TextBox is remade with event.

CustomComponents/Exceptions/ContentException.cs

@@ -14,7 +14,7 @@ namespace CustomComponents.Exceptions
         {
             if(state)
             {
-                return "TextBox is empty however null flag is checked.";
+                return "TextBox is not empty however null flag is checked.";
             }
 
             return "TextBox is empty. You better write something!";

CustomComponents/TextBox.cs

@@ -58,23 +58,40 @@ namespace CustomComponents
             }
             catch(ContentException ex)
             {
-                taskHandler += (sender, e) => MessageBox.Show(ex.Message);
+                HandlerCreation(ex.Message);
             }
             taskHandler?.Invoke(this, e);
             
         }
             
-        private void CheckTextBoxValueType(object sender, EventArgs args)
+        private void CheckTextBoxValueType(object sender, EventArgs e)
         {
             Value = textBox.Text;
+
             try
             {
-                Convert.ToInt32(Value);
-            }
-            catch (Exception ex)
+                if(!Value.All(char.IsDigit))
                 {
-                MessageBox.Show(ex.ToString());
+                    throw new NotIntegerException(Value);    
                 }
             }
+            catch (NotIntegerException ex)
+            {
+                HandlerCreation(ex.Message);
+            }
+            taskHandler?.Invoke(this, e);
+        }
+
+        private void HandlerCreation(string message)
+        {
+            EventHandler handler = null;
+            handler = (sender, e) =>
+            {
+                MessageBox.Show(message);
+                taskHandler -= handler;
+            };
+
+            taskHandler += handler;
+        }
     }
 }