Does the Windows Forms DataGridView implement a true virtual mode?

Question

I have a SQL table containing currently 1 million rows that will grow over time.

There is a specific user requirement to present a sortable grid that displays all rows without paging. The user expects to be able to very quickly jump from row to row and top to bottom by using the scrollbar.

I am familiar with "virtual mode" grids that only present a visible subset of the overall data. They can provide excellent UI performance and minimal memory requirements, (I've even implemented an application using this technique many years ago).

The Windows Forms DataGridView provides a virtual mode that looks like it should be the answer. However unlike other virtual modes I've encountered, it still allocates memory for every row (confirmed in ProcessExplorer). Obviously this causes overall memory usage to needlessly greatly increase and, while allocating these rows, there is a noticeable delay. Scrolling performance also suffers on 1 million + rows.

A real virtual mode would have no need to allocate any memory for rows not being displayed. You just give it the total row count (eg 1,000,000) and all the grid does is scale the scrollbar accordingly. When it is first displayed the grid simply asks for data the first n (say 30) visible rows only, instantaneous display.

When the user scrolls the grid, a simple row offset and the number of visible rows are provided and can be used to retrieve data from the data store.

Here's an example of the DataGridView code I'm currently using:

public void AddVirtualRows(int rowCount)
{
    dataGridList.ColumnCount = 4;


    dataGridList.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.None;
    dataGridList.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.None;

    dataGridList.VirtualMode = true;

    dataGridList.RowCount = rowCount;

    dataGridList.CellValueNeeded += new DataGridViewCellValueEventHandler(dataGridList_CellValueNeeded);


}
void dataGridList_CellValueNeeded(object sender, DataGridViewCellValueEventArgs e)
{
    e.Value = e.RowIndex;
}

Am I missing anything here, or is the "virtual" mode of the DataGridView not really virtual at all?

[Update]

It looks like the good old ListView implements exactly the sort of virtual mode I'm looking for. But unfortunately the ListView does not have the cell formatting capabilities of the DataGridView, so I can't use it.

For others that might be able to, I tested it with a four column ListView (in Detail mode), VirtualMode= True and VirtualListSize =100,000,000 rows.

The list is displayed immediately with the first 30 rows visible. I can then scroll rapidly to the bottom of the list with no delay. The memory usage is constant 10 MB at all times.

Answer 1

Check out these articles (if you haven't already):

How to: Implement Virtual Mode in the Windows Forms DataGridView Control

Paging Data with DataGridView in VirtualMode