Question

I have code which will draw a graph that scales if the user attempts to resize the form(by dragging the form’s corners). The form will get an x and y co-ordinate in a textbox. When a button is pushed, i want to plot the point which they have indicated. However, the Click event contains the parameters Object Sender and EventArgs e. The OnPaint method (which i am overriding in order to draw the graph) has the parameter PaintEventArgs.

Due to this, when the button is clicked i cannot do the following code:

g.DrawString("♫", new Font("Calibri", 12), new SolidBrush(Color.HotPink), (PlotArea.X + (7 - xMin)* PlotArea.Width/(xMax - xMin)), (PlotArea.Bottom - (6 - yMin) * PlotArea.Height / (yMax - yMin)));

This is because “g” is of type PaintEventArgs. How do i get around this so that in the onClick method i can plot the co-ordinate?

My code is as follows:

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

namespace PlotIt
{
    public partial class Form1 : Form
    {
        public static List<TheList> GraphPoints = new List<TheList>();

        //Define the drawing area
        private Rectangle PlotArea;
        //Unit defined in world coordinate system:
        private float xMin = 0f;
        private float xMax = 10f;
        private float yMin = 0f;
        private float yMax = 10f;
        //Define the offset in pixel:
        private int offset = 150;
        Graphics g;

        Boolean buttonPressed = false; 
        public Form1()
        {
            InitializeComponent();
            this.SetStyle(ControlStyles.ResizeRedraw, true);
            this.BackColor = Color.White;

        }

        protected override void OnPaint(PaintEventArgs e)
        {
            g = e.Graphics;

            //Calculate the location and size of the drawing area
            //within which we want to draw the graphics:
            Rectangle rect = ClientRectangle;

            PlotArea = new Rectangle(rect.Location, rect.Size);
            PlotArea.Inflate(-offset, -offset);

            g.DrawRectangle(Pens.Black, PlotArea);

            Pen aPen = new Pen(Color.Green, 3);
            g.DrawLine(aPen, Point2D(new PointF(5, 0)), Point2D(new PointF(5, 10)));
            g.DrawLine(aPen, Point2D(new PointF(0, 5)), Point2D(new PointF(10, 5)));

            aPen.Dispose();
            g.Dispose();


        }



        private PointF Point2D(PointF ptf)
        {
            PointF aPoint = new PointF();

            aPoint.X = PlotArea.X + (ptf.X - xMin) * PlotArea.Width / (xMax - xMin);

            aPoint.Y = PlotArea.Bottom - (ptf.Y - yMin) * PlotArea.Height / (yMax - yMin);

            return aPoint;
        }



        private void btnPlotGraph_Click(object sender, EventArgs e)
        {



            g.DrawString("♫", new Font("Calibri", 12), new SolidBrush(Color.HotPink),    (PlotArea.X + (7 - xMin)* PlotArea.Width/(xMax - xMin)), (PlotArea.Bottom - (6 - yMin) * PlotArea.Height / (yMax - yMin)));
        }



    }

}

Answer 1

Look into the Control.CreateGraphics Method. That should allow you to get the Graphic object you need.

Graphics g = this.CreateGraphics();
g.DrawString("♫", new Font("Calibri", 12), new SolidBrush(Color.HotPink), (PlotArea.X + (7 - xMin)* PlotArea.Width/(xMax - xMin)), (PlotArea.Bottom - (6 - yMin) * PlotArea.Height / (yMax - yMin)));
g.Dispose();