Scroll to selected item

[vrykov]

Hello,

first of all, Xamarin.Forms.DataGrid is a great thing, thanks!

I'm struggling with making an element visible. Here's my scenario:
I have a long collection of items. When I set SelectedItem in viewmodel, DataGrid selects that item.
However, if newly selected item wasn't visible before, DataGrid does not scroll to make it visible.

In ListView there is a ScrollTo method with does excatly what I want, for example:

listView.ScrollTo(vm.ItemsCollection.LastOrDefault(), ScrollToPosition.Start, false);

Is this possible with Xamarin.Forms.DataGrid?

[akgulebubekir]

Hi, such a feature not exists for now, but would be nice to implement. Will implement when i have free time

[vrykov]

Thanks! Really looking forward.

Possible implementation in DataGrid.xaml.cs:

    public void ScrollTo(object item, ScrollToPosition position, bool animated)
    {
        _listView.ScrollTo(item, position, animated);
    }

    public void ScrollTo(object item, object group, ScrollToPosition position, bool animated)
    {
        _listView.ScrollTo(item, group, position, animated);
    }

Then methods can be easily used from codebehind in ItemSelected event handlers:

    private void DataGrid_ItemSelected(object sender, SelectedItemChangedEventArgs e)
    {
        var dg = (Xamarin.Forms.DataGrid)sender;
        dg.ScrollTo(e.SelectedItem, ScrollToPosition.Start, false);
    }

(Not tested yet)

[vrykov]

If someone is interested, here's some dirty workaround:

1. Add this class to your project

using System.Reflection;
using Xamarin.Forms;
using System.Linq;

class DataGridListViewCachingUtil
{
    private ListView _listView;
    public ListView GetListView(Xamarin.Forms.DataGrid.DataGrid grid)
    {
        if (_listView == null)
        {
            var gridType = typeof(Xamarin.Forms.DataGrid.DataGrid);

            FieldInfo[] fields = gridType.GetFields(
                         BindingFlags.NonPublic |
                         BindingFlags.Instance);

            var _lv = fields.FirstOrDefault(i => i.Name == "_listView");
            if (_lv != null)
            {
                _listView = (ListView)_lv.GetValue(grid);
            }
        }

        return _listView;
    }

    public ListView GetListView(object sender)
    {
        return GetListView((Xamarin.Forms.DataGrid.DataGrid)sender);
    }
}

2. This is an example showing how listview can be accessed from codebehind:

    private void DataGrid_ItemSelected(object sender, SelectedItemChangedEventArgs e)
    {
        if(e.SelectedItemIndex != -1)
        {
            var listView = cachingUtil.GetListView(sender);
            if (listView != null)
                listView.ScrollTo(e.SelectedItem, ScrollToPosition.Start, false);
        }
    }
   

ListView object is cached within the utility class.
Works for me if DataGrid is visible.