how do I use Graphics.DrawLine with Panel-Controls

@Jayraj Chhaya

your provided code does not work in many ways. you neglect the Device'Panels child panels. the lines might by drawn but the childpanels will override the lines. Another issue is the fact that your DevicePanel does not do DockStyle.Fill, its location is 0/0 instead of 0/menustrip.height, thus from the first row panels part is cut.

instead of class DevicePanel I've added a UserControl but that does not work too.

To draw horizontal lines between rows of panels in a WinForms application, you need to handle the drawing logic correctly. One approach is to override the OnPaint method of the DevicePanel control and draw the lines there

using System.Drawing;
using System.Windows.Forms;

public class DevicePanel : Panel
{
    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        
        using (var pen = new Pen(Color.Black))
        {
            int panelWidth = this.Width / 4; // Assuming 4 panels per row
            int rowCount = this.Controls.Count / 4; // Calculate the number of rows
            
            for (int i = 1; i < rowCount; i++)
            {
                int y = i * panelWidth;
                e.Graphics.DrawLine(pen, 0, y, this.Width, y);
            }
        }
    }
}

By overriding the OnPaint method of the DevicePanel control, you can draw the horizontal lines between rows based on the number of panels dynamically. This ensures that the lines are drawn correctly when the control is painted.