Question

I need a way to bind multiple drop down lists that are populated based on their parent node.

RootDDL <- child <- grandchild[]

The code looks something similar to

<FormView DataSoureceID="rootDatasource">
    <DropDownList ID="RootDLL" AutoPostBack="true">
        <!--items-->
    </DropDownList>
    <DropDownList ID="child" AutoPostBack="true" DataSourceID="ChildDataSource" />
    <SqlDataSource ID="ChildDataSource" />

    <DropDownList ID="grandchild" DataSourceID="GrandChildDataSource" SelectedValue='<%# Bind('SomeFieldInRootDatasource') %>' />
    <SqlDataSource ID="GrandChildDataSource">
        <SelectParameters>
            <ControlParameter ControlID="child" PropertyName="SelectedValue" />
        </SelectParameters>
    </SqlDataSource>
    <Button Command="Update" />
</FormView>
<SqlDataSource ID="rootDatasource">
    <InsertParameters>
        <asp:Parameter Name="SomeFieldInRootDatasource" />
    </InsertParameters>
    <UpdateParameters>
        <asp:Parameter Name="SomeFieldInRootDatasource" />
    </UpdateParamters>
</SqlDataSource>

Changing the rootDDL works, unfortunately when the Child selectedvalue changes the grand child <%# Bind %> tries to rebind but cannot as it the FormView is no longer acting as a container.

It fails with

Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.

Is there any solution to this problem that will not require me to add event (multiple) handlers?

Answer 1

I ended up creating a hiddenfield for each child dropdownlist that I then bound with the value I needed. I created a generic indexchange handler to then update the hiddenfeild with the desired result. This results in the bound field not being updated by a datasource (avoiding the rebind system call that was causing the issue in the first place).

Not sure if this is the best solution but it should work for most cases.