DataRowView而不是值

Question

每当我试图运行我的应用程序时，我都会得到一个错误，因为我没有得到comboBox.SelectedValue的实际值，而是得到了一个DataRowView项。

下面是我得到错误的代码：

private void InitDataGridView()
{
    query = "SELECT p.name, p.age FROM Person p INNER JOIN Class c ON p.idC=c.idC WHERE p.id=" 
            + comboBoxClass.SelectedValue;
    command = new SqlCommand(query, connection);
    adapter = new SqlDataAdapter(command);
    datatable = new DataTable();
    adapter.Fill(datatable);
    dataGridViewStudents.DataSource = datatable;
}

comboBoxClass.SelectedValue应该返回给我"idC"，因为我设置了DataSource、DisplayMember和(ValueMember -> idC)。

idC是主键(int)。

ComboBox设置：

comboBoxClass.DataSource = datatable;
comboBoxClass.DisplayMember = "className";
comboBoxClass.ValueMember = "idC";

Answer 1

好吧，我想出了我的代码出了什么问题。这既不是comboBox的初始化，也不是dataGridView的，但写错查询完全是我的错。

我感谢大家为帮助我而付出的努力。

Answer 2

不绑定或不正确地绑定ValueMember可以产生您所描述的确切效果。正如您在下面的片段中所看到的。

在ComboBox的初始化上放置一些断点，并找出为什么ValueMember不是您所需要的。然后，您的DataGridView应该正确地填充。

using System;
using System.Data;
using System.Drawing;
using System.Windows.Forms;

namespace BindingToDataTable_46914296
{


    public partial class Form1 : Form
    {
        ComboBox combob = new ComboBox();
        ComboBox combobFail = new ComboBox();
        TextBox txtbx = new TextBox();
        public Form1()
        {
            InitializeComponent();
            InitComboBox();
            InitComboBoxFail();
            InitTxtBx();
        }

        private void InitTxtBx()
        {
            txtbx.Location = new Point(5, 30);
            txtbx.Width = this.Width - 10;
            this.Controls.Add(txtbx);
        }

        /// <summary>
        /// This version works, the proper selected value shows up in the textbox
        /// </summary>
        private void InitComboBox()
        {
            combob.Location = new Point(5,5);
            this.Controls.Add(combob);

            DataTable dt = new DataTable();
            dt.Columns.Add(new DataColumn("Col1", typeof(string)));
            dt.Columns.Add(new DataColumn("Col2", typeof(string)));
            dt.Columns.Add(new DataColumn("Col3", typeof(string)));
            dt.Columns.Add(new DataColumn("Col4", typeof(Int32)));
            dt.Rows.Add("blah1", "bleh", "bloh", 1);
            dt.Rows.Add("blah2", "bleh", "bloh", 2);
            dt.Rows.Add("blah3", "bleh", "bloh", 3);
            dt.Rows.Add("blah4", "bleh", "bloh", 4);
            combob.DataSource = dt;
            combob.DisplayMember = "Col1";
            combob.ValueMember = "Col4";

            combob.SelectedValueChanged += Combob_SelectedValueChanged;
        }


        /// <summary>
        /// This version DOES NOT work, a DataRowView item appears in the textbox when the selection changes
        /// </summary>
        private void InitComboBoxFail()
        {
            combobFail.Location = new Point(combob.Location.X + combob.Width + 5, 5);
            this.Controls.Add(combobFail);

            DataTable dt = new DataTable();
            dt.Columns.Add(new DataColumn("Col1", typeof(string)));
            dt.Columns.Add(new DataColumn("Col2", typeof(string)));
            dt.Columns.Add(new DataColumn("Col3", typeof(string)));
            dt.Columns.Add(new DataColumn("Col4", typeof(Int32)));
            dt.Rows.Add("blah1", "bleh", "bloh", 1);
            dt.Rows.Add("blah2", "bleh", "bloh", 2);
            dt.Rows.Add("blah3", "bleh", "bloh", 3);
            dt.Rows.Add("blah4", "bleh", "bloh", 4);
            combobFail.DataSource = dt;
            combobFail.DisplayMember = "Col1";
            //only difference is I am not binding ValueMember

            combobFail.SelectedValueChanged += Combob_SelectedValueChanged;
        }

        private void Combob_SelectedValueChanged(object sender, EventArgs e)
        {
            txtbx.Text = ((ComboBox)sender).SelectedValue.ToString();
        }
    }
}