Question

我的网页上有两个下拉列表。第二个依赖于第一个加载。例如，如果第一个是“墨尔本”，第二个列出墨尔本的所有郊区。

代码完全正常工作，但是当我第一次加载页面时，第二个dropdownlist2没有填充。我需要再次选择“墨尔本”以填充第二个下拉列表。

这是我的Page load

代码

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        if (Session["Username"] == null)
        {
            Response.Redirect("LoginPage.aspx");
        }

        if (getAccess(Session["Username"].ToString()) == false)
        {
            Response.Redirect("Unauthorized.aspx");
        }

        DataSet ds = GetAllCategory();
        if (ds.Tables.Count > 0)
        {
            DropDownList1.DataTextField = "identifier";
            DropDownList1.DataValueField = "OS_ID"; //Change field to one you want.
            DropDownList1.DataSource = ds.Tables[0];
            DropDownList1.DataBind();
        }
    }
}

这是选择的索引更改代码

 protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    DataSet ds = softwareType(Convert.ToInt32(DropDownList1.SelectedValue));
    if (ds.Tables.Count > 0)
    {
        DropDownList2.DataTextField = "identifier";
        DropDownList2.DataValueField = "ST_ID"; //Change field to one you want.
        DropDownList2.DataSource = ds.Tables[0];
        DropDownList2.DataBind();
    }
}

我不确定如何解决这个简单的问题？

Answer 1

一个想法可能是GetAllCategory的第一个值在页面加载时绑定第二个dropdown list。

public void PopulateDropdownList2(int selectedValue)
{
    DropDownList2.Items.Clear();
    DataSet ds = softwareType(selectedValue);
    if (ds.Tables.Count > 0)
    {
           DropDownList2.DataTextField = "identifier";
           DropDownList2.DataValueField = "ST_ID"; //Change field to one you want.
           DropDownList2.DataSource = ds.Tables[0];
           DropDownList2.DataBind();
    }
}

在

上调用上述功能

if (!Page.IsPostBack)
{

}

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        if (Session["Username"] == null)
        {
            Response.Redirect("LoginPage.aspx");
        }

        if (getAccess(Session["Username"].ToString()) == false)
        {
            Response.Redirect("Unauthorized.aspx");
        }

        DataSet ds = GetAllCategory();
        if (ds.Tables.Count > 0)
        {
            DropDownList1.DataTextField = "identifier";
            DropDownList1.DataValueField = "OS_ID"; //Change field to one you want.
            DropDownList1.DataSource = ds.Tables[0];
            DropDownList1.DataBind();
            PopulateDropdownList2(Convert.ToInt32(ds.Tables[0].Rows[0]["identifier"].ToString()));
        }

    }
}

Answer 2

试试这个

    DataSet ds = GetAllCategory();
    if (ds.Tables.Count > 0)
    {
        DropDownList1.DataTextField = "identifier";
        DropDownList1.DataValueField = "OS_ID"; //Change field to one you want.
        DropDownList1.DataSource = ds.Tables[0];
        DropDownList1.DataBind();
    }

   if(DropDownList1.Items.Count > 0)
   { 
       DropDownList1.SelectedIndex = 0;
       DropDownList1_SelectedIndexChanged(this,null);
   }

Answer 3

使用您的标记更新，您是否设置了Autopost="true"，或者您可以使用Ajaxtoolkit's cascading dropdowns

Answer 4

尝试在DropDownList1.DataBind（）;

下添加此行

DropDownList1.SelectedIndex = 0;

Answer 5

在页面加载时调用此if（！ispostback）以及选择第一个ddl的索引更改

private void fillSecondDdl()
{
DataSet ds = softwareType(Convert.ToInt32(DropDownList1.SelectedValue));
    if (ds.Tables.Count > 0)
    {
        DropDownList2.DataTextField = "identifier";
        DropDownList2.DataValueField = "ST_ID"; //Change field to one you want.
        DropDownList2.DataSource = ds.Tables[0];
        DropDownList2.DataBind();
    }
}

Answer 6

最后在页面加载中调用此函数

fillSecondDropdown(Convert.ToInt32(DropDownList1.SelectedValue));



 public void  fillSecondDropdown(int firstdropdownValue)
    {
    DataSet ds = softwareType(firstdropdownValue);
        if (ds.Tables.Count > 0)
        {
            DropDownList2.DataTextField = "identifier";
            DropDownList2.DataValueField = "ST_ID"; //Change field to one you want.
            DropDownList2.DataSource = ds.Tables[0];
            DropDownList2.DataBind();
        }
    }

Answer 7

我将函数从DropDownList1_SelectedIndexChanged（）中重构出来并将其放入一个新函数中：

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
   ddl1Changed(DropDownList1.SelectedValue);
}

public void ddl1Changed(string selectedValue)
{
    DataSet ds = softwareType(Convert.ToInt32(selectedValue));
    if (ds.Tables.Count > 0)
    {
        DropDownList2.DataTextField = "identifier";
        DropDownList2.DataValueField = "ST_ID"; //Change field to one you want.
        DropDownList2.DataSource = ds.Tables[0];
        DropDownList2.DataBind();
    }
}

然后

您的Page_Load上的

：

public void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        if (Session["Username"] == null)
        {
            Response.Redirect("LoginPage.aspx");
        }

        if (getAccess(Session["Username"].ToString()) == false)
        {
            Response.Redirect("Unauthorized.aspx");
        }

        DataSet ds = GetAllCategory();
        if (ds.Tables.Count > 0)
        {
            DropDownList1.DataTextField = "identifier";
            DropDownList1.DataValueField = "OS_ID"; //Change field to one you want.
            DropDownList1.DataSource = ds.Tables[0];
            DropDownList1.DataBind();
        }

        ddl1Changed("Melbourne");
    }


}

在页面加载上填充两个下拉列表

7 个答案: