Question

我有这个C＃代码，我使用的是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();

        }
    }

当我尝试设置我的2个文本框时，使用以下代码更改我的组合框的值：

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：＆＃39; System.Data.Entity.DynamicProxies.Employers_4603A50E3C8B2711C02C0DAE379C7EC403103DB450E8CCC08E7874FDC1318E90＆＃39;类型＆＃39; System.IConvertible＆＃39;。＆＃39;

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：＆＃39;无法对类型为＆＃; Db.Employers＆＃39;的对象执行强制转换。类型＆＃39; System.IConvertible＆＃39;。＆＃39;

如果我尝试转换为String而不是long并将字符串放入消息框中，我会得到2次＆＃39; Db.Employers＆＃39;从第三个开始，ID的数值就像在我的组合框中一样。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();

    }
}

如果要更改文本值以与comboBox中的选定值相关联，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;       
    }
  }

comboBox_TextChanged上的combobox.selectedvalue无法正常工作

1 个答案: