Draw marks on a DataGridView vertical Scrollbar

Question

I am working on a project where cells in a DataGridView get highlighted. And I was wondering if I can make marks on the scrollbar itself to indicate where those highlights are. Any ideas may be helpful.

Answer 1

The Yes, the No and a Maybe

The Yes: According to this it is possible. However, this is a links only answer; not sure where that will lead..

The No: According to Cody Gray's excellent analysis in his answer to this post painting on a scrollbar is not possible.

But Maybe a workaround will solve your problem..?

Here is the idea:

You add a thin Panel that either overlays the scrollbar or attaches itself to its left. I should be really thin and go over the height of the scrolbar; it gets redrawn with the usual Paint events.

You keep a List of Rows, for which marks should be shown. This List is re-created or maintained upon:

• adding & removing Rows
• changing your target row
• possibly when sorting or Filtering

Here is a little code, just a quick proof of concept. For a more robust solution I guess I would create a decorator class to which the DataGridView would register.

Now, when you move the lift towards the marks you will find the target rows. A lot of room for improvement, but a start imo..

You have to change the isRowMarked() function to your needs. I have chosen to test the first Cell's Backcolor..

You can also easily use different colors for different marks; maybe by copying them from the marked row/cell.

public Form1()
{
    InitializeComponent();

    dataGridView1.Controls.Add(indicatorPanel);
    indicatorPanel.Width = 6;
    indicatorPanel.Height = dataGridView1.ClientSize.Height - 39;
    indicatorPanel.Top = 20;
    indicatorPanel.Left = dataGridView1.ClientSize.Width - 21;
    indicatorPanel.Paint += indicatorPanel_Paint;
    dataGridView1.Paint += dataGridView1_Paint;
}

Panel indicatorPanel = new Panel();
List<DataGridViewRow> tgtRows = new List<DataGridViewRow>();

void dataGridView1_Paint(object sender, PaintEventArgs e)
{
    indicatorPanel.Invalidate();
}

void indicatorPanel_Paint(object sender, PaintEventArgs e)
{   // check if there is a HScrollbar
    int hs = ((dataGridView1.ScrollBars & ScrollBars.Vertical) != ScrollBars.None ? 20 : 0);

    e.Graphics.FillRectangle(Brushes.Silver, indicatorPanel.ClientRectangle);
    foreach (DataGridViewRow tRow in tgtRows)
    {
        int h = (int)(1f * (indicatorPanel.Height - 20 + hs) * tRow.Index 
                         / dataGridView1.Rows.Count);
        e.Graphics.FillRectangle(Brushes.Red, 0, h-3, 6, 4);
    }
}

bool isRowMarked(DataGridViewRow row)
{
    return row.Cells[0].Style.BackColor == Color.Red;  // <<-- change!
}

// call in: dataGridView1_RowsRemoved, dataGridView1_RowsAdded
// also whenever you set or change markings and after sorting or a filtering
void findMarkers()
{
    tgtRows.Clear();
    foreach (DataGridViewRow row in dataGridView1.Rows)
        if (isRowMarked(row) ) tgtRows.Add(row); 
    indicatorPanel.Invalidate();
}

Note I have removed the first answer as the original requirements talk of 'marks' not just 'a few marks'. The second version seems a lot nicer to me, now.