Test first component.

VisualComponentsForm/VisualComponentsForm/FormMain.Designer.cs

@@ -1,6 +1,6 @@
 namespace VisualComponentsForm
 {
-    partial class Form1
+    partial class FormMain
     {
         /// <summary>
         ///  Required designer variable.
@@ -28,10 +28,10 @@
         /// </summary>
         private void InitializeComponent()
         {
-            this.components = new System.ComponentModel.Container();
-            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
-            this.ClientSize = new System.Drawing.Size(800, 450);
-            this.Text = "Form1";
+            components = new System.ComponentModel.Container();
+            AutoScaleMode = AutoScaleMode.Font;
+            ClientSize = new Size(800, 450);
+            Text = "Form1";
         }
 
         #endregion

VisualComponentsForm/VisualComponentsForm/FormMain.cs

@@ -1,8 +1,8 @@
 namespace VisualComponentsForm
 {
-    public partial class Form1 : Form
+    public partial class FormMain : Form
     {
-        public Form1()
+        public FormMain()
         {
             InitializeComponent();
         }

VisualComponentsForm/VisualComponentsForm/FormMain.resx

@@ -18,7 +18,7 @@
     <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
     <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
     <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
-    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing"">Blue</data>
     <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
         <value>[base64 mime encoded serialized .NET Framework object]</value>
     </data>

VisualComponentsForm/VisualComponentsForm/Program.cs

@@ -11,7 +11,7 @@ namespace VisualComponentsForm
             // To customize application configuration such as set high DPI settings or default font,
             // see https://aka.ms/applicationconfiguration.
             ApplicationConfiguration.Initialize();
-            Application.Run(new Form1());
+            Application.Run(new FormMain());
         }
     }
 }

VisualComponentsLib/CustomListBox/MyListBox.cs

@@ -8,6 +8,40 @@ namespace VisualComponentsLib.CustomListBox
 {
     public class MyListBox : ListBox
     {
+        //получение выбранного значения
+        string _chooiceElem { get; set; } = string.Empty;
 
+        //делегат на смену значения
+        public delegate void GetNewVal(string data, EventArgs e);
+
+        //событие
+        public event GetNewVal ChangeSelectedVal;
+
+        //base constructor; привязываем событие к делегату
+        public MyListBox() : base() 
+        {
+            ChangeSelectedVal += _changeSelectedVal;
+        }
+
+        public void _addNewElem(string data)
+        {
+            Items.Add(data);
+        }
+
+        public void _clearListBox()
+        {
+            Items.Clear();
+        }
+
+        public void _clickToList(string data, EventArgs e)
+        {
+            ChangeSelectedVal(data, e);
+        }
+
+        //перезапись поля при событии смены значения
+        public void _changeSelectedVal(string data, EventArgs e)
+        {
+            _chooiceElem = data;
+        }
     }
 }