Gridview值中的下拉列表

Question

我動態地將值添加到dropDownlist中，該值是Gridview中的列之一。

問題在於，當添加新行？時，下拉列表中選擇的值不會保存或維護。 知道我做錯了什么。 這是我的代碼..

這是我的Gridview

   <asp:GridView ID="GridView1" runat="server" CellPadding="4" ForeColor="#333333" GridLines="None" OnDataBound="GridView1_DataBound">
                    <AlternatingRowStyle BackColor="White" />
                    <Columns>
                        <asp:boundfield datafield="ID" headertext="categoryid" />
<asp:boundfield datafield="univirsity" headertext="category name" />

                        <asp:templatefield headertext="products">
<itemtemplate>
<asp:dropdownlist id="dropdownlist1" runat="server">
</asp:dropdownlist>
</itemtemplate>
</asp:templatefield>
                    </Columns>

                </asp:GridView>

這是單擊按鈕時將數據動態綁定到Gridview的代碼。

if (!Page.IsPostBack)
            {
                DataTable dt = new DataTable();
                dt.Columns.Add("ID", System.Type.GetType("System.Int32"));
                dt.Columns.Add("univirsity", System.Type.GetType("System.Int32"));
                dt.Columns.Add("major", System.Type.GetType("System.Int32"));
                Session["MyDataTable"] = dt;
            }

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            DataTable t = (DataTable)Session["MyDataTable"];
            DataRow row1 = t.NewRow();

            row1["ID"] = t.Rows.Count + 1;
            row1["univirsity"] = 3;
           // row1["major"] = 31;
            t.Rows.Add(row1);

            Session["MyDataTable"] = t;
            GridView1.DataSource = t;
            GridView1.DataBind(); 
        }

 protected void GridView1_DataBound(object sender, EventArgs e)
        {
            //addControl();

            ArrayList list = new ArrayList();
            list.Add("DMG");
            list.Add("SVC");

            foreach (GridViewRow row in GridView1.Rows)
            {
                // int key = (int)GridView1.DataKeys[row.RowIndex].Value;
                if (row.RowType == DataControlRowType.DataRow)
                {
                    DropDownList dl = (DropDownList)row.FindControl("dropdownlist1");

                    string sel = dl.SelectedValue;
                    if (!String.IsNullOrEmpty(sel))
                    {
                        dl.DataSource = list;
                        dl.DataBind();
                        dl.SelectedValue = sel;
                    }
                    else
                    {
                        dl.DataSource = list;
                        dl.DataBind();

                    }

                }
            }
        }

Answer 1

您並不是在做任何“錯誤”的事情，只是在期待錯誤的事情。 模板控件（例如gridviews）以這種方式起作用。 如果要保留模板中控件的選定值，則必須自己執行。

我建議不要在Session中存儲大量數據，但我假設您知道這一點，並且您的方案不打算擴展到數以百萬計的用戶，每個用戶在該數據表中都有幾行。

對於您的情況，我將在該數據表中添加另一列以存儲“產品”值； 與每個回發進行同步，並在重新綁定時確保從表值設置dropdownlist值：-

protected override void OnLoad(EventArgs e)
{
    if (!Page.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("ID", typeof(int));
        dt.Columns.Add("univirsity", typeof(int));
        dt.Columns.Add("major", typeof(int));
        // our new column
        dt.Columns.Add("selectedProduct", typeof(string));
        Session["MyDataTable"] = dt;
    }
    else
    {
        // on each postback, loop through the grid and update
        // the datatable

        // get our table AsEnumerable, so we can use LINQ expressions on it
        var table = ((DataTable)Session["MyDataTable"]).AsEnumerable();

        foreach (GridViewRow gridRow in GridView1.Rows)
        {
            // get this row's ID from the grid
            int id = Convert.ToInt32(gridRow.Cells[0].Text);

            // and get the matching datarow from the table
            var tableRow = table.Where(x => (int)x["ID"] == id)
                                .SingleOrDefault();

            if (tableRow != null)
            {
                var ddl = (DropDownList)gridRow.FindControl("dropdownlist1");
                tableRow["selectedProduct"] = ddl.SelectedValue;
            }
        }
    }

    base.OnLoad(e);
}

void button1_Click(object sender, EventArgs e)
{
    DataTable t = (DataTable)Session["MyDataTable"];
    DataRow   row1 = t.NewRow();

    row1["ID"] = t.Rows.Count + 1;
    row1["univirsity"] = 3;
    // set default value for new column
    row1["selectedProduct"] = "DMG";

    t.Rows.Add(row1);

    Session["MyDataTable"] = t;
    GridView1.DataSource = t;
    GridView1.DataBind();
}

protected void GridView1_DataBound(object sender, EventArgs e)
{
    ArrayList list = new ArrayList();
    list.Add("DMG");
    list.Add("SVC");

    // get our table again
    var table = ((DataTable)Session["MyDataTable"]).AsEnumerable();

    foreach (GridViewRow gridRow in GridView1.Rows)
    {
        if (gridRow.RowType == DataControlRowType.DataRow)
        {
            // get our id and tablerow again
            int id = Convert.ToInt32(gridRow.Cells[0].Text);
            var tableRow = table.Where(x => (int)x["ID"] == id)
                                .SingleOrDefault();

            // bind the list
            DropDownList dl = (DropDownList)gridRow.FindControl("dropdownlist1");
            dl.DataSource = list;
            dl.DataBind();

            // set value from tablerow.selectedProduct
            dl.SelectedValue = (string)tableRow["selectedProduct"];
        }
    }
}

Answer 2

當您在gridview中有新行時，是否嘗試使用循環重新加載該下拉列表？