2 Dropdownlists in Gridview cause error: Databinding methods such as Bind() can only be used in the context of a databound control

问题

Though this seems to be discussed before, I can't apply given help in my case:

I have 2 DropDownLists (DDL1, DDL2) inside the Edit Template of a Gridview, which is bound to a SQLDataSource. DDL2 depends on the selected value of DDL1.

If I place the SQLDataSources that populate the DropDownLists on the top level, the ControlID of DDL2's ControlParameter isn't found even though I address it correctly (Gridview$DDL1ControlID). Therefore I placed the SQLDataSources inside the Edit Template of the Gridview. Now both DropDownLists are populated correctly if I enter in Edit Mode for a given Record; if I change the Index for DDL1, DDL2 is not updated automatically, as DDL2 has AutoPostBack set to false. Once I set AutoPostBack to true, the error "Databinding methods such as Eval(), XPath(), and Bind() can only be used in the " is thrown.

    <asp:GridView runat="server" ID="Gridview1" 
                  DataSourceID="Milestones" 
                  DataKeyNames="ID"
                  OnRowEditing="OnRowEditing"
                  OnRowDataBound="OnRowDataBoundMS"
                  OnSelectedIndexChanged="OnSelectedIndexChangedMS">
....
            <asp:templatefield HeaderText="Default Owner Group" ItemStyle-HorizontalAlign="center">
            <ItemTemplate>
                <asp:Label runat="server" Text='<%# Bind("DefaultOwnerGroup") %>' id="LabelDefaultOwnerGroup" Font-Size="12px" Width="50px"/>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:SqlDataSource runat="server" id="OwnerGroups" ProviderName="System.Data.SqlClient"
                    ConnectionString="Data Source=XXXXX"    
                    SelectCommand="select function, 2 as ord
                                   from Staff
                                   where function is not null
                                   group by function
                                   union all
                                   select 'select' as function, 0 as ord
                                   union all
                                   select '-----' as function, 1 as ord
                                   order by ord, function">
                </asp:SqlDataSource>
                <asp:DropDownList runat="server" id="DDOwnerGroup" Text='<%# Bind("DefaultOwnerGroup") %>' DataSourceID="OwnerGroups" DataTextField="function" DataValueField="function" Font-Size="12px" Width="80px" AutoPostBack="true"/>
            </EditItemTemplate>
        </asp:templatefield>

        <asp:templatefield HeaderText="Default Owner" ItemStyle-HorizontalAlign="center">
            <ItemTemplate>
                <asp:Label runat="server" Text='<%# Bind("DefaultOwner") %>' id="LabelDefaultOwner" Font-Size="12px" Width="50px"/>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:SqlDataSource runat="server" id="Owner" ProviderName="System.Data.SqlClient" 
                    ConnectionString="Data Source=XXXXX"    
                    SelectCommand="select Name, UserID
                                   from Staff
                                   where function = @OwnerGroup
                                   union all
                                   select Null as Name, Null as UserID
                                   order by Name">
                <SelectParameters>
                    <asp:ControlParameter ControlID="DDOwnerGroup" PropertyName="SelectedValue" Name="OwnerGroup"  Type="String" />
                </SelectParameters>
                </asp:SqlDataSource>
                <asp:DropDownList runat="server" id="DDOwner" Text='<%# Bind("DefaultOwner") %>' Width="100px" DataSourceID="Owner" DataTextField="Name" DataValueField="UserID" Font-Size="12px"/>
            </EditItemTemplate>
        </asp:templatefield>

回答1:

I bind the DropdownLists in the OnRowDataBound Event like this:

            <asp:templatefield HeaderText="Default Owner Group" ItemStyle-HorizontalAlign="center">
            <ItemTemplate>
                <asp:Label runat="server" Text='<%# Bind("DefaultOwnerGroup") %>' id="LabelDefaultOwnerGroup" Font-Size="12px" Width="50px"/>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:Label runat="server" Text='<%# Bind("DefaultOwnerGroup") %>' id="LabelDefaultOwnerGroupEdit" Visible="false"/>
                <asp:SqlDataSource runat="server" id="OwnerGroups" ProviderName="System.Data.SqlClient"
                    ConnectionString="Data Source=XXXXX"    
                    SelectCommand="...">
                </asp:SqlDataSource>
                <asp:DropDownList runat="server" id="DDOwnerGroup" DataSourceID="OwnerGroups" DataTextField="funcion" DataValueField="funcion" Font-Size="12px" Width="80px" AutoPostBack="true"/>
            </EditItemTemplate>
        </asp:templatefield>

        <asp:templatefield HeaderText="Default Owner" ItemStyle-HorizontalAlign="center">
            <ItemTemplate>
                <asp:Label runat="server" Text='<%# Bind("DefaultOwner") %>' id="LabelDefaultOwner" Font-Size="12px" Width="50px"/>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:Label runat="server" Text='<%# Bind("DefaultOwner") %>' id="LabelDefaultOwnerEdit" Visible="false"/>
                <asp:SqlDataSource runat="server" id="Owner" ProviderName="System.Data.SqlClient" 
                    ConnectionString="Data Source=XXXXX"    
                    SelectCommand="...."
                <SelectParameters>
                    <asp:ControlParameter ControlID="DDOwnerGroup" PropertyName="SelectedValue" Name="OwnerGroup"  Type="String" />
                </SelectParameters>
                </asp:SqlDataSource>
                <asp:DropDownList runat="server" id="DDOwner" Width="100px" DataSourceID="Owner" DataTextField="Name" DataValueField="UserID" Font-Size="12px"/>
            </EditItemTemplate>
        </asp:templatefield>

protected void OnRowDataBoundMS(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        if ((e.Row.RowState & DataControlRowState.Edit) > 0)
        {
            DropDownList DDL1 = e.Row.FindControl("DDOwnerGroup") as DropDownList;
            DropDownList DDL2 = e.Row.FindControl("DDOwner") as DropDownList;
            Label LBL1 = e.Row.FindControl("LabelDefaultOwnerGroupEdit") as Label;
            Label LBL2 = e.Row.FindControl("LabelDefaultOwnerEdit") as Label;
            DDL1.SelectedValue = Convert.ToString(LBL1.Text);
            DDL2.DataBind();
            DDL2.SelectedValue = Convert.ToString(LBL2.Text);
        }
    }
}

来源：https://stackoverflow.com/questions/39206045/2-dropdownlists-in-gridview-cause-error-databinding-methods-such-as-bind-can