Question

I am having an issue with my ListPicker control. I have implemented my listpicker in my page as follows but I am receiving an IndexOutOfRangeException upon runtime, and I am not quite sure of how to fix the problem:

SettingsPage.xaml

<phone:PhoneApplicationPage.Resources>
    <DataTemplate x:Name="SearchProviderItemTemplate">
        <TextBlock Text="{Binding SearchProvider}" />
    </DataTemplate>
</phone:PhoneApplicationPage.Resources>

<ScrollViewer x:Name="ContentPanel_Browser" Margin="12,0,12,0">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto"/>
                        <RowDefinition Height="70"/>
                        <RowDefinition Height="70"/>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>

                    ...

                    <!-- Search Provider -->
                    <TextBlock Text="Search provider" Margin="12,7,12,8"
                       Grid.Row="3" VerticalAlignment="Bottom"
                       Foreground="{StaticResource PhoneSubtleBrush}"/>
                    <toolkit:ListPicker x:Name="SearchProviderListPicker" Grid.Row="4" Grid.ColumnSpan="2" Margin="12,0,12,0"  
                                        ItemTemplate="{Binding SearchProviderItemTemplate}" 
                                        SelectionChanged="SearchProviderListPicker_SelectionChanged" />
                </Grid>
            </ScrollViewer>                

SettingsPage.xaml.cs

    string searchProvider;

    String[] SearchProvider = 
    {
        "Google", 
        "Bing",
        "Yahoo",
        "Ask",
        "AOL"
    };

    private void SearchProviderListPicker_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        string selectedItem = e.AddedItems[0] as string;  //IndexOutOfRangeException was unhandled

        switch (selectedItem)
        {
            case "Google":
                searchProvider = "http://www.google.com/search?q=";
                break;
            case "Bing":
                searchProvider = "http://www.bing.com/search?q=";
                break;
            case "Yahoo":
                searchProvider = "http://search.yahoo.com/search?p=";
                break;
            case "Ask":
                searchProvider = "http://www.ask.com/web?q=";
                break;
            case "AOL":
                searchProvider = "http://search.aol.com/search?q=";
                break;
            //default:
            //    SearchProvider = "http://search.aol.com/search?q=";
            //    break;
        }

The IndexOutOfRangeException occurs with line ‘string selectedItem = e.AddedItems[0] as string;’ in SettingsPage.xaml.cs. I remember seeing how to solve this somewhere on StackOverflow but I cannot find that source now. Any idea on how to set the bounds or check to ensure this exception will not occur? Thanks in advance (any code assistance would help I am new to this!).

Answer 1

As AddedItems is an IList, can you not just make a check that it has some items in it before you try and access them?

Something like the following at the top of the method should solve the problem:

if (e.AddedItems.Count <= 0)
{
    return;
}