从后台代码显示之前，如何在弹出窗口中选择预填充的下拉列表选项

Question

This line sets the selected index to the correct number:

    ddlCliNewMsg.SelectedIndex = ddlCliNewMsg.Items.IndexOf(ddlCliNewMsg.Items.FindByValue(dr["ClientText"].ToString()));

But when the popup loads, the 0 index is selected.

Answer 1

Change

    if (dr["ClientText"].ToString().Length > 0)
    {
    ddlCliNewMsg.SelectedValue = dr["ClientText"].ToString();
    }

To

    if (dr["ClientText"].ToString().Length > 0)
    {
    ddlCliNewMsg.ClearSelection(); //making sure the previous selection has been cleared
    ddlCliNewMsg.Items.FindByValue(dr["ClientText"].ToString()).Selected = true;
    }

Answer 2

    for populating dropdownlist use below code:

ddlCliNewMsg.DataSource = dataSource;
ddlCliNewMsg.DataTextField = textField;
ddlCliNewMsg.DataValueField = valueField;
ddlCliNewMsg.DataBind();

    textField and valueField is data field for text and value of dropdownlist.
    for selecting item with your value use below code:

 ddlCliNewMsg.Items.FindByValue("your value").Selected = true;

    replace your value with "your value"