尝试将数据插入数据库时​​抛出异常错误

Question

我收到一个错误，抛出一个像标题一样的异常。我不确定是什么问题

连接：

    public void connectToDatabase()
    {
        connStrBuilder = new SqlConnectionStringBuilder();
        connStrBuilder.DataSource = @"DESK-KEGRC\SQLSERVER";
        connStrBuilder.InitialCatalog = "RentalDatabase";
        connStrBuilder.IntegratedSecurity = true;

        connection = new SqlConnection(connStrBuilder.ToString());

    }

    public void Insert(Car car)
    {
        try
        {
            string commandText = "INSERT INTO dbo.Cars(Brand, Name, Year) VALUES (@Brand, @Name, @Year)";
            SqlCommand command = new SqlCommand(commandText, connection);
            command.Parameters.AddWithValue("@Brand", car.newBrand);
            command.Parameters.AddWithValue("@Name", car.newName);
            command.Parameters.AddWithValue("@Year", car.newRegisteredYear);
            connection.Open();
            command.ExecuteNonQuery();
        }
        catch
        {
            throw;
        }
    }

这是将数据插入数据库的事件按钮

 private void InsertData(object sender, EventArgs e)
    {
        car = new Car();
        car.newBrand = txtBrand.Text;
        car.newName = txtName.Text;
        car.newRegisteredYear = txtYear.Text;
        dataBaseConnection.Insert(car);
    }

错误：

  

System.NullReferenceException：未将对象引用设置为对象的实例。      at ConnectToDatabase.DatabaseConnection.Insert（Car car）在C：\ Users \ Kopalnia \ Desktop \ C＃\ Program \ VehicleRental \ VehicleRental \ Vehicle Rental \ ConnectToDatabase \ DatabaseConnection.cs：第46行      at Vehicl_Rental.AddACar.InsertData（Object sender，EventArgs e）位于C：\ Users \ Kopalnia \ Desktop \ C＃\ Program \ VehicleRental \ VehicleRental \ Vehicle Rental \ Vehicl Rental \ AddACar.cs：第31行

Answer 1

您必须先致电connectToDatabase()：

private void InsertData(object sender, EventArgs e)
{
        connectToDatabase()
        car = new Car();
        car.newBrand = txtBrand.Text;
        car.newName = txtName.Text;
        car.newRegisteredYear = txtYear.Text;
        dataBaseConnection.Insert(car);
}