Visual Web Developer在表格单元格中放置下拉菜单

Question

我已经创建了一个显示表格的网页。表格中的大多数单元格已经填充，但其中一些需要用户输入。我想在其中一些表格单元格中放置下拉菜单，这样单元格将填充从菜单中选择的内容，下拉列表将消失。

我已经让它在一个单元格中工作。然而，当我试图让它在第二个单元中工作时，一切都崩溃了。为了找出这个问题，我花了太多的时间，我甚至不确定我现在是如何让第一个问题生效的。:-)

相关代码如下：

protected void Page_Load(object sender, EventArgs e)
{

    // Create a DropDownList control.
    DropDownList DropList = new DropDownList();

    // Set the properties for the DropDownList control.
    DropList.ID = "TrendList";
    DropList.AutoPostBack = true;

    // Manually register the event-handling method for the 
    // SelectedIndexChanged event.
    DropList.SelectedIndexChanged += new EventHandler(this.Selection_Change);

    // Because the DropDownList control is created dynamically each
    // time the page is loaded, the data must be bound to the
    // control each time the page is refreshed.

    // Specify the data source and field names for the Text and 
    // Value properties of the items (ListItem objects) in the
    // DropDownList control.
    DropList.DataSource = CreateDataSource();
    DropList.DataTextField = "ColorTextField";
    DropList.DataValueField = "ColorValueField";

    // Bind the data to the control.
    DropList.DataBind();

    // Set the default selected item when the page is first loaded.
    if (!IsPostBack)
    {
        DropList.SelectedIndex = 0;
    }

    // Add the DropDownList control to the Controls collection of 
    // the PlaceHolder control.
    p1.Controls.Add(DropList);
    p2.Controls.Add(DropList);
}

ICollection CreateDataSource()
{

    // Create a table to store data for the DropDownList control.
    DataTable dt = new DataTable();

    // Define the columns of the table.
    dt.Columns.Add(new DataColumn("ColorTextField", typeof(String)));
    dt.Columns.Add(new DataColumn("ColorValueField", typeof(String)));

    // Populate the table with sample values.
    dt.Rows.Add(CreateRow("GreenUp", "GreenUp", dt));
    dt.Rows.Add(CreateRow("GreenFlat", "GreenFlat", dt));
    dt.Rows.Add(CreateRow("GreenDown", "GreenDown", dt));
    dt.Rows.Add(CreateRow("YellowUp", "YellowUp", dt));
    dt.Rows.Add(CreateRow("YellowFlat", "YellowFlat", dt));
    dt.Rows.Add(CreateRow("YellowDown", "YellowDown", dt));
    dt.Rows.Add(CreateRow("RedUp", "RedUp", dt));
    dt.Rows.Add(CreateRow("RedFlat", "RedFlat", dt));
    dt.Rows.Add(CreateRow("RedDown", "RedDown", dt));
    dt.Rows.Add(CreateRow("ClearUp", "ClearUp", dt));
    dt.Rows.Add(CreateRow("ClearFlat", "ClearFlat", dt));
    dt.Rows.Add(CreateRow("ClearDown", "ClearDown", dt));

    // Create a DataView from the DataTable to act as the data source
    // for the DropDownList control.
    DataView dv = new DataView(dt);
    return dv;

}

DataRow CreateRow(String Text, String Value, DataTable dt)
{

    // Create a DataRow using the DataTable defined in the 
    // CreateDataSource method.
    DataRow dr = dt.NewRow();

    // This DataRow contains the ColorTextField and ColorValueField 
    // fields, as defined in the CreateDataSource method. Set the 
    // fields with the appropriate value. Remember that column 0 
    // is defined as ColorTextField, and column 1 is defined as 
    // ColorValueField.
    dr[0] = Text;
    dr[1] = Value;

    return dr;
}

void Selection_Change(Object sender, EventArgs e)
{
    // Retrieve the DropDownList control from the Controls
    // collection of the PlaceHolder control.
    DropDownList DropList1 = (DropDownList)p1.FindControl("TrendList");
    DropDownList DropList2 = (DropDownList)p2.FindControl("TrendList");
    switch (sender.ToString())
    {
        case "p1":
            s1.InnerHtml = DropList1.SelectedItem.Value;
            break;
        case "p2":
            s2.InnerHtml = DropList2.SelectedItem.Value;
            break;
    }
}

下面是表中的相关代码片段：

<td><span id="s1" runat="server"><asp:PlaceHolder ID="p1" runat="server"></asp:PlaceHolder></span>
<td><span id="s2" runat="server"><asp:PlaceHolder ID="p2" runat="server"></asp:PlaceHolder></span>

现在我意识到开关控制是完全错误的，因为发送者不代表呼叫者的id。但我需要一些方法来区分哪个下拉菜单是调用者，以便我知道要替换哪个HTML。而且，我一次只能显示一个下拉菜单。

任何建议都是值得感谢的。

致以问候。

Answer 1

下面的代码解决了这个问题：

public void EditTable()
{
    ICollection trends = CreateDataSource();
    for (int x = 1; x <= 27; x++)
    {
        DropDownList ddl = new DropDownList();
        string index = x.ToString();
        ddl.ID = "TrendList" + index;
        ddl.AutoPostBack = true;
        ddl.SelectedIndexChanged += new EventHandler(this.Selection_Change);
        ddl.DataSource = trends;
        ddl.DataTextField = "TrendTextField";
        ddl.DataValueField = "TrendValueField";
        ddl.DataBind();
        if (!IsPostBack)
        {
            ddl.SelectedIndex = 0;
        }
        HtmlGenericControl span = (HtmlGenericControl)form1.FindControl("s" + index);
        PlaceHolder placeHolder = (PlaceHolder)span.FindControl("p" + index);
        if (placeHolder != null)
        {
            placeHolder.Controls.Add(ddl);
        }
    }
}