按enter键时将焦点设置为DataGridTemplateColumn子控件

<DataGrid ItemsSource="{Binding Data}" IsReadOnly="False">
    <DataGrid.Columns>
        <DataGridTemplateColumn>
            <DataGridTemplateColumn.CellEditingTemplate>
                <DataTemplate>
                    <TextBox KeyDown="TextBox_KeyDown" Text="{Binding Value}" />
                </DataTemplate>
            </DataGridTemplateColumn.CellEditingTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

private void TextBox_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Enter)
    {
        TextBox textBox = (TextBox)sender;
        DataGridCell cell = FindVisualParent<DataGridCell>(textBox);
        DataGridRow row = FindVisualParent<DataGridRow>(cell);
        DataGrid dataGrid = FindVisualParent<DataGrid>(row);

        int columnIndex = dataGrid.Columns.IndexOf(cell.Column);
        int rowIndex = dataGrid.Items.IndexOf(row.Item);

        if (rowIndex < dataGrid.Items.Count - 1)
        {
            DataGridRow nextRow = dataGrid.ItemContainerGenerator.ContainerFromIndex(rowIndex + 1) as DataGridRow;
            DataGridCell nextCell = dataGrid.Columns[columnIndex].GetCellContent(nextRow).Parent as DataGridCell;
            TextBox nextTextBox = FindVisualChild<TextBox>(nextCell);

            if (nextTextBox != null)
            {
                Keyboard.Focus(nextTextBox);
            }
        }
    }
}

private T FindVisualParent<T>(DependencyObject child) where T : DependencyObject
{
    DependencyObject parent = VisualTreeHelper.GetParent(child);

    if (parent == null)
        return null;

    T parentT = parent as T;
    return parentT ?? FindVisualParent<T>(parent);
}

private T FindVisualChild<T>(DependencyObject parent) where T : DependencyObject
{
    int childCount = VisualTreeHelper.GetChildrenCount(parent);

    for (int i = 0; i < childCount; i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(parent, i);

        T childT = child as T;
        if (childT != null)
            return childT;

        T foundChild = FindVisualChild<T>(child);
        if (foundChild != null)
            return foundChild;
    }

    return null;
}