如何从数据库填充组合框并在C＃中的索引零上插入新项 [英] How to populate combo box from database and insert new item on index zero in C#

问题描述

下面的代码对我有用，但是我无法插入---选择---到第一个索引值为零。



我尝试过：

This code below works for me, but i have not been able to insert ---Select--- to the for first index with value zero.

What I have tried:

private void LoadGrade()
    {
        using (SQLiteConnection conn = new SQLiteConnection(connstring))
        {

            try
            {
                string query = "select GradeCode, GradeName from Grade";
                SQLiteDataAdapter da = new SQLiteDataAdapter(query, conn);
                conn.Open();
                DataSet ds = new DataSet();
                da.Fill(ds, "OrgGrade");
                cboGrade.Items.Insert(0,"---Select---);
                cboGrade.DisplayMember = "GradeName";
                cboGrade.ValueMember = "GradeCode";
                cboGrade.DataSource = ds.Tables["OrgGrade"];

            }
            catch (Exception ex)
            {

                MessageBox.Show("Error occured loading grade!");
            }
        }
    } 

但它对我不起作用。我还希望能够在从数据库中检索时检索并显示组合框上的displaymember和displayvalue，而不会重复项目

but it is not working for me. Also i want to able to retrieve and display the displaymember and displayvalue on the combo box while retrieving from database without items not being repeated

推荐答案

尝试

try

DataTable dt = new DataTable();
           dt.Columns.Add("GradeName");
           dt.Columns.Add("GradeCode");
           dt.Rows.Add("aaa", "11");
           var row = dt.NewRow();
           row["GradeName"] = "Select";
           row["GradeCode"] = "0";
           dt.Rows.InsertAt(row, 0);
           cboGrade.DisplayMember = "GradeName";
           cboGrade.ValueMember = "GradeCode";
           cboGrade.DataSource = dt;

您无法直接在ComboBox上工作，因为您已将其绑定到DataSet。相反，您需要使用 DataRowCollection.InsertAt方法（DataRow，Int32）（System.Data） [ ^ ]



所以示例可能是（未经测试） ：

You can't work directly on the ComboBox as you have bound it to a DataSet. Instead, you need to work with where the data is located using DataRowCollection.InsertAt Method (DataRow, Int32) (System.Data)[^]

So example could be (untested):

var insertRow = ds.Details.NewDetailsRow();

insertRow.Id = "0";
insertRow.Description = "---Select---";

ds.Details.Rows.InsertAt(insertRow, 0);

private void LoadGrade()
    {
        using (SQLiteConnection conn = new SQLiteConnection(connstring))
        {
 
            try
            {
                string query = "select GradeCode, GradeName from Grade";
                SQLiteDataAdapter da = new SQLiteDataAdapter(query, conn);
                conn.Open();
                DataSet ds = new DataSet();
                da.Fill(ds, "OrgGrade");
                
                cboGrade.DisplayMember = "GradeName";
                cboGrade.ValueMember = "GradeCode";
                cboGrade.DataSource = ds.Tables["OrgGrade"];
                cboGrade.Items.Insert(0,"---Select---);
 
            }
            catch (Exception ex)
            {
 
                MessageBox.Show("Error occured loading grade!");
            }
        }
    } 

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