fast way to find row selection state in datagridview

Question

I have a bound datagridview with about 1/2 a million records and may be sorted by any column. In the GUI user can select any number of rows (sometimes all of them with CTRL+A). From another source I get a large list of record IDs (up to 1000) and need to find out which of those IDs correspond to a selected row. I've tried many approaches, none of which perform fast enough. For instance:

Looping through the selected rows collection and looking for a match in the IDs list is out of the question because the SelectedRows count can be on the order of 1/2 million.

I also tried looping through the ID's list (which is typically on the order of 1000) and for each ID do a BindingSource.Find("Id", Value) which gives me the row index for each ID and I can then check if the Row is selected. This works fine if the grid is sorted by ID, but if it's not, the performance of Find() is too poor to be called 1000 times.

In short, i need a fast way to find the Row.Selected state for up to 1000 rows given the row object IDs. It seems the DataGridView or DataBinding should be able to handle this but it's not obvious how. Thanks in advance!

Only an untested comment. Bind Selected property and then search on the datatable. — paparazzo

EdFred EdFred · Accepted Answer · 2012-06-27T01:54:21

I would try the following:

If possible, use an ObservableCollection for the ItemsSource of the DataGridView.
Add a binding on the Selected property of the row to the underlying item contained in the ObservableCollection.
Use a CollectionViewSource and Filter

Here is a sample the does something very similar (although on much less data I suspect it will perform very well):

private ICollectionView _CarListView { get; set; }
private ObservableCollection<Car> _CarList;
public ObservableCollection CarList
{
    get
    {
        if (_CarList == null)
        {
            //Code to build the list

            //For the car filtering
            this._CarListView = CollectionViewSource.GetDefaultView(_CarList);
            this._CarListView.Filter = CarFilter;
        }
        return _CarList;
    }
}

private bool CarFilter(object item)
{
    Car car = item as Car;

    if(car.Name.Contains(FilterText))
    {
        return true;
    }
    else
    {
        return false;
    }
}

In your case, I would just tweak the CarFilter (which is really a Predicate<T>) so that you can look for the property that you bound to the Selected property in the DataGridViewRow. For example, you may create an IsSelected boolean on the object type contained in the ObservableCollection and just return where that item is true. Once you have that filtered list result, then run through the smaller list of ids you mentioned (around 1000 elements) and look where the ids match. I would try using a LINQ query against the two collections to perform that operation which should be about as fast you can get.

If all else fails, you could go back to your original looping technique and try the parallel library to do a Parallel.ForEach which will leverage your multi-core CPU to perform the operation faster. Although, I wouldn't brute force it. It seems like you have to make one pass to accumulate selected items from your large set and then look up each selected item in the smaller set.

fast way to find row selection state in datagridview

1 Answers