2-Way Binding with CascadingDropDown

This post deals with 2-way binding of data to a CascadingDropDown. It assumes that the CascadingDropDown is already configured to return data to the list.

I had my DropDownList and CascadingDropDown pairs within a FormView and it is bound to a SqlDataSource.

<asp:Label ID="Label1" runat="server" Text="Mfr" />

<asp:DropDownList ID="ddlMfrs" runat="server" />

<cc1:CascadingDropDown ID="cddMfr" runat="server" TargetControlID="ddlMfrs" Category="MfrID" PromptText="Select a manufacturer" ServicePath="MfrService.asmx" ServiceMethod="GetMfrs" ContextKey="M" SelectedValue='<%# BIND("MfrID") %>'>

</cc1:CascadingDropDown>

When the data is being bound (i.e. Selecting) there is no problem. If the MfrID value is a 3 then it selects the item from the drop down list with a 3 like it should. The issue occurred when the data was being updated back to the database. The error I received was that the input was not in the correct format.

When I checked the NewValues of MfrID in FormView ItemUpdating I saw that the value wasn’t a 3 but rather 3:::MfrName. The error makes sense now since the sproc was looking for an integer for its MfrID parameter.

Since this was my only page using the CascadingDropDown I dealt with the error on in its code behind. I added the following to the FormView’s ItemUpdating:

Protected Sub fv1_ItemUpdating(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.FormViewUpdateEventArgs) Handles fv1.ItemUpdating

Dim strTemp As String

Dim strKey As String

For Each strKey In e.NewValues.Keys

strTemp = e.NewValues(strKey).ToString

If strTemp.Contains(":::") Then

e.NewValues(strKey) = CleanBindValue(strTemp)

End If

End Sub

And this is the CleanBindValue function that gets called:

Private Function CleanBindValue(ByVal DirtyValue As String) As String

'CascadingDropDown returns BIND values as value:::text

'and needs to be cleaned prior to database update

Dim strSplit() As String

strSplit = DirtyValue.Split(":::")

Return strSplit(0).ToString

End Function

Now the CleanBindValue function returns just the integer and the updates proceeds normally.

C# Code for the above two functions:

protected void FormView1_ItemUpdating(object sender, FormViewUpdateEventArgs e)

{

string strTemp;

foreach (string strKey in e.NewValues.Keys)

{

strTemp = (string)e.NewValues[strKey];

if (strTemp.Contains(":::"))

{

e.NewValues[strKey] = CleanBindValue(strTemp);

}

private string CleanBindValue(string DirtyValue)

{

string[] strSplit;

string strDelimiter = ":::";

char[] chDelimiter = strDelimiter.ToCharArray();

strSplit = DirtyValue.Split(chDelimiter);

return strSplit[0];

}

Technorati Tags: ASP.Net,AJAX,CSharp

posted on Wednesday, October 01, 2008 9:08 AM

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# re: 2-Way Binding with CascadingDropDown 11/27/2008 12:47 PM Javier

Do you have the code in C# I get a bit anoyed sometimes with VB.

Thanks,

Javier

# re: 2-Way Binding with CascadingDropDown 2/7/2009 9:36 AM HUSSEIN

THANKS

SAVED ME A LOT OF TROUBLE

# re: 2-Way Binding with CascadingDropDown 8/25/2009 7:48 AM Lennox McKenzie

It's quirky, but this saved my butt. The only issue I had was a boolean value in my EditTemplate.

protected void DetailsView1_ItemUpdating(object sender, DetailsViewUpdateEventArgs e) {
var strTemp = string.Empty;

foreach (var strKey in e.NewValues.Keys) {
if (!(e.NewValues[strKey] is string))
//skip anything we can't cast to a string
continue;

strTemp = (string)e.NewValues[strKey];

if (strTemp.Contains(":::"))
e.NewValues[strKey] = cleanBindValue(strTemp);
}
}

private object cleanBindValue(string DirtyValue) {
var delim = ":::".ToCharArray();

return DirtyValue.Split(delim)[0];
}

# re: 2-Way Binding with CascadingDropDown 9/4/2009 6:54 AM Agony

I realize this is kinda old, but I had to thank you for this. Saved me ton of headache!!!!! Thank you, thank you, thank you. I ended up creating a custom control inheriting from CascadingDropDown and adding a bindable property, clean up the selected value there and setting the property on load.

using System;
using System.ComponentModel;
using System.Web.UI;
using AjaxControlToolkit;

namespace CustomServerControls {
[ToolboxData("<{0}:SmartCascadingDropDown runat=server></{0}:smartCascadingDropDown>")]
public class SmartCascadingDropDown : CascadingDropDown {

private char[] _seperator = ":::".ToCharArray();

private string _DropDownSelectedValue;

[Bindable(BindableSupport.Yes)]
[Category("Data")]
[Browsable(true)]
[EditorBrowsable(EditorBrowsableState.Always)]
public string DropDownSelectedValue {
get {
return _DropDownSelectedValue;
}
set {
_DropDownSelectedValue = value;
}
}

protected override void OnLoad(EventArgs e) {
base.OnLoad(e);

_DropDownSelectedValue = cleanUpValue(base.SelectedValue);
}

private string cleanUpValue(string inputString) {
var outputString = inputString.Split(_seperator)[0];

return outputString;
}
}
}

# re: 2-Way Binding with CascadingDropDown 9/4/2009 7:01 AM Agony

Forgot to add, set properties for control as:

SelectedValue='<%# Eval("FieldID") >'
DropDownSelectedValue='<%# Bind("FieldID") %>'

I'm sure I could have overriden SelectedValue, but I prefer not to risk breaking any existing functionality so I can use the derived CascadingDropDown like a normal one if I need to.

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