comboBox_TextChanged上的combobox.selectedvalue不能正常工作

Question

我有此C＃代码，并且我正在使用Sqlite

private void Form1_Load(object sender, EventArgs e)
    {
        using (var db = new mainEntities())
        {
            comboBox1.DataSource = db.Employers.ToList();
            comboBox1.DisplayMember = "Surname";
            comboBox1.ValueMember = "ID";

            //convert to long
            long id = Convert.ToInt64(comboBox1.SelectedValue);
            //get employer's ID
            var employer = (from s in db.Employers
                            where s.ID == id
                            select s).FirstOrDefault();
            //set 2 textboxes to Name and Surname values
            TextBox1.Text = employer.Name;
            TextBox2.Text = employer.Surname;
            db.SaveChanges();

        }
    }

当我尝试通过以下代码设置2个文本框更改组合框的值时：

private void comboBox1_TextChanged(object sender, EventArgs e)
    {

        long id = Convert.ToInt64(comboBox1.SelectedValue);
            using (var db = new mainEntities())
        {
            var employer = (from s in db.Employers
                            where s.ID == id
                            select s).FirstOrDefault();
            //set 2 textboxes to Name and Surname values
            TextBox1.Text = employer.Name;
            TextBox2.Text = employer.Surname;       
        }

我得到：System.InvalidCastException：'System.Data.Entity.DynamicProxies.Employers_4603A50E3C8B2711C02C0DAE379C7EC403103DB450E8CCC08E7874FDC1318E90'类型为'System.IConvertible'。'

如果我用此禁用代理创建：

this.Configuration.ProxyCreationEnabled = false;

在我的Db.context.cs中，我得到：System.InvalidCastException：'无法对类型为'System.IConvertible'的类型为'Db.Employers'的对象执行强制转换。

如果我尝试转换为String而不是long并将字符串放在消息框中，则得到的值是“ Db.Employers”的2倍，而从ID的第三个值开始，它就是组合框中的数值。 我哪里错了？

Answer 1

private void Form1_Load(object sender, EventArgs e)
{
    using (var db = new mainEntities())
    {
        comboBox1.DataSource = db.Employers.ToList();
        comboBox1.ValueMember = "ID";
        comboBox1.DisplayMember = "Surname";
        comboBox1.SelectedIndex =0;
        //convert to long
        long id = Convert.ToInt64(comboBox1.SelectedValue);
        //get employer's ID
        var employer = (from s in db.Employers
                        where s.ID == id
                        select s).FirstOrDefault();
        //set 2 textboxes to Name and Surname values
        TextBox1.Text = employer.Name;
        TextBox2.Text = employer.Surname;
        //db.SaveChanges();

    }
}

如果您想更改文本值以与comboBox中的选定值相关，则可以通过SelectedIndexChanged事件来实现

private void ComboBox1_SelectedIndexChanged(object sender,System.EventArgs e)
  {
    long id = Convert.ToInt64(comboBox1.SelectedValue);
        using (var db = new mainEntities())
    {
        var employer = (from s in db.Employers
                        where s.ID == id
                        select s).FirstOrDefault();
        //set 2 textboxes to Name and Surname values
        TextBox1.Text = employer.Name;
        TextBox2.Text = employer.Surname;       
    }
  }