我有一个带有3个组合框和1个按钮的Asp.net页面。第一个组合框选择将影响另外2个组合框数据源。我正在使用回调函数为其他组合框设置数据源。 在用户从所有组合框中选择之后，用户单击该按钮并生成回发。 我的问题是服务器端代码，不知道页面中的选择， 如果我试图从组合框中获取值，我总是得到null。 寻找解决方案。
谢谢。
代码
Code of aspx
<script type="text/javascript">
// <![CDATA[
function OnProductChange(cb_Products) {
cb_Packing.PerformCallback(cb_Products.GetValue().toString());
cb_ProductionSite.PerformCallback(cb_Products.GetValue().toString());
}
function OnPackChange(cb_Products) {
ASPxComboBox1.PerformCallback(cb_Packing.GetValue().toString());
}`enter code here`
function OnFactoryChange(cb_Products) {
cb_ProductionSite.PerformCallback();
}
// ]]>
</script>
<PanelCollection>
<dx:PanelContent runat="server" SupportsDisabledAttribute="True">
<dx:ASPxLabel ID="ASPxLabel1" runat="server" Font-Bold="True" Font-Names="Snap ITC"
Font-Size="Medium" Font-Underline="True" ForeColor="#333333" Text="Production Form (DEMO)">
</dx:ASPxLabel>
<br />
<br />
<dx:ASPxLabel ID="ASPxLabel2" runat="server" Font-Names="Berlin Sans FB Demi" Font-Size="Medium"
Text="Select Product" ForeColor="#FF3300">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="cb_Products" runat="server" ValueType="System.String" Font-Names="Berlin Sans FB Demi"
DataSourceID="EntityDataSource1" Spacing="3" TextField="PC_Name" EnableSynchronization="False"
ValueField="PCID" ClientIDMode="Static" DropDownStyle="DropDownList">
<Columns>
<dx:ListBoxColumn Caption="Product's name" FieldName="PCID" Visible="false" />
<dx:ListBoxColumn Caption="Product's name" FieldName="PC_Name" />
</Columns>
<ClientSideEvents SelectedIndexChanged=" function(s,e) { OnProductChange(s); }" />
</dx:ASPxComboBox>
<asp:EntityDataSource ID="EntityDataSource1" runat="server" ConnectionString="name=TrackQREntities"
DefaultContainerName="TrackQREntities" EnableFlattening="False" EntitySetName="TrackQR_ProductsCatalog"
Select="it.[PC_Name], it.[PCID]" Where="it.[ClientID] == 11">
</asp:EntityDataSource>
<br />
<br />
<dx:ASPxLabel ID="ASPxLabel3" runat="server" Font-Names="Berlin Sans FB Demi" Font-Size="Medium"
Text="Packing Options" ForeColor="#FF3300">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="cb_Packing" runat="server" Font-Names="Berlin Sans FB Demi"
ValueType="System.String" ClientIDMode="Static" DropDownStyle="DropDown" EnableSynchronization="False"
OnCallback="Packing_Callback" TextField="PackQuantity"
ValueField="PackID" ClientInstanceName="cb_Packing"
EnableCallbackMode="True">
<Columns>
<dx:ListBoxColumn FieldName="PackID" Visible="False" />
<dx:ListBoxColumn Caption="Pack Quantity" FieldName="PackQuantity" />
</Columns>
<ClientSideEvents SelectedIndexChanged=" function(s,e) { OnPackChange(s); }" />
</dx:ASPxComboBox>
<br />
<br />
<dx:ASPxLabel ID="ASPxLabel4" runat="server" Font-Names="Berlin Sans FB Demi" Font-Size="Medium"
Text="Production Site" ForeColor="#FF3300">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="cb_ProductionSite" runat="server" Font-Names="Berlin Sans FB Demi"
ValueType="System.String" ClientIDMode="Static" DropDownStyle="DropDown" EnableSynchronization="False"
TextField="LLName" ValueField="LLID"
ClientInstanceName="cb_ProductionSite" EnableCallbackMode="True"
OnCallback="cb_ProductionSite_Callback"
>
<Columns>
<dx:ListBoxColumn FieldName="LLID" Visible="False" />
<dx:ListBoxColumn Caption="Factory Name" FieldName="LLName" />
</Columns>
<ClientSideEvents SelectedIndexChanged=" function(s,e) { OnFactoryChange(s); }" />
</dx:ASPxComboBox>
<br />
<br />
<dx:ASPxLabel ID="ASPxLabel5" runat="server" Font-Names="Berlin Sans FB Demi" Font-Size="Medium"
Text="Number of Products" ForeColor="#FF3300">
</dx:ASPxLabel>
<dx:ASPxTextBox ID="atb_Quantity" runat="server" Width="170px">
</dx:ASPxTextBox>
<br />
<dx:ASPxButton ID="ab_Produce" runat="server" Text="Produce"
Font-Names="Arial Black" Font-Size="Medium" OnClick="ab_Produce_Click"
CssFilePath="~/App_Themes/SoftOrange/{0}/styles.css" CssPostfix="SoftOrange"
SpriteCssFilePath="~/App_Themes/SoftOrange/{0}/sprite.css">
</dx:ASPxButton>
<dx:ASPxComboBox ID="ASPxComboBox1" runat="server" Font-Names="Berlin Sans FB Demi"
ValueType="System.String" ClientIDMode="Static" DropDownStyle="DropDown" EnableSynchronization="False"
TextField="LLName" ValueField="LLID"
ClientInstanceName="cb_ProductionSite" EnableCallbackMode="True"
OnCallback="cb_ProductionSite_Callback"
>
<Columns>
<dx:ListBoxColumn FieldName="LLID" Visible="False" />
<dx:ListBoxColumn Caption="Factory Name" FieldName="LLName" />
</Columns>
<ClientSideEvents SelectedIndexChanged=" function(s,e) { OnFactoryChange(s); }" />
</dx:ASPxComboBox>
<br />
<br />
</dx:PanelContent>
Code of aspx.cs
protected void Packing_Callback(object sender, DevExpress.Web.ASPxClasses.CallbackEventArgsBase e)
{
//if (e.Parameter != "")
//{
using (TrackQREntities te = new TrackQREntities())
{
int id = int.Parse(e.Parameter);
var product = te.TrackQR_ProductsCatalog.Where(s => s.PCID == id).FirstOrDefault();
cb_Packing.DataSource = product.TrackQR_PacksType.ToList();
cb_Packing.DataBind();
cb_Products.SelectedIndex = id;
// }
}
}
protected void cb_ProductionSite_Callback(object sender, DevExpress.Web.ASPxClasses.CallbackEventArgsBase e)
{
if (e.Parameter != "")
{
using (TrackQREntities te = new TrackQREntities())
{
cb_ProductionSite.DataSource = te.TrackQR_LogisticLocations.Where(s => s.LLTypesID == 1).ToList();
cb_ProductionSite.DataBind();
}
}
}
protected void ab_Produce_Click(object sender, EventArgs e)
{
cb_ProductionSite.Value.ToString(); <--- Error Value is null