How to save selected rows in a DataGridView when the mouse is held in a cell?

Question

I am trying to implement row moving in a DataGridView. I want to be able to select multiple rows and click on any of the selected row cells to start the drag and drop operation. The problem is that the rows become inaccessible when I hold the mouse in the cell. How can I prevent this?

Answer 1

From a quick Google search, this seems like a solution for custom drag and drop. Note. I just tore the following code from the linked page, I cannot vouch for its effectiveness.

private Rectangle dragBoxFromMouseDown;
private int rowIndexFromMouseDown;
private int rowIndexOfItemUnderMouseToDrop;

private void dataGridView1_MouseMove(object sender, MouseEventArgs e)
{
    if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
    {
        // If the mouse moves outside the rectangle, start the drag.
        if (dragBoxFromMouseDown != Rectangle.Empty &&
            !dragBoxFromMouseDown.Contains(e.X, e.Y))
        {
            // Proceed with the drag and drop, passing in the list item.                    
            DragDropEffects dropEffect = dataGridView1.DoDragDrop(dataGridView1.Rows[rowIndexFromMouseDown], DragDropEffects.Move);
        }
    }
}

private void dataGridView1_MouseDown(object sender, MouseEventArgs e)
{
    // Get the index of the item the mouse is below.
    rowIndexFromMouseDown = dataGridView1.HitTest(e.X, e.Y).RowIndex;

    if (rowIndexFromMouseDown != -1)
    {
        // Remember the point where the mouse down occurred. 
        // The DragSize indicates the size that the mouse can move 
        // before a drag event should be started.                
        Size dragSize = SystemInformation.DragSize;
        // Create a rectangle using the DragSize, with the mouse position being
        // at the center of the rectangle.
        dragBoxFromMouseDown = new Rectangle(new Point(e.X - (dragSize.Width / 2), e.Y - (dragSize.Height / 2)), dragSize);
    }
    else
    {
        // Reset the rectangle if the mouse is not over an item in the ListBox.
        dragBoxFromMouseDown = Rectangle.Empty;
    }
}

private void dataGridView1_DragOver(object sender, DragEventArgs e)
{
    e.Effect = DragDropEffects.Move;
}

private void dataGridView1_DragDrop(object sender, DragEventArgs e)
{
    // The mouse locations are relative to the screen, so they must be 
    // converted to client coordinates.
    Point clientPoint = dataGridView1.PointToClient(new Point(e.X, e.Y));
    // Get the row index of the item the mouse is below. 
    rowIndexOfItemUnderMouseToDrop = dataGridView1.HitTest(clientPoint.X, clientPoint.Y).RowIndex;
    // If the drag operation was a move then remove and insert the row.
    if (e.Effect== DragDropEffects.Move)
    {
        DataGridViewRow rowToMove = e.Data.GetData(typeof(DataGridViewRow)) as DataGridViewRow;
        dataGridView1.Rows.RemoveAt(rowIndexFromMouseDown);
        dataGridView1.Rows.Insert(rowIndexOfItemUnderMouseToDrop, rowToMove);
    }
}

Answer 2

The datagridview subclass will help you do this conditionally:

class SimpleDataGridView : DataGridView {

    public Action<DataGridViewCellMouseEventArgs> BeforeCellMouseDown;
    public Action<DataGridViewCellMouseEventArgs> AfterCellMouseDown;

    protected override void OnCellMouseDown(DataGridViewCellMouseEventArgs e) {
        if(BeforeCellMouseDown != null)
            BeforeCellMouseDown(e);

        base.OnCellMouseDown(e);

        if(AfterCellMouseDown != null)
            AfterCellMouseDown(e);
    }
}

Then you can use it this way in your constructor:

IEnumerable<DataGridViewRow> sel = null;

dataGridView1.BeforeCellMouseDown = 
    e => {
        if (yourCondition)
            // Save the selection
            sel = dataGridView1.SelectedRows.OfType<DataGridViewRow>();
        else
            sel = null;
    };

dataGridView1.AfterCellMouseDown = 
    e => {
        if(sel != null) {
            // Restore the selection
            foreach(var row in sel)
                row.Selected = true;
        }
    };

Answer 3

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