.

VisualComponentsLib/CustomListBox/UserListBox.Designer.cs

@@ -29,6 +29,9 @@
         private void InitializeComponent()
         {
             listBox = new ListBox();
+            buttonAdd = new Button();
+            textBox = new TextBox();
+            buttonRemove = new Button();
             SuspendLayout();
             // 
             // listBox
@@ -41,20 +44,54 @@
             listBox.Size = new Size(234, 229);
             listBox.TabIndex = 0;
             // 
+            // buttonAdd
+            // 
+            buttonAdd.Location = new Point(261, 52);
+            buttonAdd.Name = "buttonAdd";
+            buttonAdd.Size = new Size(114, 23);
+            buttonAdd.TabIndex = 1;
+            buttonAdd.Text = "Добавить";
+            buttonAdd.UseVisualStyleBackColor = true;
+            buttonAdd.Click += ButtonAdd_Click;
+            // 
+            // textBox
+            // 
+            textBox.Location = new Point(252, 12);
+            textBox.Name = "textBox";
+            textBox.Size = new Size(133, 23);
+            textBox.TabIndex = 2;
+            // 
+            // buttonRemove
+            // 
+            buttonRemove.Location = new Point(261, 96);
+            buttonRemove.Name = "buttonRemove";
+            buttonRemove.Size = new Size(114, 23);
+            buttonRemove.TabIndex = 3;
+            buttonRemove.Text = "Очистить список";
+            buttonRemove.UseVisualStyleBackColor = true;
+            buttonRemove.Click += ButtonRemove_Click;
+            // 
             // UserListBox
             // 
             AutoScaleDimensions = new SizeF(7F, 15F);
             AutoScaleMode = AutoScaleMode.Font;
+            Controls.Add(buttonRemove);
+            Controls.Add(textBox);
+            Controls.Add(buttonAdd);
             Controls.Add(listBox);
             Location = new Point(3, 5);
             MinimumSize = new Size(84, 53);
             Name = "UserListBox";
-            Size = new Size(240, 240);
+            Size = new Size(398, 240);
             ResumeLayout(false);
+            PerformLayout();
         }
 
         #endregion
 
         private ListBox listBox;
+        private Button buttonAdd;
+        private TextBox textBox;
+        private Button buttonRemove;
     }
 }

VisualComponentsLib/CustomListBox/UserListBox.cs

@@ -32,5 +32,20 @@ namespace VisualComponentsLib.CustomListBox
             add => listBox.Items.Add(value);
             remove => listBox.Items.Clear();
         }
+
+        private void ButtonAdd_Click(object sender, EventArgs e)
+        {
+            if (!string.IsNullOrEmpty(textBox.Text))
+            {
+                listBox.Items.Add(textBox.Text);
+
+                textBox.Text = string.Empty;
+            }
+        }
+
+        private void ButtonRemove_Click(object sender, EventArgs e)
+        {
+            listBox.Items.Clear();
+        }
     }
 }

VisualComponentsLib/VisualComponentsLib.csproj

@@ -9,6 +9,7 @@
 
   <ItemGroup>
     <Folder Include="CustomTextBox\" />
+    <Folder Include="CustomListBox\" />
     <Folder Include="CustomDataGridView\" />
   </ItemGroup>