Problem with Windows.Forms.Timer and menu items interaction

Question

I would like help with a problem I'm having with System.Windows.Forms.Timer and menu item interactions. In the designer I have dragged in a Windows.Forms.Timer, which I use in a Game of Life implementation to determine when to switch to the next generation. I have menu subitems called Start, Stop, Pause, and Resume. I use the Start menu item to start the timer going. I wish to use Pause to temporarily stop the timer, Resume to resume running the timer, and Stop when I am done with the timer. The problem is: After I start the timer running, the UI no longer responds to the menu item events to Stop, Pause, or Resume. Shown below is the MenuItemClick event handler. The case "&Start" works, but none of the other cases are even entered once the timer is running. A breakpoint on the "switch (sender.ToString()) line is never hit after Start.

        private void MenuItemClick (object sender, EventArgs e)
        {
            switch (sender.ToString ())
            {
                case "&Start":
                    generation = 0;

                    generationTimer.Interval = 1000;
                    generationTimer.Start ();

                    startToolStripMenuItem.Enabled = false;
                    stopToolStripMenuItem.Enabled  = true;
                    pauseToolStripMenuItem.Enabled = true;
                    break;
                case "Sto&p":
                    generationTimer.Stop ();
                    generationTimer.Dispose ();

                    startToolStripMenuItem.Enabled = true;
                    stopToolStripMenuItem.Enabled  = false;
                    break;
                case "&Pause":
                    generationTimer.Stop ();

                    pauseToolStripMenuItem.Enabled  = false;
                    resumeToolStripMenuItem.Enabled = true;
                    break;
                case "&Resume":
                    generationTimer.Start ();

                    resumeToolStripMenuItem.Enabled = false;
                    pauseToolStripMenuItem.Enabled  = true;
                    break;
            }
        }

Shown below is the Timer Tick event handler.

        private void GenerationTimer_Tick (object sender, EventArgs e)
        {
            generation++;

            grid = game.NewGeneration ();

            UpdateGrid ();
        }

What am I doing wrong? What must I do to have the UI respond to menu item clicks after Start?

Answer 1

    public bool [,] NewGeneration ()
    {
        // Set up a new working grid
        bool [,] newGrid = new bool [myColumns, myRows];

        // Scan the current grid.  For each cell in the current grid,
        // get a count of the live cells surrounding it
        for (int column = 0; column < myGrid.GetLength (0); column++)
        {
            for (int row = 0; row < myGrid.GetLength (1); row++)
            {
                int count = CheckStatus (column, row);

                // Based on the live cells surrounding the current cell
                // use the Rules of Life to determine whether the current
                // cell lives or dies
                if (myGrid [column, row])
                {
                    if (count == 2 || count == 3)
                        newGrid [column, row] = true;

                    if (count < 2 || count > 3)
                        newGrid [column, row] = false;
                }
                else
                {
                    if (count == 3)
                        newGrid [column, row] = true;
                }
            }
        }
        myGrid = newGrid;

        return newGrid;   // Update the main grid

    } // method NewGeneration

NewGeneration() uses a method called CheckStatus() shown below.

    private int CheckStatus (int column, int row)
    {
        int count = 0;

        // if upper-left is alive...
        if ((column - 1 >= 0 && row - 1 > 0) &&
            myGrid [column - 1, row - 1] == true)
            count++;

        // if upper is alive...
        if ((column - 1 >= 0) && myGrid [column - 1, row] == true)
            count++;

        // if upper-right is alive...
        if ((column - 1 >= 0 && row + 1 < myRows) &&
            myGrid [column - 1, row + 1] == true)
            count++;

        // if left is alive...
        if ((row - 1 >= 0) && myGrid [column, row - 1] == true)
            count++;

        // if right is alive...
        if ((row + 1 < myRows) && myGrid [column, row + 1] == true)
            count++;

        // if lower-left is alive...
        if ((column + 1 < myColumns && row - 1 >= 0) &&
            myGrid [column + 1, row - 1] == true)
            count++;

        // if lower is alive...
        if ((column + 1 < myColumns) && myGrid [column + 1, row] == true)
            count++;

        // if lower-right is alive...
        if ((column + 1 < myColumns &&
            row + 1 < myRows) &&
            myGrid [column + 1, row + 1] == true)
            count++;

        return count;

    } // method CheckStatus

Here is the code for UpdateGrid():

        private void UpdateGrid ()
        {
            var brushBlack = new SolidBrush (Color.Black);
            var brushWhite = new SolidBrush (SystemColors.Control);

            Graphics cellGraphics = panelGrid.CreateGraphics ();

            for (int i = 0; i < grid.GetUpperBound (0); i++)
                for (int j = 0; j < grid.GetUpperBound (1); j++)
                {
                    if (grid [i,j])
                        brush = brushBlack;
                    else
                        brush = brushWhite;

                    Rectangle rect = cells [i, j];

                    PanelGrid_Paint (this, new PaintEventArgs (cellGraphics, rect));
                }
            brushBlack.Dispose ();
            brushWhite.Dispose ();
        }

Answer 2

Here is the Paint event handler for updating the onscreen gride.

        private void PanelGrid_Paint (object sender, PaintEventArgs e)
        {
            // If the grid has already been drawn, then
            // we only need to handle filling the grid square
            // with black (create a life entity) or white (kill a life entity)
            if (gridDrawn)
            {
                blackPen = new Pen (Color.Black,1);

                e.Graphics.FillRectangle (brush,    e.ClipRectangle);

                // After filling the rectangle (especially with white),
                // we need to redraw the rectangle, some of whose sides
                // may have been overwritten by the brush.
                e.Graphics.DrawRectangle (blackPen, e.ClipRectangle);
                blackPen.Dispose ();
            }
            // If the grid has not yet been drawn (beginning of game)...
            else
            {
                //  Set up the grid, mark it as drawn,
                //  and set up the game to be played.
                SetupGrid (e);
                SetupGame ();
            }
        } // event handler PanelGrid_Paint

and here is the SetupGrid() method

        private void SetupGrid (PaintEventArgs e)
        {
            // Compute and save the number of columns and rows
            Columns = panelGrid.Width / cellWidth;
            Rows    = panelGrid.Height / cellWidth;

            // Instantiate a black pen to draw the grid
            blackPen = new Pen (Color.Black,1);

            // Create the array of Rectangle's to hold grid squares
            cells = new Rectangle [Columns, Rows];

            // Create and draw the grid squares
            for (int i = 0; i < Columns; i++)
            {
                for (int j = 0; j < Rows; j++)
                {
                    cells [i,j] = new Rectangle (i * cellWidth, 
                                                 j * cellWidth, 
                                                 cellWidth, 
                                                 cellWidth);

                    e.Graphics.DrawRectangle (blackPen, cells [i, j]);
                }
            }
            blackPen.Dispose ();

            gridDrawn = true;

        } // method SetupGrid

Answer 3

Hi NicholasPiazza-0093,
The System.Windows.Forms.Timer tick event executes on the UI thread. If the UI thread is busy doing something else, then the timer tick handler will have to wait.
So I suggest you try to use System.Timers.Timer which happened on threadpool threads.
Or try the BackgroundWorker which executes an operation on a separate thread.
Here is a related thread you can refer to.
Best Regards,
Daniel Zhang

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