Focus on first item of first LongListSelector within a Pivot

Question

I have a report to fill in that is made up of a List of sections, each of which has a List of questions. My current implementation uses a Pivot control whose ItemsSource is set to the List of sections and DataTemplate is a LongListSelector whose ItemsSource is set to the List of questions.

When the user attempts to submit the report, I loop through all the questions to check their validity. If any come back invalid, a flag is set and an error message is shown next to that question.

I would like to be able to focus on the first question that has that flag set but cannot figure out how to obtain a reference to the required LongListSelector so that I can call it's ScrollTo method.

Code:

View

<phone:Pivot toolkit:TurnstileFeatherEffect.FeatheringIndex="0"
                 Name="QuestionPivot"
                 ItemsSource="{Binding Sections, Mode=TwoWay}">
        <phone:Pivot.Title>
            <TextBlock>
                <Run Text="{Binding Path=LocalizedResources.ApplicationTitle, Source={StaticResource LocalizedStrings}}"/>
                <Run Text=" "/>
                <Run Text="{Binding Path=LocalizedResources.DailyReport, Source={StaticResource LocalizedStrings}}"/>
                <Run Text=" - "/>
                <Run Text="{Binding ProjectName}"/>
            </TextBlock>
        </phone:Pivot.Title>            
        <phone:Pivot.HeaderTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding SectionName}"/>
            </DataTemplate>
        </phone:Pivot.HeaderTemplate>
        <phone:Pivot.ItemTemplate>
            <DataTemplate>
                <phone:LongListSelector ItemsSource="{Binding Questions, Mode=TwoWay}">
                    <phone:LongListSelector.ItemTemplate>
                        <DataTemplate>
                            <StackPanel Margin="0 0 0 20">
                                ...  
                            </StackPanel>
                        </DataTemplate>
                    </phone:LongListSelector.ItemTemplate>
                </phone:LongListSelector>
            </DataTemplate>
        </phone:Pivot.ItemTemplate>

    </phone:Pivot>

Code Behind (including my failed attempt to cast the SelectedItem to a LongListSelector...)

    private void FocusOnFirstInvalid(object sender, EventArgs e)
    {
        int selectedItem = 1;
        foreach (ReportDraftSection s in QuestionPivot.Items)
        {
            foreach(ReportQuestion q in s.Questions)
            {
                if(q.IsNotValid)
                {
                    QuestionPivot.SelectedIndex = selectedItem;
                    var l = (LongListSelector)QuestionPivot.SelectedItem;
                    l.ScrollTo(q);
                }
            }
            selectedItem += 1;
        }
    }

Any help would be greatly appreciated.

Answer 1

Since Pivot's ItemsSource is a List of Section, QuestionPivot.SelectedItem contains a Section object instead of LongListSelector. You can try to use ItemContainerGenerator to get PivotItem from SelectedItem, then get LongListSelector from PivotItem's Content (not tested yet) :

.......
QuestionPivot.SelectedIndex = selectedItem;
var pivotItem = (PivotItem)QuestionPivot
                .ItemContainerGenerator
                .ContainerFromItem(QuestionPivot.SelectedItem);
var l = (LongListSelector)pivotItem.Content;
l.ScrollTo(q);
.......