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Why is removing rows in DataGridView so slow?

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Pete Moss

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Aug 2, 2007, 10:02:07 AM8/2/07

I have a DataGridView with VirtualMode = true. The performance is great for
displaying many thousands of rows. However, if I remove a block of rows in
the middle of the grid, it takes multiple seconds while the scroll bar moves
around a lot, then the rows below finally get repainted. If I add the same
block of rows back in, performance is fine. The added rows appear almost
immediately.

The problem seems to be worse as I move farther down in the row set.

I tried 2 approaches to removing these rows. First, I simple decrement the
RowCount by the number of rows I want to remove. The 2nd approach was to do
this:

for (int n = nStart; n < nStart + count; n++)
grid.Rows.RemoveAt(n);

Same performance. In fact, when I use Reflector to see what RemoveAt() is
doing, it looks like it just decrements the RowCount.

Why should it be so slow? Is there anything I can do to speed this up?

Pete Moss

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Aug 4, 2007, 2:54:01 PM8/4/07

In doing some more on line trolling, I found a solution on a blog post. The
answer is clear all the Rows, then set the RowCount to what I want. Here is
what I can do to remove a bunch of records from deleteStart to deleteStart +
count:

// Cache the first visible cell because when we clear the rows, we would
lose our scroll position
DataGridViewCell cell = grid.FirstDisplayedCell;
int firstVisibleColIndex = cell.ColumnIndex;
int firstVisibleRowIndex = cell.RowIndex;

// New RowCount after I remove the block of Rows
int rowCount = grid.RowCount - count;

grid.Rows.Clear();
grid.RowCount = rowCount;

cell = grid[firstVisibleColIndex, firstVisibleRowIndex];
grid.FirstDisplayedCell = cell;

Works great! And it happens essentially instantaneously. Note that the above
code is display only. I didn't show you the BL that describes how I remove
the rows from my underlying datastore, but that code executes in almost no
time anyway so that was not my issue.

kristywinters

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Nov 12, 2009, 12:11:11 PM11/12/09

I had this issue as well, but found an easier way to resolve it. Just switch to RemoveAt, its instant and much cleaner.

Old code:

foreach (DataGridViewRow dgvRow in dgvDevices.SelectedRows)
dgvDevices.Rows.Remove(dgvRow);

New code:

foreach (DataGridViewRow dgvRow in dgvDevices.SelectedRows)
dgvDevices.Rows.RemoveAt(dgvRow.Index);

The remove used to take forever, but now its instant.

PeteMos wrote:

In doing some more on line trolling, I found a solution on a blog post.