using System;using System.Drawing;using System.Windows.Forms;using System.Reflection;using System.IO;using System.Threading;// Threading example created by Harsha T, May 2010.namespace ThreadingA{ //Delegate CallbackResult doesn't take any arguments and returns nothing. //Object of this delegate is used for triggering the function ResultReturn //once the thread completes its work. ResultReturn enables or disables the button //which are created by UI thread. So passing accessing these controls from //another thread is achieved through this.Invoke() function. And this.Invoke() takes a //delegate. public delegate void CallBackResult(); public partial class Form1 : Form { //Bitmap Image which holds the contents read from the stream. private Bitmap LenaImage; //object of type CallBackResult and is passed to this.Invoke() function. private CallBackResult cbResult; //Graphics object for pictureBox. private Graphics g; //This is our thread. Created and started when user clicks on the Start button. private Thread thread; public Form1() { InitializeComponent(); //Loads the content of stream to bitmap. LoadImage(); this.pictureBox.Image = this.LenaImage; //CallBackResult object is created. cbResult = new CallBackResult(ResultReturn); //Initially Stop and Pause buttons are dissabled. btnStop.Enabled = false; btnPause.Enabled = false; } //Following function, reads the Embedded Resource into Stream. private void LoadImage() { Assembly MyAssembly = Assembly.GetExecutingAssembly(); Stream LenaImageStream = MyAssembly.GetManifestResourceStream("ThreadingA.Resources.lena.JPG"); //Creates the LenaImage using the Stream. if (LenaImage == null) LenaImage = new Bitmap(LenaImageStream); //Close the stream which is no more required. LenaImageStream.Close(); } //Function is triggered using CallBackResult delegate. This function enables/disables //UI components which are created by UI thread. It is not allowed to access these //components from other threads. Winforms provides Invoke() function which takes //a delegate. So on any thread Invoke() function can be called. void ResultReturn() { this.btnStart.Enabled = true; this.btnStop.Enabled = false; this.btnPause.Enabled = false; } //This is triggered when user clicks on Start button. private void btnStart_Click(object sender, EventArgs e) { //Create a new thread. thread = new Thread(StartConversion); //Set buttons before thread start. btnStart.Enabled = false; btnStop.Enabled = true; this.btnPause.Enabled = true; //Start the thread by calling thread.Start(). thread.Start(); } //Thread is created to work on this function which Draw on the picture box. // The purpose of this application is to demonstrate threading, and therefore // we have deliberately chosen a slow way of image access - through // GetPixel(). private void StartConversion() { for (int i = 0; i < LenaImage.Height; i ) for (int j = 0; j < LenaImage.Width; j ) { //Get individual pixels. Color c = LenaImage.GetPixel(j, i); //This is standard formula for converting color image into grey scale //image. double r = 0.3 * c.R; double g = 0.59 * c.G; double b = 0.11 * c.B; if (r < 0) r = 0; if (g < 0) g = 0; if (b < 0) b = 0; int average = (int)Math.Ceiling((r g b)); Color greyValue = Color.FromArgb(average, average, average); UpdatePictureBox(j, i, greyValue); } //Calling Call back function when conversion completes this.Invoke(cbResult); } private void UpdatePictureBox(int x, int y, Color c) { //Graphics object is created using pictureBox Graphics object. using (g = pictureBox.CreateGraphics()) { Pen p = new Pen(c); //A small rectangle 1x1 is drawn at x,y with color c. g.DrawRectangle(p, x, y, 1, 1); p.Dispose(); } } //This is triggered when user clicks on stop button. private void btnStop_Click(object sender, EventArgs e) { threadKill(); //Setting button property. this.btnStart.Enabled = true; this.btnPause.Enabled = false; this.btnStop.Enabled = false; } private void btnPause_Click(object sender, EventArgs e) { //When you about to pause a thread, it is recommended to check the //thread state. If Thread state is not Suspended and is not SuspendRequested, //then suspend the thread. if (0 == (thread.ThreadState & (ThreadState.Suspended | ThreadState.SuspendRequested))) { thread.Suspend(); btnStop.Enabled = false; btnPause.Text = "Resume"; } else { btnPause.Text = "Pause"; thread.Resume(); btnStop.Enabled = true; } } private void Form1_FormClosed(object sender, FormClosedEventArgs e) { //Dispose the bitmap and graphics object. LenaImage.Dispose(); if (g != null) g.Dispose(); } private void btnClose_Click(object sender, EventArgs e) { threadKill(); this.Close(); } private void threadKill() { //When killing a thread, it is recommended to check the thread state. //Threads can be aborted when they are running. But when threads are suspended //or thread state is SuspendRequested, so in this case, thread.Resume is called //and threads are aborted. //Suspended threads cannot be aborted directly. CLR will not abort a suspected //thread. It will take thread to a state where GC can reclaim the memory. if(thread !=null) switch (thread.ThreadState) { case ThreadState.Suspended: case ThreadState.SuspendRequested: thread.Resume(); thread.Abort(); break; case ThreadState.Running: thread.Abort(); break; case ThreadState.Unstarted: break; } } }}
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