下拉列表的上一个item.text

Question

I am using MS VS 2010, and working on an ASP.NET C# website. I am stuck on something that I think may be quite simple, maybe not though.

Lets say I have a drop down list.

DropDownList ddl = new DropDownList();
ddl.ID = "d355";
dynamicPanel.Controls.Add(ddl);

ListItem lstItem1 = new ListItem();
lstItem1.Text = "1";
ListItem lstItem2 = new ListItem();
lstItem2.Text = "2";

ddl.Items.Add(lstItem1);
ddl.Items.Add(lstItem2);
ddl.SelectedIndexChanged += new EventHandler(this.ddl_SelectedIndexChanged);

Since we programatically created our drop down list, we need to also create our custom event handler that we tied to it.

protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
{
    // add the selected index to a counter
    counter +=((DropDownList)sender).SelectedIndex;
    // Now this is where I get stuck, if the current selected index is less
    // than the previous selected index, I want to subtract from the counter



}

This is where my problem lies. Please read the comments in the event handler. (Sorry if I have some of the syntax off, this is all free hand at the moment)

I have a feeling that I can get the previous selected index (or item it doesn't matter) from the event args ((DropDownList)e).?

Please help >.< This doesn't seem too bad!

Answer 1

I don't think that there is a built in mechanism, but you could use ViewState or a HiddenField to keep the previous index. Something like the following:

protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {
        int selectedIndex = ((DropDownList)sender).SelectedIndex;
        if (selectedIndex < (int)ViewState["PreviousIndex"])
        {
            counter -= ((DropDownList)sender).SelectedIndex;
        }
        else
        {
            counter += ((DropDownList)sender).SelectedIndex;
        }
        // update the index
        ViewState["PreviousIndex"] = selectedIndex;
    }