C# App Grid Navigation - InvalidCastException

Question

I get two errors if I click on the navigation menu during runtime? I am a beginner in C# and have no idea how to solve this problem.

var group = (SampleDataGroup)e.ClickedItem;
var groupId = group.UniqueId;
var item = (SampleDataItem)e.ClickedItem;
var itemId = item.UniqueId;

InvalidCastException:

In System.InvalidCastException ist eine Ausnahme vom Typ "AstroApp.exe" aufgetreten, doch wurde diese im Benutzercode nicht verarbeitet.

Zusätzliche Informationen: Das Objekt des Typs "AstroApp.Data.SampleDataItem" kann nicht in Typ "AstroApp.Data.SampleDataGroup" umgewandelt werden.

public class SampleDataItem : SampleDataGroup
{
    // add flag as last param
    public SampleDataItem(String uniqueId, String title, String subtitle,
    String imagePath, String description, String content, SampleDataGroup group, int intIsCustomNav): base(uniqueId, title, subtitle, imagePath, description)
    {
        this._content = content;
        this._group = group;
        this.intIsCustomNav = intIsCustomNav;
    }

    private string _content = string.Empty;
    public string Content
    {
        get { return this._content; }
        set { this.SetProperty(ref this._content,value);}
    }

    private void SetProperty(ref string p, string value)
    {
        throw new NotImplementedException();
    }

    private SampleDataGroup _group;
    public SampleDataGroup Group
    {
        get { return this._group; }
        set { this.SetProperty(ref this._group,value);}
    }

    private void SetProperty(ref SampleDataGroup sampleDataGroup, SampleDataGroup value)
    {
        throw new NotImplementedException();
    }

    public int intIsCustomNav { get; set; }           
}

/// <summary>
/// Wird aufgerufen, wenn auf ein Element innerhalb einer Gruppe geklickt wird.
/// </summary>
/// <param name="sender">GridView (oder ListView, wenn die Anwendung angedockt ist),
/// die das angeklickte Element anzeigt.</param>
/// <param name="e">Ereignisdaten, die das angeklickte Element beschreiben.</param>
void ItemView_ItemClick(object sender, ItemClickEventArgs e)
{
    // Navigate to the appropriate destination page, configuring the new page
    // by passing required information as a navigation parameter

    var group = (SampleDataGroup)e.ClickedItem;
    var groupId = group.UniqueId;

    var item = (SampleDataItem)e.ClickedItem;
    var itemId = item.UniqueId;


    int intGroup = Convert.ToInt32(group);

    // Abfrage Gruppe 1
    if (intGroup == 0)

        // Abfrage der Seiten
        if (item.intIsCustomNav == 0)
        {
            // Gruppe 1, Seite 1
            this.Frame.Navigate(typeof(ItemDetailPage), itemId);
        }

        if (item.intIsCustomNav == 1)
        {
            // Gruppe 1, Seite 2
            this.Frame.Navigate(typeof(ItemDetailPageA2), itemId);
        }

        // Abfrage Gruppe 2
        if (intGroup == 1)
        {
            // Abfrage der Seiten
            if (item.intIsCustomNav == 0)
            {
                // Gruppe 2, Seite 1
                this.Frame.Navigate(typeof(ItemDetailPageB1), itemId);
            }
        }

    }

You might do well to post an english translation of the exception. — Johnie Karr
In System.InvalidCastException an exception of type "AstroApp.exe" has occurred, but this was not handled in user code. Additional information: The object of type "AstroApp.Data.SampleDataItem can not be converted to type 'AstroApp.Data.SampleDataGroup ". — user3447311
you don't really need the translation, as it is a class cast exception. SampleDataItem can't be cast to SampleDataGroup. The runtime is telling you exactly what and where the problem is. An apple is not a banana. — John Gardner

drew_w drew_w · Accepted Answer · 2014-03-21T17:39:23

This is an invalid cast exception - in other words you are trying to use something that isn't of the type you expect. I noticed you are casting "ClickedItem" as both "SampleDataGroup" and as a "SampleDataItem". Unless there is some form of class inheritance going on here, this isn't possible. I would recommend you try the following code:

var group = e.ClickedItem as SampleDataGroup;
var groupId = group == null ? 0 : group.UniqueId;

var item = e.ClickedItem as SampleDataItem;
var itemId = item == null ? 0 : item.UniqueId;

I don't know if this is what you want but it will at least eliminate the error you are seeing. Hope that helps some!

EDIT & Another Issue:

I noticed that the next line after this error is:

// This won't work:
int intGroup = Convert.ToInt32(group);

This also doesn't look like it is going to work. I think you are going to want to learn more about strong types in .NET and how they work. Maybe the following MSDN page will get you started: http://msdn.microsoft.com/en-us/library/ms173104.aspx

C# App Grid Navigation - InvalidCastException

1 Answers