DropDownList返回NULL [英] DropDownList returning NULL

问题描述

我有一个DDL，该DDL根据另一个DDL的选择绑定到SQL Server表，并根据选择将文本插入到Label中.问题在于标签要么没有获取数据，要么DDL向标签提供了NULL.请在下面检查我的代码并帮助解决.谢谢.

I have a DDL that is bound to a SQL Server table depending on the selection of another DDL and inserting text into a Label depending on the selection. The problem is that the label is either not getting the data or the DDL are providing NULL to the label. Please check my code below and help resolve. Thank you.

protected void Page_Load(object sender, EventArgs e)
    {
        if(DropDownList1.SelectedIndex > 0)
        BindDropDownList2(DropDownList1.SelectedItem.Text);
    }

    protected void Button2_Click(object sender, EventArgs e)
    {
           if (DropDownList1.SelectedIndex == 5)
                if (DropDownList2.SelectedIndex == 3)
                       Label1.Text = "You selected index 5 from ddl1 and index 3 from ddl2";

    }

private void BindDropDownList2(string field)
    {
        if (DropDownList1.SelectedIndex != 5)
        {
            con.ConnectionString = strcon;
            com.Connection = con;
            con.Open();

            string strQuery = @"SELECT " + DropDownList1.SelectedItem.Text + " FROM NUMS";
            da = new SqlDataAdapter(strQuery, con);
            da.Fill(ds);

            DropDownList2.DataSource = ds;
            DropDownList2.DataTextField = field;
            DropDownList2.DataValueField = field;
            DropDownList2.DataBind();

            con.Close();
        }
        else
        {
            DropDownList2.Items.Clear();
            DropDownList2.Items.Add("");
            DropDownList2.Items.Add("A");
            DropDownList2.Items.Add("B");
        }
    }

推荐答案

嗨 在页面 _Load
中使用 isPostBack

Hi use isPostBack in Page_Load

protected void Page_Load(object sender, EventArgs e)
    {
        if(!isPostBack)
        {
            if(DropDownList1.SelectedIndex > 0)
            BindDropDownList2(DropDownList1.SelectedItem.Text);
        }   
    }

谢谢

Thanks,

在页面加载时添加此代码

add this code at page load

if(isPostBack)
    return;

并将ddl autopostback属性设为true

and make the ddl autopostback property true

this will help.

try dis

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