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How to run a windows form from a backgroundworker runnig through another backgroundworker?

this is the simplified plan for a solution:
for some reasons i need to run a windows form through a backgroundworker that is runnig by another backgroundworker, when the new windows form loads, the older backgroundworker must pause. i write the code like this :
creating a class with name : temp
public class temp
{
static public BackgroundWorker backgroundWorker1 = new BackgroundWorker() { WorkerSupportsCancellation = true };
static public EventWaitHandle ew = new EventWaitHandle(false, EventResetMode.ManualReset);
static public BackgroundWorker back = new BackgroundWorker() { WorkerSupportsCancellation = true };
}
the codes for form1 are :
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Control.CheckForIllegalCrossThreadCalls = false;
temp.backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
temp.back.DoWork += new DoWorkEventHandler(back_DoWork);
}
void back_DoWork(object sender, DoWorkEventArgs e)
{
Form2 f = new Form2();
f.Show();
}
private void button1_Click(object sender, EventArgs e)
{
temp.backgroundWorker1.RunWorkerAsync();
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
temp.back.RunWorkerAsync();
if (temp.backgroundWorker1.CancellationPending)
temp.ew.WaitOne();
}
}
}
and the codes of form2 goes here :
namespace WindowsFormsApplication1
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
}
private void Form2_Load(object sender, EventArgs e)
{
temp.backgroundWorker1.CancelAsync();
temp.ew.Reset();
}
}
}
by clicking the button1 from form1 the temp.backgroundworker1 runs and then in the DoWork of temp.backgroundworker1, the temp.back runs and then FORM2 LOADS BUT THE FORM2 HANGS AND BECOMES USELESS AND YOU CANNOT USE THAT ANY MORE.
where did i wrong ?
the whole plan that i'm going to execute is :
we have a For loop that processes every row of a DataGridView.
each time in a certain point, another windowsform opens
and it stops the loop until the user inserts the information and then click on OK button, the windowsform closes and the loop keep on working. i dont know what to do.......
even if i dont cancel working of the temp.backgroundworker in form2load like the code below, the Form2 is useless
private void Form2_Load(object sender, EventArgs e)
{
}

Do not use any UI operation in the work thread (DoWork method). Maybe that's why you set the CheckForIllegalCrossThreadCalls property, but your app will not work properly just suppresses the error when the debugger is attached.
See my answer here for the correct usage of the BackgroundWorker (that is about canceling but you can see the operations in UI and worker thread).
In this particular case what you can use a similar volatile bool to sign the UI thread that the form can be shown. Or, if you want to send different messages between the threads, use a ConcurrentQueue<T> to write and read messages:
public partial class Form1 : Form
{
private enum Message
{
ShowForm2,
SuspendWork,
ResumeWork,
FinishWorker1
// ... and whatever you want
}
private Timer timer;
private ConcurrentQueue<Message> messagesToUI = new ConcurrentQueue<Message>();
private ConcurrentQueue<Message> messagesToWorker = new ConcurrentQueue<Message>();
public Form1()
{
InitializeComponent();
timer = new Timer(this);
timer.Interval = 10;
timer.Tick += PollUIMessages;
timer.Enabled = true;
}
void PollUIMessages(object sender, EventArgs e)
{
// do we have a new message?
Message message;
if (messagesToUI.TryDequeue(out message))
{
switch (message)
{
case Message.ShowForm2:
Form2 f = new Form2();
f.Show();
// todo: in Form2.Close add a Resume message to the messagesToWorker
break;
// ... process other messages
}
}
}
void back_DoWork(object sender, DoWorkEventArgs e)
{
// Here you are in the worker thread. You can send a message to the
// UI thread like this:
messagesToUI.Enqueue(Message.ShowForm2);
bool isWorking = true;
// and here you can poll the messages to the worker thread
while (true)
{
Message message;
if (!messagesToWorker.TryDequeue(out message))
{
// no message: idle or work
if (isWorking)
DoSomeWork(); // do whatever you want
else
Thread.CurrentThread.Sleep(10);
continue;
}
switch (message)
{
case Message.FinishWorker1:
// finishing the worker: jumping out
return;
case Message.SuspendWork:
isWorking = false;
break;
case Message.ResumeWork:
isWorking = true;
break;
}
}
}

NullReferenceException happens when sending message back to message dialog from BackGroundWorker

It's a C# winform .Net framework 2.0 project: The time-consuming network transferring jobs run in a BackupgroundWorker. In this backgroundwork thread, SynchronizationContext method is used to send the current job title to a message dialog in the main UI thread. However, in my code, thread racing problem happens and "NullReferenceException" is given sometime (not always, but randomly). Here is my code:
private void DoBtn_Click(object sender, EventArgs e)
{
m_msgForm = new MsgForm(); //m_msgForm is a member variable of the class, and MsgForm is a form class with a "public static SynchronizationContext synContext"
m_msgForm.UpdateMsg("starting ..."); //UpdateMsg is public method to show progress information
BackgroundWorker myBackgroundWorker = new BackgroundWorker();
myBackgroundWorker.DoWork +=new DoWorkEventHandler(myBackgroundWorker_DoWork);
myBackgroundWorker.RunWorkerCompleted +=new RunWorkerCompletedEventHandler(myBackgroundWorker_RunWorkerCompleted);
myBackgroundWorker.RunWorkerAsync(theBackgroundArgument);
m_msgForm.ShowDialog(); //show as a modal dialog
}
And in the Background worker thread:
private void myBackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
//... some code
string msgText ="doing job: " +job.Title;
RestoreMsgForm.synContext.Send(m_msgForm.UpdateMsg, msgText); //send message to m_msgForm in the UI thread
//... some code
}
The problem is : sometime the "RestoreMsgForm.synContext.Send() in the backgroundworker thread will run before m_msgForm.ShowDialog() in the UI thead.
And in this case, NullReferenceException will be throw.
How to solve this problem? thanks.
the definition of RestoreMsgForm is
public partial class RestoreMsgForm : Form
{
public static SynchronizationContext synContext;
public RestoreMsgForm()
{
InitializeComponent();
}
private void RestoreMsgForm_Load(object sender, EventArgs e)
{
synContext = SynchronizationContext.Current;
}
public void UpdateMsg(object msg)
{
msgLabel.Text = (string)msg;
}
}

See if it works like this instead:
private void DoBtn_Click(object sender, EventArgs e)
{
m_msgForm = new MsgForm(); //m_msgForm is a member variable of the class, and MsgForm is a form class with a "public static SynchronizationContext synContext"
m_msgForm.UpdateMsg("starting ..."); //UpdateMsg is public method to show progress information
BackgroundWorker myBackgroundWorker = new BackgroundWorker();
myBackgroundWorker.DoWork += new DoWorkEventHandler(myBackgroundWorker_DoWork);
myBackgroundWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(myBackgroundWorker_RunWorkerCompleted);
myBackgroundWorker.WorkerReportsProgress = true;
myBackgroundWorker.ProgressChanged += new ProgressChangedEventHandler(myBackgroundWorker_ProgressChanged);
myBackgroundWorker.RunWorkerAsync(theBackgroundArgument);
}
private void myBackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = (BackgroundWorker)sender;
worker.ReportProgress(-1);
//... some code
string msgText = "doing job: " + job.Title;
worker.ReportProgress(0, msgText);
//... some code
worker.ReportProgress(0, "...other text...");
//... some code
worker.ReportProgress(0, "...etc...");
}
void myBackgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
if (e.ProgressPercentage == -1)
{
m_msgForm.ShowDialog(); //show as a modal dialog
}
else
{
m_msgForm.UpdateMsg(e.UserState.ToString);
}
}
*Note that we have to set .WorkerReportsProgress = true for the BackgroundWorker() so we can use ReportProgress() and receive the ProgressChanged() event.

Thread is not working

Can someone tell me why the below code is not working?
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Thread t = new Thread(rtb2);
t.Start();
}
private void rtb2()
{
try
{
richTextBox1.Text = "1";
}
catch(InvalidOperationException ex)
{
MessageBox.Show("HI");
}
}
}

The problem is your attempting to modify a Winforms UI element from a background thread. This is specifically not allowed by the WinForms model. UI elements can only be modified from the main thread. You need to use Control.Invoke in order to get the context back onto the appropriate thread.
private void rtb2() {
Action action = delegate {
richTextBox1.Text = "1";
};
try {
this.Invoke(action);
} catch(InvalidOperationException ex) {
MessageBox.Show("HI");
}
}

updating gui from another class c#

hey i am new to c# plz help.
i am writing a program that sorts data in a file and it is a time consuming process so i thought that i should run it in a separate thread and since it has alot of step so i made a new class for it. the problem is that i want to show the progress in the main GUI and i know for that i have to use Invoke function but the problem is that the form control variables are not accessible it this class. what should i do ??????
sample code:
public class Sorter
{
private string _path;
public Sorter(string path)
{
_path = path;
}
public void StartSort()
{
try
{
processFiles(_path, "h4x0r"); // Just kidding
}
catch (Exception e)
{
MessageBox.Show("Error: " + e.ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
private void processFiles(string Dir, string[] key)
{
/* sorting program */
}
and it is used as
public partial class Form1 : Form
{
Sorter sort;
public Form1()
{
InitializeComponent();
}
private void browseBtn_Click(object sender, EventArgs e)
{
if (folderBrowserDialog1.ShowDialog() == DialogResult.OK)
textBox1.Text = folderBrowserDialog1.SelectedPath;
}
private void startBtn_Click(object sender, EventArgs e)
{
if (startBtn.Text == "Start Sorting")
{
Thread worker = new Thread(new ThreadStart(delegate() {
sort = new Sorter(textBox1.Text);
sort.StartSort(); }));
worker.start();
}
else
MessageBox.Show("Cancel");//TODO: add cancelling code here
}
}
plz help..

Add an Event to your class that is doing the multi-threaded work, that triggers when the progress changes. Have your form subscribe to this event and update the progress bar.
Note ProgressEventArgs is a little class that inherits EventArgs and has an Integer for the progress.
// delegate to update progress
public delegate void ProgressChangedEventHandler(Object sender, ProgressEventArgs e);
// Event added to your worker class.
public event ProgressChangedEventHandler ProgressUpdateEvent
// Method to raise the event
public void UpdateProgress(object sender, ProgressEventArgs e)
{
ProgressChangedEventHandler handler;
lock (progressUpdateEventLock)
{
handler = progressUpdateEvent;
}
if (handler != null)
handler(sender, e);
}

I would recommend you read up on the BackgroundWorker class. It is exactly for the problem you are trying to solve and makes things a lot easier than doing manual threading yourself.
Brief Example
public Form1()
{
InitializeComponent();
backgroundWorker.WorkerReportsProgress = true;
backgroundWorker.WorkerSupportsCancellation = true;
backgroundWorker.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker_ProgressChanged);
}
void backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = e.ProgressPercentage;
}
private void btnStart_Click(object sender, EventArgs e)
{
if (!backgroundWorker.IsBusy)
backgroundWorker.RunWorkerAsync();
}
private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
for (int i = 1; i < 101; ++i)
{
if (backgroundWorker.CancellationPending)
{
e.Cancel = true;
break;
}
else
{
//Sort Logic is in here.
Thread.Sleep(250);
backgroundWorker.ReportProgress(i);
}
}
}
private void btnCancel_Click(object sender, EventArgs e)
{
if (backgroundWorker.IsBusy && backgroundWorker.WorkerSupportsCancellation)
backgroundWorker.CancelAsync();
}

You could do something like this:
public delegate void StatusReporter(double progressPercentage);
public class MainClass
{
public void MainMethod()
{
Worker worker = new Worker(ReportProgress);
ThreadStart start = worker.DoWork;
Thread workThread = new Thread(start);
workThread.Start();
}
private void ReportProgress(double progressPercentage)
{
//Report here!!!
}
}
public class Worker
{
private readonly StatusReporter _reportProgress;
public Worker(StatusReporter reportProgress)
{
_reportProgress = reportProgress;
}
public void DoWork()
{
for (int i = 0; i < 100; i++ )
{
// WORK, WORK, WORK
_reportProgress(i);
}
}
}

There are a few option available to solve this sort of issue. In any case, you will have to fiddle with Invoke to get the UI to update.
You could...
...add an event that fires on your new class which your UI can listen to, and Invoke as applicable - you'd still need to pass the data to your worker class (by constructor, properties, method call, etc)
...keep the method as a method on your form, and pas that to start your new thread from (after all, a new thread doesn't have to be starting in a different class)
...change the access modifiers on your controls to be (say) internal such that any class within the same assembly can Invoke changes to the controls, or read from them.
...make your worker class a child of the form it needs to access - it can then see the privates of its parent, as long as it is passed a reference to the instance.

cross thread call

using System;
using System.Windows.Forms;
using agsXMPP;
using System.Text;
namespace iTalk2
{
public partial class Main : Form
{
agsXMPP.XmppClientConnection objXmpp;
public Main()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Console.WriteLine("Logging in. Please wait...");
Console.ReadLine();
objXmpp = new agsXMPP.XmppClientConnection();
agsXMPP.Jid jid = null;
jid = new agsXMPP.Jid("username" + "#gmail.com");
objXmpp.Password = "password";
objXmpp.Username = jid.User;
objXmpp.Server = jid.Server;
objXmpp.AutoResolveConnectServer = true;
try
{
objXmpp.OnMessage += messageReceived;
objXmpp.OnAuthError += loginFailed;
objXmpp.OnLogin += loggedIn;
objXmpp.Open();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
Console.ReadLine();
}
}
private void messageReceived(object sender, agsXMPP.protocol.client.Message msg)
{
string[] chatMessage = null;
chatMessage = msg.From.ToString().Split('/');
agsXMPP.Jid jid = null;
jid = new agsXMPP.Jid(chatMessage[0]);
agsXMPP.protocol.client.Message autoReply = null;
autoReply = new agsXMPP.protocol.client.Message(jid, agsXMPP.protocol.client.MessageType.chat, "This is a test");
objXmpp.Send(autoReply);
}
private void loginFailed(object o, agsXMPP.Xml.Dom.Element el)
{
Console.WriteLine("Login failed. Please check your details.");
}
private void loggedIn(object o)
{
Console.WriteLine("Logged in and Active.");
lblStatus.Text = "Online";
}
private void txtUsername_TextChanged(object sender, EventArgs e)
{
}
private void label1_Click(object sender, EventArgs e)
{
}
private void label2_Click(object sender, EventArgs e)
{
}
private void txtPassword_TextChanged(object sender, EventArgs e)
{
}
private void btnlogin_Click(object sender, EventArgs e)
{
}
}
}
This code is not working. the function 'loggedIn(object o)' is not working. it says the lblStatus (which is a label) is on another thread. the error window says "Cross-thread operation not valid: Control 'lblStatus' accessed from a thread other than the thread it was created on." thanks in advance.

You need to invoke a call on the UI thread. If you add code as follows at the top of the loggedIn method it should work:-
if(InvokeRequired)
{
Invoke(new Action<object>(loggedIn), o);
return;
}

WinForms is designed such that controls must only be manipulated on the UI-thread, the thread that runs the message-loop that manages the control.
Try this instead:
private void loggedIn(object o)
{
Console.WriteLine("Logged in and Active.");
Action act = () => lblStatus.Text = "Online";
Invoke(act);
}
If your application is such that this method can be called on the UI thread or a separate worker thread, you'd be better off testing forInvokeRequired(simply: am I on the control's UI thread?) and dealing with the result appropriately. For example,
private void loggedIn(object o)
{
if(InvokeRequired)
Invoke(new Action<object>(loggedIn), o);
else
{
Console.WriteLine("Logged in and Active.");
lblStatus.Text = "Online";
}
}
Note that Invokewill block until the UI-update is completed. If you want something more fire-and-forget, use BeginInvokeinstead.

When you start an application it is running from a single thread. This is the main thread, sometimes called the UI thread (since the UI will usually be rendered at startup and as a consequence it will be on that main thread.
Now, when you listen to events, your methods/delegates will get called from new threads. This is a consequence of the event based design. Normally this is not a problem unless you are trying to share data between two threads. This is exactly what happens with your UI elements. In this case your UI elements were created by your first thread but other threads are trying to update its value.
Given your design, you should check for IsInvokeRequired on the control and if so, use Invoke to set the new value. This will marshal your call from the new thread into the main thread that your UI is running on and will allow you to safely change the control.