Update on Save event

bool isFavorite;
//btnSave
private void btnSave_Click(object sender, EventArgs e)
{
    var textBoxes = new Dictionary<Control, string>()
    {
        {txtType, "Type" },
        {txtEngines, "Engines" },
        {txtSeats, "Seats" },
        {txtSpecialLivery, "Special Livery" }
    };

    // Check for empty values
    var emptyFields = new List<string>();

    foreach (var kvp in textBoxes)
    {
        if (kvp.Key is TextBox textBox)
        {
            if (string.IsNullOrWhiteSpace(textBox.Text) && (textBox.Visible || kvp.Value != "Special Livery"))
            {
                emptyFields.Add(kvp.Value);
            }
        }
    }

    // Message for empty values
    if (emptyFields.Any())
    {
        string message = "Please fill out the following fields:\n- " + string.Join("\n- ", emptyFields);
        MessageBox.Show(message);

        foreach (var kvp in textBoxes)
        {
            if ((kvp.Key is TextBox textBox && string.IsNullOrWhiteSpace(textBox.Text)))
            {
                kvp.Key.Focus();
                break;
            }
        }
        return; // Beende, wenn es leere Felder gibt
    }

    // Check for changes and only update changed values
    string updatedType = currentAircraft.Type;
    int updatedSeats = currentAircraft.Seats;
    string updatedEngines = currentAircraft.Engines;
    DateTime updatedFirstFlight = currentAircraft.FirstFlight;
    string updatedSpecialLivery = currentAircraft.SpecialLivery;
    string airline = currentAircraft.Airline;

    bool updatedIsFavorite;
    if(btnSetFavorite.Visible == true)
    {
        updatedIsFavorite = false;
    }
    else
    {
        updatedIsFavorite = true;
    }

    // Flag, um zu überprüfen, ob alle Daten korrekt sind
    bool isValid = true;

bool isFavorite;
//btnSave
private void btnSave_Click(object sender, EventArgs e)
{
    var textBoxes = new Dictionary<Control, string>()
    {
        {txtType, "Type" },
        {txtEngines, "Engines" },
        {txtSeats, "Seats" },
        {txtSpecialLivery, "Special Livery" }
    };

    // Check for empty values
    var emptyFields = new List<string>();

    foreach (var kvp in textBoxes)
    {
        if (kvp.Key is TextBox textBox)
        {
            if (string.IsNullOrWhiteSpace(textBox.Text) && (textBox.Visible || kvp.Value != "Special Livery"))
            {
                emptyFields.Add(kvp.Value);
            }
        }
    }

    // Message for empty values
    if (emptyFields.Any())
    {
        string message = "Please fill out the following fields:\n- " + string.Join("\n- ", emptyFields);
        MessageBox.Show(message);

        foreach (var kvp in textBoxes)
        {
            if ((kvp.Key is TextBox textBox && string.IsNullOrWhiteSpace(textBox.Text)))
            {
                kvp.Key.Focus();
                break;
            }
        }
        return; // Beende, wenn es leere Felder gibt
    }

    // Check for changes and only update changed values
    string updatedType = currentAircraft.Type;
    int updatedSeats = currentAircraft.Seats;
    string updatedEngines = currentAircraft.Engines;
    DateTime updatedFirstFlight = currentAircraft.FirstFlight;
    string updatedSpecialLivery = currentAircraft.SpecialLivery;
    string airline = currentAircraft.Airline;

    bool updatedIsFavorite;
    if(btnSetFavorite.Visible == true)
    {
        updatedIsFavorite = false;
    }
    else
    {
        updatedIsFavorite = true;
    }

    // Flag, um zu überprüfen, ob alle Daten korrekt sind
    bool isValid = true;