Scroll WPF DataGrid to show selected item on top

Question

I have a DataGrid with many items and I need to programmatically scroll to the SelectedItem. I have searched on StackOverflow and Google, and it seems the solution is ScrollIntoView, as follows:

grid.ScrollIntoView(grid.SelectedItem)

which scrolls the DataGrid up or down until the selected item is in focus. However, depending on the current scroll position relative to the selected item, the selected item may end up being the last visible item in the DataGrid's ScrollViewer. I want that the selected item will be the first visible item in the ScrollViewer (assuming there are enough rows in the DataGrid to allow this). So I tried this:

'FindVisualChild is a custom extension method that searches in the visual tree and returns 
'the first element of the specified type
Dim sv = grid.FindVisualChild(Of ScrollViewer)
If sv IsNot Nothing Then sv.ScrollToEnd()
grid.ScrollIntoView(grid.SelectedItem)

First I scroll to the end of the DataGrid and only then do I scroll to the SelectedItem, at which point the SelectedItem is shown at the top of the DataGrid.

My problem is that scrolling to the end of the DataGrid works well, but subsequently scrolling to the selected item doesn't always work.

How can I resolve this issue, or is there any other alternative strategy for scrolling to a specific record in the top position?

Answer 1

The accepted answer to this other question shows a different approach to get the first/last visible row of such a grid. You could find out the index of your row and directly scroll there or scroll down row by row until the first visible row matches.

Answer 2

You were on the right track, just try to work with collection view instead of working directly on the datagrid for this kind of needs.

Here is a working example where the desired item is always displayed as first selected item if possible, otherwise the scrollviewer is scrolled to the end and the target item is selected at its position.

The key points are :

• Use CollectionView on the business side and enable current item synch on the XAML control (IsSynchronizedWithCurrentItem=true)
• Defer the "real" target scroll in order to allow the "Select Last item" to be visualy executed (By using a Dispatcher.BeginInvoke with a low priority)

Here is the business logic (This is automatic convertion from C# to VB)

Public Class Foo

    Public Property FooNumber As Integer
        Get
        End Get
        Set
        End Set
    End Property
End Class

Public Class MainWindow
    Inherits Window
    Implements INotifyPropertyChanged

    Private _myCollectionView As ICollectionView

    Public Sub New()
        MyBase.New
        DataContext = Me
        InitializeComponent
        MyCollection = New ObservableCollection(Of Foo)
        MyCollectionView = CollectionViewSource.GetDefaultView(MyCollection)
        Dim i As Integer = 0
        Do While (i < 50)
            MyCollection.Add(New Foo)
            i = (i + 1)
        Loop

    End Sub

    Public Property MyCollectionView As ICollectionView
        Get
            Return Me._myCollectionView
        End Get
        Set
            Me._myCollectionView = value
            Me.OnPropertyChanged("MyCollectionView")
        End Set
    End Property

    Private Property MyCollection As ObservableCollection(Of Foo)
        Get
        End Get
        Set
        End Set
    End Property

    Private Sub ButtonBase_OnClick(ByVal sender As Object, ByVal e As RoutedEventArgs)
        Dim targetNum As Integer = Convert.ToInt32(targetScroll.Text)
        Dim targetObj As Foo = Me.MyCollection.FirstOrDefault(() => {  }, (r.FooNumber = targetNum))

        'THIS IS WHERE THE MAGIC HAPPENS
        If (Not (targetObj) Is Nothing) Then
            'Move to the collection view to the last item
            Me.MyCollectionView.MoveCurrentToLast
            'Bring this last item into the view
            Dim current = Me.MyCollectionView.CurrentItem
            itemsContainer.ScrollIntoView(current)
            'This is the trick : Invoking the real target item select with a low priority allows previous visual change (scroll to the last item) to be executed
            Dispatcher.BeginInvoke(DispatcherPriority.ContextIdle, New Action(() => {  }, Me.ScrollToTarget(targetObj)))
        End If

    End Sub

    Private Sub ScrollToTarget(ByVal targetObj As Foo)
        Me.MyCollectionView.MoveCurrentTo(targetObj)
        itemsContainer.ScrollIntoView(targetObj)
    End Sub

    Public Event PropertyChanged As PropertyChangedEventHandler

    Protected Overridable Sub OnPropertyChanged(ByVal propertyName As String)
        If (Not (PropertyChanged) Is Nothing) Then
            PropertyChanged?.Invoke(Me, New PropertyChangedEventArgs(propertyName))
        End If

    End Sub
End Class

And this is the xaml

 <Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <DataGrid x:Name="itemsContainer" ItemsSource="{Binding MyCollectionView}" IsSynchronizedWithCurrentItem="True"  Margin="2" AutoGenerateColumns="False" >
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding FooNumber}"></DataGridTextColumn>
        </DataGrid.Columns>
    </DataGrid>

    <StackPanel Grid.Column="1">
        <TextBox x:Name="targetScroll" Text="2" Margin="2"></TextBox>
        <Button Content="Scroll To item" Click="ButtonBase_OnClick" Margin="2"></Button>
    </StackPanel>
</Grid>

Answer 3

I Solved this question with following code:

public partial class MainWindow:Window
{
    private ObservableCollection<Product> products=new ObservableCollection<Product> ();

    public MainWindow()
    {
        InitializeComponent ();

        for (int i = 0;i < 50;i++)
        {
            Product p=new Product { Name="Product "+i.ToString () };
            products.Add (p);
        }

        lstProduct.ItemsSource=products;
    }

    private void lstProduct_SelectionChanged(object sender,SelectionChangedEventArgs e)
    {
        products.Move (lstProduct.SelectedIndex,0);
        lstProduct.ScrollIntoView (lstProduct.SelectedItem);
    }
}

public class Product
{
    public string Name { get; set; }
}


<Grid>
    <ListBox Name="lstProduct" Margin="20" DisplayMemberPath="Name" SelectionChanged="lstProduct_SelectionChanged" />
</Grid>