Handle closing of window

Elwig/Windows/AdministrationWindow.cs

@@ -2,6 +2,7 @@ using Elwig.Helpers;
 using Elwig.Models;
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Linq;
 using System.Threading.Tasks;
 using System.Windows;
@@ -30,6 +31,7 @@ namespace Elwig.Windows {
                 LockContext = IsEditing;
             }
         }
+        protected bool IsClosing { get; private set; }
 
         private TextBox[] TextBoxInputs;
         private TextBox[] PlzInputs;
@@ -55,6 +57,7 @@ namespace Elwig.Windows {
             RadioButtonInputs = Array.Empty<RadioButton>();
             Valid = new();
             OriginalValues = new();
+            Closing += OnClosing;
             Loaded += OnLoaded;
         }
 
@@ -75,6 +78,10 @@ namespace Elwig.Windows {
             ValidateRequiredInputs();
         }
 
+        private void OnClosing(object? sender, CancelEventArgs evt) {
+            IsClosing = true;
+        }
+
         private ComboBox GetPlzOrtInput(TextBox input) {
             return PlzOrtInputs[Array.IndexOf(PlzInputs, input)];
         }
@@ -244,7 +251,7 @@ namespace Elwig.Windows {
         }
 
         protected bool InputLostFocus(TextBox input, ValidationResult res, string? msg = null) {
-            if (!res.IsValid)
+            if (!res.IsValid && !IsClosing)
                 System.Windows.MessageBox.Show(res.ErrorContent.ToString(), msg ?? res.ErrorContent.ToString(), MessageBoxButton.OK, MessageBoxImage.Warning);
             return res.IsValid;
         }