WinForms PictureBox中的mouseClick事件有问题

Question

So, I'm currently trying to develop a small PaintBrush-like application as part of a college assigment, it's supposed to be made in a Windows Form and using C# as a language. So far I managed to code one of my teacher's algorithms to draw a line. It's supposed to work in the following manner, once I click the lineButton it should give me a prompt to click on two points in the PictureBox and once both have been selected I should click on the button again to plot the line, not very elegant or user friendly I know, but this is my first experience with UI design and handling events so I figured I'd keep it as simple as I can in order to give more focus to the pixel coloring algorithms themselves. It works as intended to draw one line (with a few minor glitches) but when I click it a second time it won't select two points in the PictureBox again. Here is my code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace CGExercicios
{
    public partial class MyPaint : Form
    {
        Bitmap drawArea;
        Color cor;
        private int drawX;
        private int drawY;
        private Point lineStart;
        private Point lineEnd;
        private bool mousePressed;
        private bool mouseInDrawArea;
        private bool pencilTool;
        private bool lineTool;
        private bool pointsSelected;
        private int numOfClicks; //numero de vezes que a imagem é clicada


        public MyPaint()
        {
            InitializeComponent();
            drawArea = new Bitmap(imagem.Size.Width, imagem.Size.Height);
            pencilTool = false;
            lineTool = false;
            cor = Color.Black; //cor padrao será a cor preta
            numOfClicks = 0;
            pointsSelected = false;
        }

        private void sobreToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }

        private void selectColor_Click(object sender, EventArgs e)
        {
            paletaCores.ShowDialog();            
            cor = paletaCores.Color;
        }

        private void imagem_MouseMove(object sender, MouseEventArgs e)
        {

            if (mouseInDrawArea) {

                posX.Text = "X: " + e.X;
                posY.Text = "Y: " + e.Y;

                /* Implementação da ferramenta do lápis */
                if (pencilTool)
                {
                    if (mousePressed)
                    {
                        drawX = e.X;
                        drawY = e.Y;

                        try
                        {
                            drawArea.SetPixel(drawX, drawY, cor);
                            imagem.Image = drawArea;
                        }
                        catch (System.ArgumentOutOfRangeException ecpt)
                        {}
                    }
                } 
            }

        }

        private void imagem_MouseDown(object sender, MouseEventArgs e)
        {
            mousePressed = true;
        }

        private void imagem_MouseUp(object sender, MouseEventArgs e)
        {
            mousePressed = false;
        }

        private void pencilButton_Click(object sender, EventArgs e)
        {
            if (!pencilTool)
                pencilTool = true;
            else
                pencilTool = false;
        }

        private void imagem_MouseLeave(object sender, EventArgs e)
        {
            mouseInDrawArea = false;
            posX.Text = "X:-";
            posY.Text = "Y:-";
        }

        private void imagem_MouseEnter(object sender, EventArgs e)
        {
            mouseInDrawArea = true;
        }

        private void lineButton_Click(object sender, EventArgs e)
        {
            /* Implementação do desenho das retas */
            if (!lineTool)
            {
                lineTool = true;
                numOfClicks = 0;
                if(lineTool) 
                    MessageBox.Show("Clique no ponto inicial e depois no ponto final e pressione o botao novamente");


            }

            else
            {
                if (pointsSelected)
                {
                    drawLine();                    
                }
                else 
                    MessageBox.Show("Pontos não selecionados");
            }



        }

        private void drawLine()
        {

            int dx = lineEnd.X - lineStart.Y;
            int dy = lineEnd.Y - lineStart.Y;
            int steps;
            double x, y; /* Armazenamento real */
            int ix, iy; /* Armazenamento inteiro para plotagem */
            double xincr, yincr;
            x = (double)lineStart.X;
            y = (double)lineStart.Y;

            drawArea.SetPixel(lineStart.X, lineStart.Y, cor);
            steps = Math.Max(Math.Abs(dx), Math.Abs(dy));

            xincr = (double)dx / steps;
            yincr = (double)dy / steps;

            for (int i = 0; i < steps; i++)
            {
                x += xincr;
                ix = (int)Math.Round(x);
                y += yincr;
                iy = (int)Math.Round(y);
                drawArea.SetPixel(ix, iy, cor);
            }
            imagem.Image = drawArea;

            resetLineDraw();

        }

        private void resetLineDraw()
        {

            DebugLabel.Text = "";
            pointsSelected = false;
            lineTool = false;
            numOfClicks = 0;
            imagem.MouseClick -= imagem_MouseClick;


        }

        private void imagem_MouseClick(object sender, MouseEventArgs e)
        {
            /* Captura os pontos inicias e finais se a ferramenta de desenho 
             * de retas esta habilitada */
            if (lineTool && !pointsSelected)
            {
                if (numOfClicks == 1) imagem.MouseClick -= imagem_MouseClick; 
                Point tmp = new Point(e.X, e.Y);

                if (numOfClicks == 0)
                {//Selecionou o primeiro ponto
                    lineStart = tmp;
                    DebugLabel.Text = "Primeiro ponto selecionado";
                }
                else
                {//Selecionou o segundo ponto
                    lineEnd = tmp;
                    pointsSelected=true;
                    DebugLabel.Text = "Segundo ponto selecionado";

                }
                numOfClicks++;
            }              
        }








    }
}

"imagem" is the PictureBox in question and the As you can see, I've tried resetting the variables utilized in it's mouseClick handler but the problem still persists. Is there a way to perhaps to "reset" the PictureBox so I can choose two points in it again? If not, then what am I doing wrong to cause the issue?

Answer 1

As far as i can see you are clearing the event imagem.MouseClick and never set it back again.

You have to reset the event when you click the button eg

imagem.MouseClick += imagem_MouseClick

Answer 2

For some reason you have decided to remove the MouseClick handler for the imagem picturebox. See below please,

private void resetLineDraw()
{
    DebugLabel.Text = "";
    pointsSelected = false;
    lineTool = false;
    numOfClicks = 0;

    // this removes the click handler from the picture box.
    // so, if you click on it anymore, nothing will happen.
    //-->  imagem.MouseClick -= imagem_MouseClick;
}

private void imagem_MouseClick(object sender, MouseEventArgs e)
{
    /* Captura os pontos inicias e finais se a ferramenta de desenho 
     * de retas esta habilitada */
    if (lineTool && !pointsSelected)
    {

        // same here
        // --> if (numOfClicks == 1) imagem.MouseClick -= imagem_MouseClick; 
        Point tmp = new Point(e.X, e.Y);

        if (numOfClicks == 0)
        {//Selecionou o primeiro ponto
            lineStart = tmp;
            DebugLabel.Text = "Primeiro ponto selecionado";
        }
        else
        {//Selecionou o segundo ponto
            lineEnd = tmp;
            pointsSelected=true;
            DebugLabel.Text = "Segundo ponto selecionado";

        }
        numOfClicks++;
    }              
}

remove those lines I commented and it should probably work.. at least that seems to be the most obvious problem.