Develop Reference

C# form, how to stop a thread with a button?

I am doing a form application in C#, it's a client that receives string with socket from server, I have a thread which runs an endless loop with inside the receive function. When I click a button I have to stop this thread, I have tried with a boolean variable but it doesn't work because the function get stuck on the receive function and the control on the boolean variable is done before when is still true. How Can I do to stop this thread?
This is the function which is runned by the thread:
public void Prova()
{
while (true)
{
string str = frmRegister.c.Receive();
... doing things...
}
}
The thread is started in this way:
public Form1()
{
InitializeComponent();
t1 = new Thread(Prova);
t1.Start();
}
And I have to stop the thread here:
private void goBack_Click(object sender, EventArgs e)
{
new Form2().Show();
this.Hide();
}
The following is my attempt with the CancellationToken:
private CancellationTokenSource tokenSource;
public void Prova(CancellationToken token)
{
while(!token.IsCancellationRequested){
while (true)
{
string str = frmRegister.c.Receive();
... doing things...
}
}
}
public Form1()
{
InitializeComponent();
tokenSource = new CancellationTokenSource();
var task = Task.Run(() => Prova(tokenSource.Token));
}
private void goBack_Click(object sender, EventArgs e)
{
tokenSource.Cancel();
new Form2().Show();
this.Hide();
}

Given your sample this should work:
private CancellationTokenSource tokenSource;
public void Prova(CancellationToken token = default)
{
while(!token.IsCancellationRequested) {
string str = frmRegister.c.Receive();
... doing things...
}
}
}
Or even:
public void Prova(CancellationToken token = default)
{
while (true)
{
token.ThrowIfCancellationRequested();
string str = frmRegister.c.Receive();
... doing things...
}
}
Or:
public void Prova(CancellationToken token = default)
{
while (true)
{
if(token.IsCancellationRequested)
return;
string str = frmRegister.c.Receive();
... doing things...
}
}
Basically get rid of the double while loop and it works.

Why did you use Thread instead of Task?
In your case
Thread th;
CancellationTokenSource cts = new CancellationTokenSource();
public void Prova(CancellationToken cancellationToken)
{
while (true)
{
cancellationToken.ThrowIfCancellationRequested();
string str = frmRegister.c.Receive();
... doing things...
}
}
public Form1()
{
InitializeComponent();
th = new Thread(() => { Prova(cts.Token); });
th.Start();;
}
private void goBack_Click(object sender, EventArgs e)
{
cts.Cancel();
}
With task
Task th;
CancellationTokenSource cts = new CancellationTokenSource();
public void Prova(CancellationToken cancellationToken)
{
while (true)
{
cancellationToken.ThrowIfCancellationRequested();
...process
}
}
public Form1()
{
InitializeComponent();
th = Task.Run(() => { Prova(cts.Token); }, cts.Token);
th.Start(); ;
}
private void goBack_Click(object sender, EventArgs e)
{
cts.Cancel();
}

"Cross-thread operation not valid" inside foreach [duplicate]

This question already has answers here:
Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on
(22 answers)
Closed 3 years ago.
I'm trying to load data to a combobox and it's working when i run the form without debugging. But when i try to run it with debug mode I get an error :System.InvalidOperationException: 'Cross-thread operation not valid: Control 'ResultBox' accessed from a thread other than the thread it was created on.'
How can I fix this? And btw a have a background worker that writes the message when the data is downloaded. I read somewhere that this issue can be fixed using backgroundworker. Here is the form code:
public Form1()
{
InitializeComponent();
backgroundWorker1.WorkerReportsProgress = true;
}
private void Form1_Load(object sender, EventArgs e)
{
backgroundWorker1.RunWorkerAsync();
}
private Task GetDataTask() {
return Task.Factory.StartNew(() => {
List<Result> results = new List<Result>();
results =
GetResults.GetData("http://worldcup.sfg.io/teams/results/");
foreach (var result in results)
{
ResultBox.Items.Add(result.Fifa_Code);
}
});
}
private void ResultBox_SelectedIndexChanged(object sender, EventArgs e)
{
}
private void SaveTeam_Click(object sender, EventArgs e)
{
}
private async void backgroundWorker1_DoWork(object sender,
DoWorkEventArgs e)
{
await GetDataTask();
}
private void backgroundWorker1_ProgressChanged(object sender,
ProgressChangedEventArgs e)
{
resultsLoadedLabel.Text = (e.ProgressPercentage.ToString() + "%");
}
private void backgroundWorker1_RunWorkerCompleted(object sender,
RunWorkerCompletedEventArgs e)
{
resultsLoadedLabel.Text = "Podaci učitani!";
}
This line of code inside foreach gets the exception :
ResultBox.Items.Add(result.Fifa_Code);
This is the class that gets results:
public class GetResults
{
public static List<Result> GetData(string url) {
var client = new RestClient();
var request = new RestRequest(url, Method.GET);
request.AddHeader("User-Agent", "Nothing");
IRestResponse<List<Result>> results = client.Execute<List<Result>>
(request);
return results.Data;
}
}

If going async, then go async all the way. RestSharp allows you to make async calls
So you can refactor data access to
public class GetResults {
public static async Task<List<Result>> GetDataAsync(string url) {
var client = new RestClient();
var request = new RestRequest(url, Method.GET);
request.AddHeader("User-Agent", "Nothing");
IRestResponse<List<Result>> results = await client.ExecuteTaskAsync<List<Result>>(request);
return results.Data;
}
}
Next, since the form load is an event handler, you can make that async as well and load the data.
public Form1() {
InitializeComponent();
}
private async void Form1_Load(object sender, EventArgs e) {
//On UI thread
resultsLoadedLabel.Text = "Loading data!";
//get data on separate thread (non blocking)
List<Result> results = await GetResults.GetDataAsync("http://worldcup.sfg.io/teams/results/");
//Back on UI thread
resultsLoadedLabel.Text = "Podaci učitani!";
foreach (var result in results) {
ResultBox.Items.Add(result.Fifa_Code);
}
}
Making sure when accessing UI controls while using async calls that they are accessed on the main thread that created them (see comments).

Using BackgroundWorker to complete two methods one after the other WPF/C#

In my program I have two methods that takes a while to complete, about few minutes each. While these methods are being executed, I display a Progress Bar in a separate window which shows the progress of each method. My two methods are in a static Utility class. They look like the following:
public static class Utility
{
public static bool TimeConsumingMethodOne(object sender)
{
for (int i = 1; i <= 100; i++)
{
Thread.Sleep(100);
(sender as BackgroundWorker).ReportProgress(i);
}
return true;
}
public static bool TimeConsumingMethodTwo(object sender)
{
for (int i = 1; i <= 100; i++)
{
Thread.Sleep(50);
(sender as BackgroundWorker).ReportProgress(i);
}
return true;
}
}
Reading through similar questions in SO I learned that I should use BackgroundWorker and used the RunWorkerCompleted() to see when the worker completes its work. So in my Main() I used BackgroundWorer() and subscribed to the RunWorkerCompleted() method. My goal here is to run the TimeConsumingMethodOne() first (and display progress while running), then once finished, run TimeConsumingMethodTwo() and show progress again, and when that's completed output the message box (which simulates some other work in my program). My Main() looks like the following:
public partial class MainWindow : Window
{
public enum MethodType
{
One,
Two
}
private BackgroundWorker worker = null;
private AutoResetEvent _resetEventOne = new AutoResetEvent(false);
private AutoResetEvent _resetEventTwo = new AutoResetEvent(false);
private ProgressBarWindow pbWindowOne = null;
private ProgressBarWindow pbWindowTwo = null;
public MainWindow()
{
InitializeComponent();
}
private void btnRun_Click(object sender, RoutedEventArgs e)
{
RunMethodCallers(sender, MethodType.One);
_resetEventOne.WaitOne();
RunMethodCallers(sender, MethodType.Two);
_resetEventTwo.WaitOne();
MessageBox.Show("COMPLETED!");
}
private void RunMethodCallers(object sender, MethodType type)
{
worker = new BackgroundWorker();
worker.WorkerReportsProgress = true;
switch (type)
{
case MethodType.One:
worker.DoWork += MethodOneCaller;
worker.ProgressChanged += worker_ProgressChangedOne;
worker.RunWorkerCompleted += worker_RunWorkerCompletedOne;
break;
case MethodType.Two:
worker.DoWork += MethodTwoCaller;
worker.ProgressChanged += worker_ProgressChangedTwo;
worker.RunWorkerCompleted += worker_RunWorkerCompletedTwo;
break;
}
worker.RunWorkerAsync();
}
private void MethodOneCaller(object sender, DoWorkEventArgs e)
{
Dispatcher.Invoke(() =>
{
pbWindowOne = new ProgressBarWindow("Running Method One");
pbWindowOne.Owner = this;
pbWindowOne.Show();
});
Utility.TimeConsumingMethodOne(sender);
}
private void MethodTwoCaller(object sender, DoWorkEventArgs e)
{
Dispatcher.Invoke(() =>
{
pbWindowTwo = new ProgressBarWindow("Running Method Two");
pbWindowTwo.Owner = this;
pbWindowTwo.Show();
});
Utility.TimeConsumingMethodTwo(sender);
}
private void worker_RunWorkerCompletedOne(object sender, RunWorkerCompletedEventArgs e)
{
_resetEventOne.Set();
}
private void worker_RunWorkerCompletedTwo(object sender, RunWorkerCompletedEventArgs e)
{
_resetEventTwo.Set();
}
private void worker_ProgressChangedOne(object sender, ProgressChangedEventArgs e)
{
pbWindowOne.SetProgressUpdate(e.ProgressPercentage);
}
private void worker_ProgressChangedTwo(object sender, ProgressChangedEventArgs e)
{
pbWindowTwo.SetProgressUpdate(e.ProgressPercentage);
}
}
Now the problem I have is, when I use _resetEventOne.WaitOne(); the UI hangs. If I removed those two waits, both methods run asynchronously and the execution moves on and outputs the MessageBox even before those two methods complete.
What am I doing wrong? How do I get the program to finish my first BackgroundWorker and then move onto the next, and then when that's done, output the MessageBox?

Now the problem I have is, when I use _resetEventOne.WaitOne(); the UI hangs. If I removed those two waits, both methods run asynchronously and the execution moves on and outputs the MessageBox even before those two methods complete.
What am I doing wrong?
When you call WaitOne(), you are blocking the UI thread, causing the UI to hang. If you remove that call, then of course you start both workers at once.
There are several different ways to approach your question. One is to stick as closely to your current implementation, and just fix the barest minimum to get it to work. Doing that, what you'll need to do is perform the actual next statement in the RunWorkerCompleted handler, instead of using an event to wait for the handler to execute.
That looks like this:
public partial class MainWindow : Window
{
public enum MethodType
{
One,
Two
}
private BackgroundWorker worker = null;
private ProgressBarWindow pbWindowOne = null;
private ProgressBarWindow pbWindowTwo = null;
public MainWindow()
{
InitializeComponent();
}
private void btnRun_Click(object sender, RoutedEventArgs e)
{
RunMethodCallers(sender, MethodType.One);
}
private void RunMethodCallers(object sender, MethodType type)
{
worker = new BackgroundWorker();
worker.WorkerReportsProgress = true;
switch (type)
{
case MethodType.One:
worker.DoWork += MethodOneCaller;
worker.ProgressChanged += worker_ProgressChangedOne;
worker.RunWorkerCompleted += worker_RunWorkerCompletedOne;
break;
case MethodType.Two:
worker.DoWork += MethodTwoCaller;
worker.ProgressChanged += worker_ProgressChangedTwo;
worker.RunWorkerCompleted += worker_RunWorkerCompletedTwo;
break;
}
worker.RunWorkerAsync();
}
private void MethodOneCaller(object sender, DoWorkEventArgs e)
{
Dispatcher.Invoke(() =>
{
pbWindowOne = new ProgressBarWindow("Running Method One");
pbWindowOne.Owner = this;
pbWindowOne.Show();
});
Utility.TimeConsumingMethodOne(sender);
}
private void MethodTwoCaller(object sender, DoWorkEventArgs e)
{
Dispatcher.Invoke(() =>
{
pbWindowTwo = new ProgressBarWindow("Running Method Two");
pbWindowTwo.Owner = this;
pbWindowTwo.Show();
});
Utility.TimeConsumingMethodTwo(sender);
}
private void worker_RunWorkerCompletedOne(object sender, RunWorkerCompletedEventArgs e)
{
RunMethodCallers(sender, MethodType.Two);
}
private void worker_RunWorkerCompletedTwo(object sender, RunWorkerCompletedEventArgs e)
{
MessageBox.Show("COMPLETED!");
}
private void worker_ProgressChangedOne(object sender, ProgressChangedEventArgs e)
{
pbWindowOne.SetProgressUpdate(e.ProgressPercentage);
}
private void worker_ProgressChangedTwo(object sender, ProgressChangedEventArgs e)
{
pbWindowTwo.SetProgressUpdate(e.ProgressPercentage);
}
}
That said, BackgroundWorker has been made obsolete by the newer task-based API with async and await. With some small changes to your code, it can be adapted to use that newer idiom:
public partial class MainWindow : Window
{
public enum MethodType
{
One,
Two
}
private ProgressBarWindow pbWindowOne = null;
private ProgressBarWindow pbWindowTwo = null;
public MainWindow()
{
InitializeComponent();
}
private async void btnRun_Click(object sender, RoutedEventArgs e)
{
await RunMethodCallers(sender, MethodType.One);
await RunMethodCallers(sender, MethodType.Two);
MessageBox.Show("COMPLETED!");
}
private async Task RunMethodCallers(object sender, MethodType type)
{
IProgress<int> progress;
switch (type)
{
case MethodType.One:
progress = new Progress<int>(i => pbWindowOne.SetProgressUpdate(i));
await Task.Run(() => MethodOneCaller(progress));
break;
case MethodType.Two:
progress = new Progress<int>(i => pbWindowTwo.SetProgressUpdate(i));
await Task.Run(() => MethodTwoCaller(progress));
break;
}
}
private void MethodOneCaller(IProgress<int> progress)
{
Dispatcher.Invoke(() =>
{
pbWindowOne = new ProgressBarWindow("Running Method One");
pbWindowOne.Owner = this;
pbWindowOne.Show();
});
Utility.TimeConsumingMethodOne(progress);
}
private void MethodTwoCaller(IProgress<int> progress)
{
Dispatcher.Invoke(() =>
{
pbWindowTwo = new ProgressBarWindow("Running Method Two");
pbWindowTwo.Owner = this;
pbWindowTwo.Show();
});
Utility.TimeConsumingMethodTwo(progress);
}
}
To do the above does require a small adjustment to the Utility class as well:
static class Utility
{
public static bool TimeConsumingMethodOne(IProgress<int> progress)
{
for (int i = 1; i <= 100; i++)
{
Thread.Sleep(100);
progress.Report(i);
}
return true;
}
public static bool TimeConsumingMethodTwo(IProgress<int> progress)
{
for (int i = 1; i <= 100; i++)
{
Thread.Sleep(50);
progress.Report(i);
}
return true;
}
}
That is, the Progress<T> class takes the place of the BackgroundWorker.ProgressChanged event and ReportProgress() method.
Note that with the above, the code has gotten significantly shorter, simpler, and is written in a more direct way (i.e. related statements are with each other in the same method now).
The example you gave is necessarily simplified. That's perfectly fine, but it does mean that it's not known here what the Thread.Sleep() method represents. In fact, in many cases, this sort of thing can be refactored further such that only the long-running work is done asynchronously. This can sometimes simplify the progress-reporting even further, because it can be done after await-ing each individual asynchronously-executed work component.
For example, let's suppose the work in the loop is either inherently asynchronous or is costly enough that it's reasonable to use Task.Run() to execute each loop iteration. For the purpose of the same, that can be represented using Task.Delay():
static class Utility
{
public static async Task<bool> TimeConsumingMethodOne(Action<int> progress)
{
for (int i = 1; i <= 100; i++)
{
await Task.Delay(100);
progress(i);
}
return true;
}
public static async Task<bool> TimeConsumingMethodTwo(Action<int> progress)
{
for (int i = 1; i <= 100; i++)
{
await Task.Delay(50);
progress(i);
}
return true;
}
}
In the above, I also don't use Progress<T>. Just a simple Action<int> delegate for the caller to use however they want.
And with that change, your window code gets even simpler:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private async void btnRun_Click(object sender, RoutedEventArgs e)
{
await MethodOneCaller();
await MethodTwoCaller();
MessageBox.Show("COMPLETED!");
}
private async Task MethodOneCaller()
{
ProgressBarWindow pbWindowOne =
new ProgressBarWindow("Running Method One") { Owner = this };
pbWindowOne.Show();
await Utility.TimeConsumingMethodOne(i => pbWindowOne.SetProgressUpdate(i));
}
private async Task MethodTwoCaller()
{
ProgressBarWindow pbWindowTwo =
new ProgressBarWindow("Running Method Two") { Owner = this };
pbWindowTwo.Show();
await Utility.TimeConsumingMethodTwo(i => pbWindowTwo.SetProgressUpdate(i));
}
}
Granted, I took the opportunity to remove the MethodType enum and just call the methods directly, which shortened the code even more. But even if all you did was avoid the use of Dispatcher.Invoke(), that still simplifies the code a lot.
In addition to all that, if you were using data binding to represent the progress state instead of setting the value directly, WPF would handle the cross-thread invocation implicitly for you, so that the Progress<T> class isn't even required even if you can't refactor the Utility class code for it itself to be async.
But, those are minor refinements compared to moving away from BackgroundWorker. I recommend doing that, but whether you invest time in those further refinements is less important.

An option i prefer is to have those 2 methods in a different thread and use a while loop to check if thread is still running and if it is use Task.Delay()
EG.
private async void BlahBahBlahAsync()
{
Thread testThread = new Thread(delegate () { });
newThread = new Thread(delegate ()
{
Timeconsuming();
});
newThread.Start();
while (testThread.IsAlive)
{
await Task.Delay(50);
}
}
private void Timeconsuming()
{
// stuff that takes a while
}

Creating a timer winform application using only delegates and events [WITHOUT TIMER OBJECT]

While using timers, stopwatches and threads is the standard way, I was wondering if there was a way to create a Winform Application in c# which had a label with initial value as 0 and which automatically kept on incrementing once a button is clicked and when the same button is clicked again it should pause. Personally, I feel that the trick is to use multicast delegates. But I am stuck as to how to proceed.
NOTE: Possible use of method callback and InvokeRequired().

this code dose not use timer or stopwatch.
i have wrote a simple class for you, forgive me if its not so standard because im so lazy for now :)
public partial class Form1 : Form
{
CancellationTokenSource src;
CancellationToken t;
public Form1()
{
InitializeComponent();
}
//start incrementing
private async void button1_Click(object sender, EventArgs e)
{
this.Start.Enabled = false;
this.Cancel.Enabled = true;
this.src = new CancellationTokenSource();
this.t = this.src.Token;
try
{
while (true)
{
var tsk = Task.Factory.StartNew<int>(() =>
{
Task.Delay(500);
var txt = int.Parse(this.Display.Text) + 1;
return (txt);
}, this.t);
var result = await tsk;
this.Display.Text = result.ToString();
}
}
catch (Exception ex)
{
return;
}
}
// Stop incrementing
private void button1_Click_1(object sender, EventArgs e)
{
this.src.Cancel();
this.Cancel.Enabled = true;
this.Start.Enabled = true;
}
}

Really not sure why you think this can be done with your restrictions in place. If you want a delay in-between your "events", then you need to use some kind of Timer, or some kind of thread (classic Thread or some kind of Task) that has a delay within it...no way around that.
Here's another approach that'll probably violate your restrictions:
public partial class Form1 : Form
{
private Int64 value = -1;
private bool Paused = true;
private int IntervalInMilliseconds = 100;
private System.Threading.ManualResetEvent mre = new System.Threading.ManualResetEvent(false);
public Form1()
{
InitializeComponent();
this.Shown += Form1_Shown;
}
private async void Form1_Shown(object sender, EventArgs e)
{
await Task.Run(delegate ()
{
while (true)
{
value++;
label1.Invoke((MethodInvoker)delegate ()
{
label1.Text = value.ToString();
});
System.Threading.Thread.Sleep(IntervalInMilliseconds);
mre.WaitOne();
}
});
}
private void button1_Click(object sender, EventArgs e)
{
if (Paused)
{
mre.Set();
}
else
{
mre.Reset();
}
Paused = !Paused;
}
}

USE an EVENT.
If you can not use timers or threads, then how about creating a do while loop that executes an event.
Some PSEUDO code is below - it should give you the idea..
bool IWantEvents = false;
public event EventHandler<myHandler> myNonTimerEvent ;
FormStart()
{
this.myNonTimerEvent += new MyNonTimerEventHandler();
IWantEvents = true;
Do
{
.. do some weird stuff - set IWantEvents False on condition ..
}
while(IWantEvents)
}
MyNonTimerEventHandler()
{
.. Do what I would do if I was using a timer event.
}

Convert method to return a task

How can I turn the below method into the right format for returning a task items. The method stub requires a task to be used. This is my first time into async methods I am using it for the windows phone 8 like below:
private System.Threading.Tasks.Task listView_PullToRefreshRequested(object sender, EventArgs e)
{
Populatelist();
}
public async void Populatelist()
{
try
{
curoListsDal _db = new curoListsDal();
cLists = await _db.GetListsAync();
listView.ItemsSource = cLists;
}
catch (Exception ex)
{
}
}

The right format would be to return a Task instead of void in PopulateListAsync and await on that inside your event handler:
private async void PullToRefreshRequestAsync(object sender, EventArgs e)
{
await PopulateListAsync();
}
public async Task PopulateListAsync()
{
curoListsDal db = new curoListsDal();
listView.ItemsSource = await db.GetListsAsync();
}
Side note: don't swallow exceptions.