DropDownList：SelectedIndexChanged不触发

Question

I fill a ASP Dropdownlist in the pageload

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {           
                for (int i = 0; i < _maxStationsAnz; i++)
                {
                    String stations = arrayList[1];

                    _allData = stations.Split(Convert.ToChar("/"));
                    _data = _allData[i].Split(Convert.ToChar(";"));

                    ddWeatherstations.Items.Add(_data[0]);
                }
        }

When a new station is selected, it should update informations. I use the OnSelectedIndexChanged attribute on my aspx site.

My code behind:

protected void ddWeatherstations_SelectedIndexChanged(object sender, EventArgs e)
    {
        for (int i = 0; i < _maxStationsAnz; i++)
        {
            if (ddWeatherstations.SelectedIndex == i)
            {
                  lselected.Text = "Index changed!";
                  //unimportant code
                  //....
            }
        }
    }

When I set a breakpoint and run the program and change the value of the dropdownlist, nothing happens.

Answer 1

You need to set AutoPostBack property of your dropdownlist ddWeatherstations to True .

Try This:

<asp:DropDownList ID="ddWeatherstations" runat="server" AutoPostBack="true" 
    OnSelectedIndexChanged="ddWeatherstations_SelectedIndexChanged">
</asp:DropDownList>

Answer 2

您需要设置属性AutoPostBack="true"但是每次您选择DropDownList的其他索引时，这都会回发所有页面，因此我建议您将DropDownList放入AJAX更新面板中。