Untis-API Optimierung.

LehrerApp.Desktop/Views/Groups/GroupDetailView.axaml.cs

@@ -13,6 +13,7 @@ using LehrerApp.Desktop.Views.Shared;
 using LehrerApp.Desktop.Views.Students;
 using LehrerApp.Desktop.Views.Workload;
 using Microsoft.Extensions.DependencyInjection;
+using System.Globalization;
 using System.Text;
 
 namespace LehrerApp.Desktop.Views.Groups;
@@ -174,7 +175,7 @@ public partial class GroupDetailView : UserControl
             var values = new[]
             {
                 student.LongName ?? student.Name, student.ForeName, student.Gender,
-                student.BirthDate?.ToString() ?? student.BirthDateRaw, student.ClassName,
+                FormatBirthDate(student), student.ClassName,
                 student.ExternKey.ToString(), student.Address.Email, student.Address.Mobile,
                 student.Address.Phone, student.Address.City, student.Address.PostCode, student.Address.Street,
             };
@@ -183,6 +184,17 @@ public partial class GroupDetailView : UserControl
         return new ImportFile("webuntis-students.csv", Encoding.UTF8.GetBytes(builder.ToString()));
     }
 
+    private static string? FormatBirthDate(UntisStudentDto student)
+    {
+        if (student.BirthDate is not { } normalizedDate) return student.BirthDateRaw;
+
+        var value = normalizedDate.ToString("D8", CultureInfo.InvariantCulture);
+        return DateOnly.TryParseExact(value, "yyyyMMdd", CultureInfo.InvariantCulture,
+            DateTimeStyles.None, out var date)
+            ? date.ToString("dd.MM.yyyy", CultureInfo.InvariantCulture)
+            : student.BirthDateRaw;
+    }
+
     private static string SafeTsv(string? value) => (value ?? "").Replace('\t', ' ')
         .Replace('\r', ' ').Replace('\n', ' ');