Hello.
I have a postback problem with viewstate.
I've searched the group and found many threads about this, but I still
can't understand...
I have this code:
DataSet ds = null;
if(! this.IsPostBack){
....
} else{
    StringReader sr = new StringReader((String)(ViewState["ds"]));
    ds.ReadXml(sr);
}

and I get an InvalidCastException.
BTW, I've chosen the name "ds" for the ViewState; I can't see on the
plain-vanilla microsoft documentation what is supposed to be that very
string value; I assume it can be any string (always the same, of
course). Am I right?
Could you please tell me what's wrong?

Thanks :)

DataSet ds = null;
...
...
...
} else{
StringReader sr = new StringReader((String)(ViewState["ds"]));

Wut is ds ??? is it a dataset object or StringReader ???
How i interpretted it as was you are trying to type cast dataset into a string ! ! ! !

you wud have dione something like this ??? ViewState.Add("ds" , OBJECT) -- champ0007Posted from http://www.pcreview.co.uk/ newsgroup access

Thanks for your answer.
The complete code is:
// BEGIN
DataSet ds = null;
if(! this.IsPostBack){
    try{
        ds = SqlHelper.ExecuteDataset(
            ConfigurationSettings.AppSettings["ConnectionString"]
            , CommandType.Text
            , "select UserID, Name, EmailUtente "
            + "from users "
            + "where CodiceCliente = '" + cc
            + "' order by Name asc"
            );
        UserIDResponsabile.DataSource = ds;
        UserIDResponsabile.DataTextField = "Name";
        UserIDResponsabile.DataValueField = "UserID";
        UserIDResponsabile.DataBind();
        //UserIDResponsabile.Items.Insert(0,new ListItem("","0"));
        StringWriter sw = new StringWriter();
        ds.WriteXml(sw);
        ViewState["ds"] = sw.ToString();
    }
    catch (Exception ex) {
        Orrore.Text = ex.Message.ToString();
    }
} else{
    StringReader sr = new StringReader((String)(ViewState["ds"]));
    ds.ReadXml(sr);
}
// END
and now the cast is OK; I used to do:
ViewState["ds"] = sw;
instead of:
ViewState["ds"] = sw.ToString();

But now I have a further problem; the next line (next to the cast):
ds.ReadXml(sr);
returns a NullReferenceException, because the variable "ds" (my
DataSet) is null.
How am I supposed to deal with this?

Thank you :)

Ooops... sorry, I just had to do:
ds = new DataSet();
before that.
I wonder why this piece of code is missing in my book...
Anyway, I just have another problem (that's the reason why I'm doing
this):
I have to use this DataSet in another method, the method that's
delegated for the SelectedIndexChanged event of my DropDownList.
In this method I'm doing:
foreach(DataRow riga in
((DataSet)UserIDResponsabile.DataSource).Tables[0].Rows){
but this line gives a NullReferenceException

Basically I'd just like to read the new selected value of the list and
find out the corresponding email-value in the dataset; that is, I have
the username in the list and I want to find out its email (that's
stored in the DataSet but not in the list).
I mean, the user clicks on the dropdownlist and selects a name. Then
the following textbox (readonly) is supposed to get filled with the
email of the selected name, automatically.
How can I do it?

Thank you ^^

May be you can try in your Method thats for SelectedIndexedChanged
Get the Current Value which is selected in the ListBox and with that Value
you can do Dataset.select("email = " & Value) --- basically a where caluse in the saying email = "xyz "
This way you'll get the row containing email corresponding to the name, which you can bind with the Textbox  !! !
Your Nullreference Exception is it :::: Object Reference Not set to instance of the Object ?????
If thats the Exception its that you havent instantiated an object... jst do new object ! ! ! and it'll solve the thing !
I hope that helps ! -- champ0007Posted from http://www.pcreview.co.uk/ newsgroup access

Yeah! Great! :)
I've solved it this way:
DataSet uDataSet;
DropDownList UsersList;
private void Page_Load(object sender, System.EventArgs e) {
    ...
    uDataSet = Elenco_Utenti();
    ...
}
private DataSet Elenco_Utenti(){
    DataSet ds = null;
    ...
    return ds;
}
private void UsersList_SelectedIndexChanged(object sender,
System.EventArgs e){
    DataRow[] dr = uDataSet.Tables[0].Select("UserID = " +
UsersList.SelectedItem.Value);
    EmailResponsabile.Text = dr[0].ItemArray[2].ToString();
}

Thank you very much :D

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