
+            where NewForm : FormBase
+        {
+            var _serviceProvider = current_form.GetServiceProvider();
+
+            var instance = ActivatorUtilities.CreateInstance(_serviceProvider, typeof(NewForm)) as NewForm;
+
+            if (instance == null)
+                return null; //throw new Exception("Could not instantiate new form via DI.");
+
+            instance.SetServiceProvider(_serviceProvider);
+
+            await current_form.NavigateTo(instance, args);
+
+            return instance;
+        }
+
+        /// <summary>
+        /// Use Dependency Injection to create new form and inject parameters. (Alternative variant)
+        /// </summary>
+        /// <param name="current_form"></param>
+        /// <param name="formBaseType"></param>
+        /// <param name="args"></param>
+        /// <returns></returns>
+        /// <exception cref="ArgumentException"></exception>
+        public static async Task<FormBase> NavigateTo(this FormBase current_form, Type formBaseType, params object[] args)
+        {
+            if (!typeof(FormBase).IsAssignableFrom(formBaseType))
+                throw new ArgumentException($"{nameof(formBaseType)} argument must be a {nameof(FormBase)} type");
+
+            var _serviceProvider = current_form.GetServiceProvider();
+
+            var instance = ActivatorUtilities.CreateInstance(_serviceProvider, formBaseType) as FormBase;
+
+            if (instance == null)
+                return null; //throw new Exception("Could not instantiate new form via DI.");
+
+            instance.SetServiceProvider(_serviceProvider);
+
+            await current_form.NavigateTo(instance, args);
+
+            return instance;
+        }
+
+        /// <summary>
+        /// Sets the internal service provider field.
+        /// </summary>
+        /// <param name="form"></param>
+        /// <param name="serviceProvider"></param>
+        public static void SetServiceProvider(this FormBase form, IServiceProvider serviceProvider)
+        {
+            _ServiceProviderField?.SetValue(form, serviceProvider);
+        }
+
+        /// <summary>
+        /// Gets the internal service provider field value.
+        /// </summary>
+        /// <param name="form"></param>
+        /// <returns></returns>
+        public static IServiceProvider GetServiceProvider(this FormBase form)
+        {
+            var sp = _ServiceProviderField?.GetValue(form) as IServiceProvider;
+            return sp;
+        }
+    }
+}