组合框选择的值未获取

Question

这是我用来加载组合框的函数。 我可以加载组合框，但是当我尝试获取组合框的selectedvalue ，它显示为null ； 我没有得到实际价值。

public static DataTable GetComboBoxedDataTable(DataTable oldDataTable, string valueColumn, string textColumn, string topRowValue, string topRowText, ComboBox cmb)
{
    DataTable newDataTable = new DataTable();
    newDataTable.Columns.Add(valueColumn);
    newDataTable.Columns.Add(textColumn);
    foreach (DataRow oldDR in oldDataTable.Rows)
    {
        DataRow newDR = newDataTable.NewRow();
        newDR[0] = oldDR[valueColumn].ToString();
        newDR[1] = oldDR[textColumn].ToString();
        newDataTable.Rows.InsertAt(newDR, newDataTable.Rows.Count);
    }

    // Add your 'Select an item' option at the top
    DataRow dr = newDataTable.NewRow();
    dr[0] = topRowValue;
    dr[1] = topRowText;
    newDataTable.Rows.InsertAt(dr, 0);

    cmb.ValueMember = valueColumn;
    cmb.DisplayMember = textColumn;
    return newDataTable;
}

填充组合框的代码：

PolosysHMS.General.Classes.GeneralClass.GetComboBoxedDataTable(ds.Tables[0], "RoomID", "RoomNo", "0", "Select", cmbroomno);

我需要combobox.selectedvalue的代码：

private void cmbroomno_SelectedIndexChanged(object sender, EventArgs e)
        {
            try
            {
                object[,] ParamArray = new object[,] { { "@RoomID", cmbroomno.SelectedValue } };---code where i need selected value
                DataSet ds = new DataSet();
                ds = DB.ExecuteQuery_SP("SelectGuestDetailsForService", ParamArray);

填充组合框的代码：

Answer 1

您错过了设置数据集的机会。

cmb.DataSource = newDataTable 
cmb.ValueMember = valueColumn;
cmb.DisplayMember = textColumn;
return newDataTable;

Answer 2

首先，您应该更改代码以填充组合框。 它看起来很奇怪。

public static DataTable GetComboBoxedDataTable(DataTable oldDataTable, string valueColumn, string textColumn, string topRowValue, string topRowText, ComboBox cmb)
{
    DataTable newDataTable = oldDataTable.Copy();
    DataRow dr = newDataTable.NewRow();
    dr[0] = topRowValue;
    dr[1] = topRowText;
    newDataTable.Rows.InsertAt(dr, 0);

    cmb.ValueMember = valueColumn;
    cmb.DisplayMember = textColumn;
    cmb.DataSource = newDataTable;
    return newDataTable;
} 

第二件事是声明一个多维数组来存储值

private void cmbroomno_SelectedValueChanged(object sender, EventArgs e)
{
    object[,] ParamArray = new object[,] { { "@RoomID", cmbroomno.SelectedValue } };
    DataSet ds = DB.ExecuteQuery_SP("SelectGuestDetailsForService", ParamArray);
}