click button event problem

Question

I want to do a simple thing: create windows form with a button and get line drawn when I click button. So far no luck with button click event, e.g. how do I make that line be drawn via private void button1_Click(object sender, EventArgs e)?

Is there a more appropriate beginners forum or I can post here?

thanks

Jonas

namespace Example1_1

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

            this.SetStyle(ControlStyles.ResizeRedraw, true);

            this.BackColor = Color.White;

        }

        public void OnPaint(object sender, PaintEventArgs e)

        {

            Graphics g = e.Graphics;

            g.PageUnit = GraphicsUnit.Inch;

            Pen blackPen = new Pen(Color.Black, 5 / g.DpiX);

            g.DrawLine(blackPen, 0, 0, 1, 1);

        }

        private void button1_Click(object sender, EventArgs e)

        {

            Application.Run(new Onpaint());

        }

    }

}

Jonas Baltrusaitis · Answer

Mike I went on to create a bit more complicated example. It works but for some reason in the middle of debuggin it throws out this Parameter is not valid exception and I just have no idea why. could you take a look at it? The problem is in Program.cs for some reason with the problematic line being Application.Run(new Form1()); Below is Form1.cs 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 Example1_2 { public partial class Form1 : Form { //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 = 30; private bool m_bPressed; public Form1() { InitializeComponent(); this.SetStyle(ControlStyles.ResizeRedraw true); this.BackColor = Color.White; } protected override void OnPaint(PaintEventArgs e) { Graphics 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); //Draw ClientRectangle and PlotArea using Pen: g.DrawRectangle(Pens.Red rect); g.DrawRectangle(Pens.Black PlotArea); if (m_bPressed) { //draw a line from point (32) to point (67) //using a pen with a width of 3 pixels: Pen aPen = new Pen(Color.Green 3); g.DrawLine(aPen Point2D(new PointF(3 2)) Point2D(new PointF(6 7))); 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 Form1_Load(object sender EventArgs e) { } private void toolStripButton1_Click(object sender EventArgs e) { m_bPressed = true; Invalidate(); } } }

Mike Gold · Answer

Hi Jonas glad it worked for you finally. Your solution is correct. -Mike

Jonas Baltrusaitis · Answer

so I bastardized your code a bit and got mine working 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 Example1_1 { public partial class Form1 : Form { private bool m_bPressed; public Form1() { InitializeComponent(); this.SetStyle(ControlStyles.ResizeRedraw true); this.BackColor = Color.White; } private void Form1_Load(object sender EventArgs e) { } protected override void OnPaint(PaintEventArgs e) { if (m_bPressed) { Graphics g = e.Graphics; g.PageUnit = GraphicsUnit.Inch; Pen blackPen = new Pen(Color.Black 4 / g.DpiX); g.DrawLine(blackPen 0 0 1 1); } } private void button1_Click(object sender EventArgs e) { m_bPressed = true; Invalidate(); } } }

Jonas Baltrusaitis · Answer

I am afraid not working for me. First and foremost there is no button generated should I create button myself? Then I deleted everything from public partial class Form1 : Form down and paste your code I am getting compilation error Error 1 'Example1_13.Form1' does not contain a definition for 'Form1_Load' and no extension method 'Form1_Load' accepting a first argument of type 'Example1_13.Form1' could be found (are you missing a using directive or an assembly reference?) c:\documents and settings\jonas\my documents\visual studio 2010\Projects\Example1_13\Example1_13\Form1.Designer.cs 40 55 Example1_13 this paqrticularly I don;t understand as my Form1 : Form didn;t change names why wouldn;t it find it all of a sudden?..

Mike Gold · Answer

Hi Jonas I omitted nothing obvious this code was pasted from an app I made specifically to illustrate how to do this. I ran the code before I sent it to you so I know it works. It draws a red line from the upper left hand corner of the screen to the bottom after you press the button. I did not however paste the whole project but I'll list the steps to recreate it. 1. Go to New Projects and choose window forms application 2. REplace the Form class generated with the class I sent you above. 3. compile and run 4. press the button 5. see the diagnol red line appear from upper left to bottom right corner of the form

Jonas Baltrusaitis · Answer

thanks. you clearly omitted something probably very obvious because the code above in VS2010 gives a window but no line pops up when I click the buttin

Mike Gold · Answer

You do not ever want to call the OnPaint event directly like you did. What you need to do is handle all your drawing in the paint event handler but set a flag to indicate that you want the drawing to take place. When do you set the flag? set the flag in the button event handler then invalidate the form to force the paint event handler to fire namespace LineOnButtonPress { public partial class Form1 : Form { private bool m_bPressed; public Form1() { InitializeComponent(); } private void Form1_Paint( object sender PaintEventArgs e) { if (m_bPressed) { e.Graphics.DrawLine( Pens .Red 00 ClientRectangle.Width ClientRectangle.Height); } } private void button1_Click( object sender EventArgs e) { m_bPressed = true ; Invalidate(); } } }