Develop Reference

Update progress for C# WPF application time-taking task

The question is pretty trivial: I need to update progress on WPF application while time-consuming calculation is processed. In my tries, I've made some googling and finally based on the first code snippet from this solution: How to update UI from another thread running in another class. And here's my code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Threading;
namespace ThreadTest
{
public class WorkerClass
{
public int currentIteration;
public int maxIterations = 100;
public event EventHandler ProgressUpdate;
public void Process()
{
this.currentIteration = 0;
while (currentIteration < maxIterations)
{
if (ProgressUpdate != null)
ProgressUpdate(this, new EventArgs());
currentIteration++;
Thread.Sleep(100); // some time-consuming activity takes place here
}
}
}
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void btnStart_Click(object sender, RoutedEventArgs e)
{
WorkerClass wItem = new WorkerClass();
wItem.ProgressUpdate += (s, eArg) => {
Dispatcher.BeginInvoke((Action)delegate() { txtProgress.Text = wItem.currentIteration.ToString(); });
};
Thread thr = new Thread(new ThreadStart(wItem.Process));
thr.Start();
// MessageBox.Show("Job started...");
while (thr.IsAlive == true)
{
Thread.Sleep(50);
}
MessageBox.Show("Job is done!");
}
}
}
The issue is that if I use Dispatcher.Invoke, than the working thread (thr) gets into WaitSleepJoin state after the first cycle pass and does not resume, therefore the entire application freezes. I've googled several suggestions to use Dispatcher.BeginInvoke instead, but in this case the progress is not updated untill the process finishes the work. I guess the issue is related to switching between threads, but cannot get exact point.

This is a classic "Invoke deadlock" scenario. Stack Overflow has a number of existing questions addressing this problem for Winforms, but I could only find one related question in the WPF context (Deadlock when thread uses dispatcher and the main thread is waiting for thread to finish), but that one isn't precisely the same question, or at least doesn't have answers (yet) that would directly address your question, and the question and answers themselves are poorly enough formed that I feel your question warrants a fresh answer. So…
The basic issue is that you have blocked your UI thread waiting on the process to finish. You should never do this. You should never block the UI thread for any reason. It should be obvious that if you wait for any reason in code running in the UI thread, then the UI itself cannot respond to user input or do any sort of screen refresh.
There are lots of possible ways to address this, but the current idiom for dealing with this would be to use async and await, along with Task to run your process. For example:
private async void btnStart_Click(object sender, RoutedEventArgs e)
{
WorkerClass wItem = new WorkerClass();
wItem.ProgressUpdate += (s, eArg) => {
Dispatcher.BeginInvoke((Action)delegate() { txtProgress.Text = wItem.currentIteration.ToString(); });
};
Task task = Task.Run(wItem.Process);
// MessageBox.Show("Job started...");
await task;
MessageBox.Show("Job is done!");
}
Note that while the above declares the async method as void, this is the exception to the rule. That is, normally one should always declare async methods as returning Task or Task<T>. The exception is situations such as this, where the method is an event handler and so is required to match an existing signature where the method must be declared to return void.

I ran your code as it is, and commented out this :
while (thr.IsAlive == true)
{
Thread.Sleep(50);
}
Everything worked as expected.
/Edit after user comment/
To get notified of processing completion, do these changes :
a. public event EventHandler ProgressCompleted; in your WorkerClass.
b.
if (ProgressCompleted != null)
ProgressCompleted(this, new EventArgs());
after your while finishes in Process() method.
c. In your BtnStart_Click before creating thread.
wItem.ProgressCompleted += (s1, eArgs1) =>
{
MessageBox.Show("Job is done!");
};

Cross Thread Operation - Invoked function calls another function C#

I have a program which uses many threads, when one of the threads found an answer (I think the context doesn't really matter) - it announces it, and then the first thread I created calles a function in a user control class using Invoke.
I checked - and if I change any attributes in this function, I do not get the cross-thread operation. But this function starts a timer (System.Timers.Timer) -> so the function of the "Elapsed" event is called. Inside it I am trying to change an attribute, and that causes cross-thread operation. What am I doing wrong? Isn't it possible to have the invoked function calling another function and then change the attributes in there?
By the way, is it wrong to invoke functions using the delegate? I mean, having the delegate as an attribute of the class I need it in, and then using delegAttributeName.Invoke(parameters) - and not this.Invoke(new Delegate(), parameters);
Heres part of the code:
Thats is where I invoke the function:
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;
using System.Threading;
namespace Nim_Assignment_3
{
public delegate void drawDeleg(Color c, int amount, int rowNumber);
public partial class Nim : Form
{
private event drawDeleg myDrawDeleg;
private void CheckXor()
{
if (this.foundToPaint)
{
this.myDrawDeleg.Invoke(this.currentTurnColor, this.amountToPaint, this.rowToPaint);
this.drawWait.WaitOne();
this.foundToPaint = false;
if (this.currentTurnColor == Color.Blue)
this.currentTurnColor = Color.Red;
else
this.currentTurnColor = Color.Blue;
}
}
// the invoked function:
private void callFillPencils(Color c, int amount, int rowNumber)
{
this.rows[rowNumber].fillPencils(c, amount);
}
}
}
And this is the function that the invoked function is calling - and the one it calls (the timer-elapsed event function):
(fillPencils - the function that the invoked function in the Form class (Nim) is calling):
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Timers;
namespace Nim_Assignment_3
{
public partial class PencilsUC : UserControl
{
private PictureBox[] pencils;
public static Image grayPencil = new Bitmap("GrayPen.bmp"), bluePencil = new Bitmap("BluePen.bmp"), redPencil = new Bitmap("RedPen.bmp");
private int amountOfPencils, amountOfPencilsLeft, currIndex, currAmount;
private System.Timers.Timer timer;
private Color currColor;
public event FinishedDrawing drawFinishedDeleg;
public PencilsUC()
{
// intializing things in the constructor...
this.timer = new System.Timers.Timer();
this.timer.Interval = 100;
this.timer.Elapsed += new ElapsedEventHandler(timer_Tick);
}
public void timer_Tick(object sender, EventArgs e)
{
// THE THING THAT MAKES THE CROSS THREAD-OPERATION: THE LINE INSIDE THE "if"
if (this.currColor == Color.Blue)
pencils[currIndex--].Image = bluePencil;
else
pencils[currIndex--].Image = redPencil;
this.currAmount--;
if (this.currAmount == 0)
{
this.timer.Stop();
if (this.drawFinishedDeleg != null)
this.drawFinishedDeleg.Invoke(this, new EventArgs());
}
}
public void fillPencils(Color c, int amount)
{
MessageBox.Show("Hello");
this.currColor = c;
this.currAmount = amount;
this.timer.Start();
}
}
}
(THE CROSS THREAD OPERATION HAPPENS INSIDE THE TIMER_TICK FUNCTION)
I used the windows forms timer at first but for some reason it didn't get to the tick-event function (timer.Start() was called but I put a message box in the tick function and it didnt get in there so I changed it - I saw some answers that said it was better)
I would love some help, I am sorry for the long post, I just wanted to be as clear as I can...
Thanks a lot in advance! :)

Use a Windows.Forms.Timer instead of a System.Timers.Timer. (You'll need to change the names of a few properties/events, i.e. Tick instead of Elapsed, but it's straightforward enough.)
The Timer in the Form's namespace marshals the Tick event into the UI thread, unlike the systems timer which executes the event in a thread pool thread.
If you really prefer to use the system's timer, then you can set the SynchronizingObject to have it marshall it's event to the UI thread:
timer.SynchronizingObject = this;
Note that the UserControl is a synchronizable object.

You need to .Invoke onto the main thread to change any controls.
Image image;
if (this.currColor == Color.Blue)
image = bluePencil;
else
image = redPencil;
this.Invoke(new MethodInvoker(() => pencils[currIndex--].Image = image));
The => is the syntax for a lambda (called anonymous method in other languages). Think about it as a one-line function.
() => pencils[currIndex--].Image = image
is the same as:
void SetImage(Image image, ref int currIndex) {
pencils[currIndex--].Image = image;
}
MethodInvoker provides a simple delegate that is used to invoke a method with a void parameter list

The easiest fix as you already made code would be to set SynchronizingObject of the Timer to Form, so timer would run on UI thread.

How do I access variables from a different thread?

Getting error: Cross-thread operation not valid: Control 'label1' accessed from a thread other than the thread it was created on.
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.Threading;
using System.Windows.Forms;
namespace WindowsFormsApplication2
{
public partial class Form1 : Form
{
string CONNECTING = "Connecting to server...";
string GETTING_DATA = "Getting data...";
string CONNECT_FAIL = "Failed to connect!";
string CONNECT_SUCCESS = "Connection established!";
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Thread t1 = new Thread(run);
t1.Start();
}
public void run() {
label1.Text = CONNECTING;
}
}
}
How do I properly fix this? I've tried using CheckForIllegalCrossThreadCalls = false; but that obviously causes errors.
I'd also like to know how I can stop the thread, since it can't be accessed anymore outside of that function.
Thanks in advance!

Try using BeginInvoke:
public void run()
{
label1.BeginInvoke(new Action(() =>
{
label1.Text = CONNECTING;
}));
}
Only the UI thread can update UI elements in a Windows Forms app. Other threads need to use BeginInvoke to update the UI.
ORGINAL: i assumed this was a WPF app and said to use this.Dispatcher, but Dispatcher isn't in Windows Forms apps.

Accessing a control from different threads
In WinForms App you can ony access directly a Control from the thread it was created.
To do such a task you will need to use InvokeRequired property of a control to see if you must use Invoke inorder to force a call of the action from the original thread.
A public method that might be accessed from any thread including the original would look like this:
public void run() {
if (label1.InvokeRequired) //Is this method being called from a different thread
this.Invoke(new MethodInvoker(()=> label1.Text = CONNECTING));
else //it's cool, this is the original thread, procceed
label1.Text = CONNECTING;
}
But if you are absolutly sure that run() method will be called only from the thread, consider not even checking if InvokeRequired and immediatly call Invoke
Further information: http://msdn.microsoft.com/en-us/library/ms171728(v=vs.80).aspx
Stopping a thread in progress
Simples is to use t1.Abort(); method of a Thread. This will throw and exception forcing it to stop where ever it was. this is great for threads that do not do any long processing so stopping it won't cause any problems.
If you do do proccesing in your thread, which means you can't just stop it in the middle then I suggest you to use a boolean that will indicate that the thread must cancel ASAP.
private bool isCancelRequired = false;
public void run() {
while(true) {
//do long processing..
if (isCancelRequired)
break;
}
}
More advanced methods: http://www.yoda.arachsys.com/csharp/threads/shutdown.shtml

Update of Windows Form - C#

Explanation:
Structure: Windows form - three components: Text box, Text box Response and button.
Problem: I am moving motor with C# windows form: I am starting the motor and reversing
the direction of movement of motor with single button click with 10 second delay in the middle. i.e. I start the motor, have 10 sec delay and then reverse the motor. I want to display "Start" at the beginning and "End" at the end of the 10 second delay. I have tried using thread but it does not work. But I am only able to see "Finish" not "Start" in text box. The code is below:
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;
using System.Threading;
namespace SampleThreadProgram
{
public partial class Form1 : Form
{
static EventWaitHandle _waitHandle = new AutoResetEvent(false);
delegate void SetTextCallback(string text);
void SetText(string text)
{
if (textBox.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(SetText);
BeginInvoke(d, new object[] { text });
}
else
{
textBox.Text = text;
}
}
void UpdateTextBox(string message)
{
SetText(message);
_waitHandle.Set();
}
void Wait()
{
for (ulong i = 0; i < 10000; i++)
{
for (ulong j = 0; j < 100000; j++)
{
}
}
}
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
UpdateTextBox("Start");
_waitHandle.WaitOne();
Thread.Sleep(10000);
UpdateTextBox("Finish");
}
}
}

You should not use a big long for loop to make the computer wait for a while. Use Thread.Sleep at the very least.
You should use a BackgroundWorker to do what you're trying to do. Set the start text in the button click event, then start the background worker. You can have the DoWork event do some work (in this case sleeping) and use the WorkerCompleted event to update the UI.
The nice thing about using the background worker is that you don't need to worry about updating code form non-UI threads. In the button click event you can update the text of the textbox directly, and the BackGroundWorker thread will already ensure that the Completed event runs in the UI thread, so even there you can directly access UI controls. The BGW is specifically designed to make this exact case easier.

There's not enough time for the UI to update. Add an Application.DoEvents(); after the SetText(message); in UpdateTextBox.

moving an image on another image

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 d3
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
pictureBox1.Image = Image.FromFile("C:\\Users\\ocean\\Desktop\\deneme.png");
pictureBox1.Location = new Point(0, 0);
pictureBox2.Image = Image.FromFile("C:\\Users\\ocean\\Desktop\\pul1.png");
}
protected override void OnMouseClick(MouseEventArgs e)
{
Graphics theGraphics = Graphics.FromHwnd(this.Handle);
for (int i = 0; i < 200; i += 5)
{
pictureBox2.Location = new Point(i, 100);
theGraphics.Flush();
System.Threading.Thread.Sleep(50);
pictureBox2.Invalidate();
}
}
}
}
In this code picturebox2 is moving ok but previous locations image stay ON THEuntil the loop finishes. When loop finished the older parts would be erased. I dont want the previous paintings inside the loop I just want to move on pictureBox1. Im new at C# so please help me:) In J2Me I was using flushgraphics but here I tried and it did not work and If you can give an example I would be happy .

In C#, just as in Swing, if you are on the UI or event thread, nothing that you change will be noticed by the user until you are done.
So, if you want to move these, your best bet is to start by getting off the UI thread, by starting a new thread, and then go through your loop.
But, the problem is that you will need to be on the UI thread to make the changes.
This is why your sleep didn't work, you are just putting the event thread to sleep, btw.
Which version of C# are you using? There are many options on creating a thread, and on working with the UI thread.
Here is a link to creating a thread:
http://msdn.microsoft.com/en-us/library/7a2f3ay4(v=vs.80).aspx
Here is a way to deal with how to get back to the UI thread:
http://blogs.msdn.com/b/csharpfaq/archive/2004/03/17/91685.aspx.
For example, to create a thread you can do this, which came from http://www.rvenables.com/2009/01/threading-tips-and-tricks/
I do my threads this way as I find it simpler to see what is happening.
(new Thread(() => {
DoLongRunningWork();
MessageBox.Show("Long Running Work Finished!");
}) { Name = "Long Running Work Thread",
Priority = ThreadPriority.BelowNormal }).Start();
The most complete answer on how to do your update on the UI thread would be this question:
How to update the GUI from another thread in C#?
UPDATE:
For the part where it states to do long running work, you can add this before the thread block:
TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
Then you can do this inside your thread:
(new Task(() =>
{
//copy pixel
pictureBox2.Invalidate(); // You may want to just invalidate a small block around the pixel being changed, or every some number of changes.
}))
.Start(uiScheduler);
By making these changes you could simplify making the change you want, but some of this may be more complex than what you want, which is why I gave some other links to give more information. But, for more on using Task you can look at this excellent blog:
http://reedcopsey.com/2010/03/18/parallelism-in-net-part-15-making-tasks-run-the-taskscheduler/