Refreshing a PictureBox in C#

I created a list of rectangles and draw them in a PictureBox. Elsewhere in the code we remove some rectangles from the list, but when I call PictureBox.Refresh() it shows the previous result: all the rectangles.

I tried creating a clone of the picture, and repainting all the rectangles one by one, but it has the same problem.

Please, can you give me some ideas on How to paint the current rectangles-list.

Rectangle r = lanes[i];//lanes is list of rectangles
Pen pen = new Pen(Color.Red, 2);
Grap开发者_如何学运维hics g = pictureBox1.CreateGraphics();
g.DrawRectangle(pen, r);

You haven't provided enough information, and I have no idea what "it does not give the correct one" means.

Your code above that draws the rectangles should go in the control's Paint event handler. And when you want the picture box to redraw, call the Invalidate method (you may also need to call the Update method).

Out of interest I went-ahead and implemented this, more or less as I think it should be done.

Here's 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.Windows.Forms;

namespace WindowsFormsApplication1
{
    public class Form1 : Form
    {
        private static List<Rectangle> rectangles = new List<Rectangle> {
            //            x,y,w,h
            new Rectangle(0,0,10,10),
            new Rectangle(10,10,10,10),
            new Rectangle(10,40,10,10),
            new Rectangle(60,20,10,10),
            new Rectangle(90,10,10,10),
        };
        private Label label1;

        private RectanglePictureBox rectPicBox1;

        public Form1() {
            InitializeComponent();
            this.rectPicBox1.Rectangles = rectangles;
        }

        private void rectPicBox1_Click(object sender, EventArgs e) {
            if ( rectangles.Count <= 0 ) {
                Console.Beep(); // nothing left to remove!
            } else {
                rectangles.RemoveAt(rectangles.Count - 1);
                rectPicBox1.Rectangles = rectangles;
            }
        }

        #region InitializeComponent (Modified Manually)

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent() {
            this.rectPicBox1 = new WindowsFormsApplication1.RectanglePictureBox();
            this.label1 = new System.Windows.Forms.Label();
            ((System.ComponentModel.ISupportInitialize)(this.rectPicBox1)).BeginInit();
            this.SuspendLayout();
            // 
            // rectPicBox1
            // 
            this.rectPicBox1.Anchor = ((System.Windows.Forms.AnchorStyles)((((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom)
                        | System.Windows.Forms.AnchorStyles.Left)
                        | System.Windows.Forms.AnchorStyles.Right)));
            this.rectPicBox1.BackColor = System.Drawing.SystemColors.ControlLightLight;
            this.rectPicBox1.Location = new System.Drawing.Point(1, 1);
            this.rectPicBox1.Name = "rectPicBox1";
            this.rectPicBox1.Size = new System.Drawing.Size(257, 131);
            this.rectPicBox1.TabIndex = 0;
            this.rectPicBox1.TabStop = false;
            this.rectPicBox1.Click += new System.EventHandler(this.rectPicBox1_Click);
            // 
            // label1
            // 
            this.label1.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Bottom | System.Windows.Forms.AnchorStyles.Left)
                        | System.Windows.Forms.AnchorStyles.Right)));
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(2, 138);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(254, 13);
            this.label1.TabIndex = 1;
            this.label1.Text = "Clicking on the picture to removes the last rectangle.";
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(259, 156);
            this.Controls.Add(this.label1);
            this.Controls.Add(this.rectPicBox1);
            this.Name = "Form1";
            this.Text = "Rectangles";
            ((System.ComponentModel.ISupportInitialize)(this.rectPicBox1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        #region Component Model

        private System.ComponentModel.IContainer components = null;

        protected override void Dispose(bool disposing) {
            if ( disposing && (components != null) ) {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #endregion


    }

    ////////////////////////////////////////////////////////////////////////////

    class RectanglePictureBox : PictureBox
    {
        public static Color[] _colors = { 
            Color.Red, Color.Green, Color.Blue, Color.Orange 
        };

        public List<Rectangle> Rectangles {
            set { Image = ImageOf(value); }
        }

        private Bitmap ImageOf(List<Rectangle> rectangles) {
            Bitmap result = new Bitmap(Size.Height, Size.Width);
            Graphics graphics = Graphics.FromImage(result);
            for ( int i = 0; i < rectangles.Count; ++i ) {
                Brush brush = new SolidBrush(_colors[i % _colors.Length]);
                graphics.FillRectangle(brush, rectangles[i]);
            }
            return result;
        }

    }


}

This code is published with NO warranties (explicit or implied). It's all yours. Do whatever you like with it. Just whatever happens, IT'S NOT MY PROBLEM!

Cheers. Keith.