Jeff and .NET

Now if you could just hack in checkboxes like the comparable WinForms control I'd be ecstatic :)

Great job, btw.

Sorry, new to .net, can you please explain a little how to use your code?

Thanks,

Gustavo

10x man, great job !

If you want make custom control and share it with the world ;)

Great job!!!!!

Thanks a lot

:)

Pingback from  3f blog  » Blog Archive   » DropDownList y OptionGroups

This was a great starting point. The problem is that on a postback, the groups are lost because the fact it is an optgroup is not then picked up and re-rendered out.

The answer is not to use attributes as you suggest, but instead to set the "value" of the listitem which is to be the group header. Set it to something very unlikely to be used again like "$$GROUPHEADER$$GROUPHEADER$$"

Your test against the attribute (to see whether it is null) then becomes: "If item.Value = "$$GROUPHEADER$$GROUPHEADER$$" Then"

Next is to make it a bit easier for the programmer to add groups without having to remember this value string. To do this, I created a class called "OptionGroup" (I'm sure you can work out the contents of it) and then added a public sub on the control you wrote:

       Public Sub AddOptionGroup(ByVal og As OptionGroup)

           Dim optGrpTitle As New ListItem(og.GroupName, "$$GROUPHEADER$$GROUPHEADER$$")

           Me.Items.Add(optGrpTitle)

           For Each li As ListItem In og.Items

               Me.Items.Add(New ListItem(li.Text, li.Value))

           Next

       End Sub

To then add groups in an .aspx page:

   Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

       If Not IsPostBack Then

           Dim G1Items As New ListItemCollection

           G1Items.Add(New ListItem("G1V1", "G1V1"))

           G1Items.Add(New ListItem("G1V2", "G1V2"))

           G1Items.Add(New ListItem("G1V3", "G1V3"))

           Dim G2Items As New ListItemCollection

           G2Items.Add(New ListItem("G2V1", "G2V1"))

           G2Items.Add(New ListItem("G2V2", "G2V2"))

           G2Items.Add(New ListItem("G2V3", "G2V3"))

           Dim og1 As New OptionGroup("Group1", G1Items)

           Dim og2 As New OptionGroup("Group2", G2Items)

           Me.ddlTest.AddOptionGroup(og1)

           Me.ddlTest.AddOptionGroup(og2)

       End If

   End Sub

Except for that the code remains the same, and works perfectly across postbacks.

This is because the value property of the items does persist in viewstate, I suppose.

Anyway an excellent article, thanks.

Ben.

Well, you could use a control that already has that.

It has about the same code as this one presented here, but also a few more tricks, like finding out to which group does the selected item belongs to.

Check it out

www.codeplex.com/SharpPieces

Hi Jeff,

This is the solution that exactly I need. Thanks to you.

Thank you to Ben Sloan as well, for fixing the "PostBack" problems.

This is a great article.

Regards,

Dzaki.

HI thanks for submitting the very useful code

but i am not being able to add items in dropdownlist

will u please tell me how can i add items as well as groups in dropdown list.

my code is running fine and has no error.but dont know how to add items with option group.

thanks

By CodeProject url:

www.codeproject.com/.../DropDownListOptionGroup.aspx

Add this to method in ur Class file.

protected override object SaveViewState()

{

// Create an object array with one element for the CheckBoxList's

// ViewState contents, and one element for each ListItem in skmCheckBoxList

object[] state = new object[this.Items.Count + 1];

object baseState = base.SaveViewState();

state[0] = baseState;

// Now, see if we even need to save the view state

bool itemHasAttributes = false;

for (int i = 0; i < this.Items.Count; i++)

{

if (this.Items[i].Attributes.Count > 0)

{

itemHasAttributes = true;

// Create an array of the item's Attribute's keys and values

object[] attribKV = new object[this.Items[i].Attributes.Count * 2];

int k = 0;

foreach (string key in this.Items[i].Attributes.Keys)

{

attribKV[k++] = key;

attribKV[k++] = this.Items[i].Attributes[key];

}

state[i + 1] = attribKV;

}

}

// return either baseState or state, depending on whether or not

// any ListItems had attributes

if (itemHasAttributes)

return state;

else

return baseState;

}

protected override void LoadViewState(object savedState)

{

if (savedState == null) return;

// see if savedState is an object or object array

if (savedState is object[])

{

// we have an array of items with attributes

object[] state = (object[])savedState;

base.LoadViewState(state[0]); // load the base state

for (int i = 1; i < state.Length; i++)

{

if (state[i] != null)

{

// Load back in the attributes

object[] attribKV = (object[])state[i];

for (int k = 0; k < attribKV.Length; k += 2)

this.Items[i - 1].Attributes.Add(attribKV[k].ToString(), attribKV[k + 1].ToString());

}

}

}

else

// we have just the base state

base.LoadViewState(savedState);

}

i can not understand

RenderContents

not found override mthd

again

this.VerifyMultiSelect();

not found  

i want full code

i copy above top and make class and paste but no o/p

It would be nice to have a tutorial that explains how to use your code and get a drop down that is bindable to Database Tables(Table 1: OptionGroup, Table 2: Option Name).

This is bad example!

Hi.  Great posting.  Where does the Bold and Italics come from when the optgroup != null items are rendered? i.e. what if you wanted only italics.  How would you do that?

Thank you.