Paint event keeps firing

Question

I've been working on drawing a grid in C#, which works! But somehow I keep running into some problems with the method DrawGrid. I found that it is being redrawn every time a label gets added, and continuously after that. Here is my code:

Rectangle[,] rec = new Rectangle[6,6];
Label label_1 = new Label();
Label label_2 = new Label();

public Reversi()
        {
            ClientSize = new Size(500,425);
            BackColor = Color.DarkGreen;
            NewGame();
            Paint += DrawGrid;
        }

public void NewGame()
        {
            // here is some more stuff which I will leave out for the sake of clarity
            for (int i = 0; i < grspel; i++)
            {
                for (int j = 0; j < grspel; j++)
                {
                    rec[i, j] = new Rectangle(50 + i * 50, 100 + j * 50, 50, 50);
                }
            }
            DrawLabels();
        }

public void DrawLabels()
        {
            label_1.Location = new Point(20, 50);
            label_1.Text = "Zwart: " + zwart;
            Controls.Add(label_1);

            label_2.Location = new Point(330, 50);
            label_2.Text = "Wit: " + wit;
            Controls.Add(label_2);
        }

public void DrawGrid(object o, PaintEventArgs pea)
        {
            MessageBox.Show("test");
            for (int i = 0; i < 6; i++)
            {
                for (int j = 0; j < 6; j++)
                {
                    pea.Graphics.DrawRectangle(new Pen(Brushes.Black), rec[i,j]);
                }
            }
        }

To visualize my problem I placed MessageBox.Show("test"); at the start of my DrawGrid method. The rest of my code (which is not on here) uses this method and is not working properly. I've narrowed the problem down to this.
Getting rid of the Controls.Add(label_i) fixes the problem, but I need the labels. Why does this happen and more importantly, how can I fix it?

Create a copy of your project and make it a [mre] so we can reproduce it. If I get code that I can run, I will typically provide code that fixes it. If I don't get code which compiles, I can't give you code back. — Thomas Weller, Oct 22 '21 at 09:41

Thomas Weller · Answer 1 · 2021-10-22T09:44:30.253

You add a label, thus there's an event that UI changes and needs to repaint. It should paint the added label, right? IMHO that's expected.

You don't need to add the labels to the list of controls each time. Just add them once (e.g. in Form.Load).

However, changing the position of the label will likely also require a repaint. It should paint the label at the new position, right? But your position is constant as well. Just set the position once.

Repainting is normal and good, because it keeps the contents updated. It shouldn't be a problem. So, why don't you like it? Probably it causes flickering and you don't like that.

Showing a MessageBox might not be a good idea either. If the MessageBox is in front of your form, the part that is behind the MessageBox will need to be painted again.

You can

use SuspendLayout() to tell the painter that it's not worth reacting to changes immediately, but wait until you finished making all layout related changes. Use ResumeLayout() to tell the painter it's time to paint now.
check out options for double buffering

but I need the labels

Actually you don't. You can use Graphics.DrawString() instead of using a label.

Paint event keeps firing

1 Answers1