Wp7 ListBox ItemSource ObservableCollection IndexOUtofRange and Items are not updated

Question

I have the following issue: I am creating a Windows Phone 7 application and I am using a ListBox which is bound to an ObservableCollection people. The implementation of this you see below:

public class Person
{
    private string _id { get; set; }
    private string _name { get; set; }


    public Person(string Id, string Name, string Title)
    {
        _id = Id;
        _name = Name;
    }

    public string Id
    {

        get { return _id; }

        set
        {

            _id = value;

            FirePropertyChangedEvent("Id");

        }
    }

    public string Name
    {

        get { return _name; }

        set
        {

            _name = value;

            FirePropertyChangedEvent("Name");

        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void FirePropertyChangedEvent(string propertyName)
    {

        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));

    }

}

The people Collection is filled with Person objects. They are created in the following function... listValues is my ListBox.

void svc_GetHierachyCompleted(object sender, HCMobileSvc.GetHierachyCompletedEventArgs e)
    {
        var data = e.Result.ToArray();
        listValues.ItemsSource = null;
        people.Clear();

        int i = 0;
        foreach(var item in data)
        {
            if (i == 0)
            {
                // Manager
                mgrField1.Text = item[1].ToString();
                mgrField2.Text = item[2].ToString();
                i++;
            }
            else
            {
                // Untergebenen hinzufügen
                people.Add(new Person(item[0].ToString(), item[1].ToString(), item[2].ToString()));
            }

        }

        // Update List
        listValues.ItemsSource = people;

    }

Now I have a DataTemplate with two textblocks bound to both properties Id and Name. When the SelectionChanged event is fired I try to rebuild the entire list (so I call the function above again) using the following code:

            string id = people[listValues.SelectedIndex].Id;
        MessageBox.Show(id);
        CreateHierachy(id);

The CreateHierachy just only queries a WebService which then goes into the method above. The problem is, as soon as I select a value in the ListBox I get the following error:

ArgumentOutOfRangeException {"\r\nParameter name: index"}

The error is caused by the line listValues.SelectedIndex. I absolutely have no idea why that happens. What I know is that the MessageBox shows me the correct SelectedIndex value. What I also know is that when I remove the line people.Clear() that the error goes away but the ListBox does not get Updated.

Any ideas where the problem might be?

Thanks!!!

Bye, WorldSignia

Answer 1

You should check here for SelectedIndex being >= 0:

if (listValues.SelectedIndex >= 0)
     string id = people[listValues.SelectedIndex].Id;