How to make 2 threads work on one panel in winform c#?

Question

I am trying to make two threads work at the same time on the same panel in a windows form, the threads are the same. I have looked for answers already but no question treated this thing (at least from what i saw). here is the code :

The code in the form.cs :

semaphore = new Semaphore();



    p1t1 = new PanelThread(new Point(10, 10),
                         150, Direction.West, Track.track1, pnl1, typetrain.loco,
                         Color.Blue,
                         semaphore
                         );



    p2t2 = new PanelThread(new Point(390, 390),
                         150, Direction.East, Track.track2, panel5, typetrain.loco,
                         Color.Red,
                         semaphore
                         );

    green1t1 = new PanelThread(new Point(10, 10),
                         150, Direction.North, Track.track1, pnl1, typetrain.wagon,
                         Color.Green,
                         semaphore
                         );


    semThread = new Thread(new ThreadStart(semaphore.Start));

    thread1 = new Thread(new ThreadStart(p1t1.Start));

    thread2 = new Thread(new ThreadStart(p2t2.Start));

    thread3 = new Thread(new ThreadStart(green1t1.Start));

    this.Closing += new CancelEventHandler(this.Form1_Closing);

    semThread.Start();
    thread1.Start();
    thread2.Start();
    thread3.Start();

the code in the panelthread.cs :

public PanelThread(Point origin,
                       int delay,
                       Direction direction,
                       Track track,
                       Panel panel,
                       typetrain locwag,
                       Color colour,
                       Semaphore semaphore)
    {
        this.origin = origin;
        this.delay = delay;
        this.direction = direction;
        this.panel = panel;
        this.colour = colour;
        this.plane = origin;
        this.panel.Paint += new PaintEventHandler(this.panel_Paint);
        this.track = track;
        this.locwag = locwag;
        switch (this.direction)
        {
            case Direction.East:
                this.xDelta = -10;
                this.yDelta = 0;
                break;

            case Direction.West:
                this.xDelta = +10;
                this.yDelta = 0;
                break;

            case Direction.North:
                this.xDelta = 0;
                this.yDelta = -10;
                break;

            case Direction.South:
                this.xDelta = 0;
                this.yDelta = +10;
                break;
        }


        this.semaphore = semaphore;
    }

When I launch the program, the program bugs at the paint event handler with an System.ArgumentException at the line g.FillRectangle:

private void panel_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;

    SolidBrush brush = new SolidBrush(colour);
    g.FillRectangle(brush, plane.X, plane.Y, 10, 10);

    brush.Dispose();    //  Dispose of graphic
    g.Dispose();        //  resources  
}

UPDATE : I have tried using invoke in the panelthread.cs like this :

if (this.panel.InvokeRequired)
    {
        this.panel.Invoke((MethodInvoker)delegate { this.panel.Paint += new PaintEventHandler(this.panel_Paint); });
    }

I don't have any error now, but the squares are not being created, so i don't go at all in the panel_paint function. I surely have written something wrong in the Invoke calling, or I wrote it in the wrong place.

Please don't post code as screen shots, but paste the relevant code as text in your question. This makes it easier for us to reproduce a problem, and to use it in answers and for others to search. To your problem: you should not access UI elements from different threads. Access to UI elements should be synchronized on the UI thread that created the UI element. Look for `Control.Invoke` or `Control.BeginInvoke` to invoke an action on the UI thread. — René Vogt, Mar 30 '17 at 13:44
Maybe this helps you: https://stackoverflow.com/questions/142003/cross-thread-operation-not-valid-control-accessed-from-a-thread-other-than-the?rq=1 — René Vogt, Mar 30 '17 at 13:46
thanks for the answer, I used screens because I thought the code would be too big, I will keep it in mind for the future — raiskader, Mar 30 '17 at 13:47
I tried using invoke, but the code gets blocked, I added more detail in the question — raiskader, Mar 30 '17 at 15:00
The paint event (and actual painting) will always have to be in the UI thread. There's no reason to try to put that into a thread as it will always just require a invoke back to the main thread every time it is called. — David, Mar 30 '17 at 16:17

score 0 · Accepted Answer · answered Apr 03 '17 at 08:55

0

I actually found the error, and having found that the panel_paint is actually always on the main thread, the error was somewhere else. In the end, I saw that I only needed to take out the g.dispose command in panel_paint, as it destroyed the graphic before painted the next object.

answered Apr 03 '17 at 08:55

raiskader

89
4
16

Thank you for coming back with a solution to your own problem! Now that you've solved it, you can also choose to delete your question if you think there's no use in keeping it around. – PJvG Apr 03 '17 at 08:58

How to make 2 threads work on one panel in winform c#?

1 Answers1