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-   -   invalid cast exception (http://p2p.wrox.com/showthread.php?t=3012)

giulio_santorini August 20th, 2003 07:08 PM

invalid cast exception
I've got a little problem with my C# WinForms test application.
I would like to have a ComboBox showing a a visual value and some hidden values.
So I build a class able to store thoose values. This class called ListItem have got two private variable, one is a string containing the visual value, the

other one is a UDT variable. It is a struct called ValoriNascosti containing two variables a string and an int.
The costructor of ListItem store the three values (description, and the two of ValoriNascosti). There is two accessor methods that retrieve: the string of th

description; and another one retrieve a variable of type ValoriNascosti.

I create an ArrayList of ListItem in this way:
ArrayList elencoProdotti = new ArrayList();
elencoProdotti.Add(new ListItem("0001", 5, "Prodotto1"));

I populate the combo with the ArrayList:
this.comboBox1.DataSource = elencoProdotti;

Than I tell to the combo that the member to display is accessible from the method Descrizione:
comboBox1.DisplayMember = "Descrizione";
And the hidden value is accessible from the method AccessorValoriNascosti:
comboBox1.ValueMember = "AccessorValoriNascosti" ;

Thoose two are the accessors I was talking about.

When I run this I've got my dear combo with the visual data I've choose (like Prodotto1, Prodotto2, Prodotto3 etc...).

So I add code in the event SelectedIndexChanged, trying to show the hidden values when the combobox element changes. So I do this:
this.textBox1.Text = ((ValoriNascosti)this.comboBox1.SelectedValue).mod uli.ToString();
but I've got an invalid cast exception.
This line give the same error:
ValoriNascosti supporto = (ValoriNascosti)this.comboBox1.SelectedValue;

The value stored should be of valoriNascosti type... isn't right this way of casting?
I really don't have clues. :-Thanks for help.

Olorin August 21st, 2003 06:44 AM


che tipo di var e' "moduli" ?
Mi riferisco alla linea:
this.textBox1.Text = ((ValoriNascosti)this.comboBox1.SelectedValue).mod uli.ToString();

forse devi fare qualcosa tipo
this.textBox1.Text = (<classe di moduli>)(((ValoriNascosti)this.comboBox1.SelectedV alue).moduli).ToString();

ma non credo faccia molta differenza...

Sei sicuro che l'errore provenga da quella riga li'?
Dato che
ValoriNascosti supporto = (ValoriNascosti)this.comboBox1.SelectedValue;
da' lo stesso errore, io guarderei al SelectedValue del combo box...

..prova a fare un MessageBox nel SelectedIndexChanged event handler che ti lista i vari valori
del combo box (SelectedValue, SelectedItem, etc etc...


Ankur_Verma August 21st, 2003 08:04 AM

This code works

//declaration of the struct and the class
    struct ValoriNascosti
        public string valstring;
        public int valint;

    class ListItem
        private ValoriNascosti valone;
        private string Desc;

        public ListItem(string strVal,int intVal,string desc)
            valone.valstring = strVal;
            valone.valint = intVal;
            Desc = desc;

        public string getDesc
                return Desc;

        public ValoriNascosti getValone
                return valone;


//filling up
    ArrayList elencoProdotti = new ArrayList();
    elencoProdotti.Add(new ListItem("0001", 5, "Prodotto1"));
    elencoProdotti.Add(new ListItem("0002", 6, "Prodotto2"));
    elencoProdotti.Add(new ListItem("0003", 7, "Prodotto3"));

    this.testcombo.DataSource = elencoProdotti;
    this.testcombo.DisplayMember = "getDesc";
    this.testcombo.ValueMember = "getValone" ;

// usage
    MessageBox.Show(((ValoriNascosti)this.testcombo.Se lectedValue).valint.ToString());

I cannot point out the problem out of what you have described
in your query so just check this code to see if there is
anything I have done differently.


Ankur Verma
.Net and C++ Specialist
Wiley Tech Support

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