I have a loop that I would like to stop using a button.
Edited for better understanding:
I do realize that you cannot stop a button while a loop was running since it will not work as long as that current UI is running. What I'm really asking for is the most efficient way of creating a thread or using BGWorker to stop this. I have seen some methods, but most of them are for Java and not C#.
What I would like to do is:
private void start_Click(object sender, EventArgs e)
{
for(int i = 0; i < nums; i++)
{
doSomething();
}
}
private void stop_Click(object sender, EventArgs e)
{
stops start_Click()
}
You can't do that. For starters, the for loop is running synchronously on the UI thread, which means you won't even be able to click the "Stop" button.
Hence, you need to move the operations of the for loop onto another thread, which means you likely won't be using a for loop at all. You need to think about how the code inside actually needs to be executed, then based on how you are doing the processing, you can implement the "Stop" button.
A very simple way to do this would be to just:
new Thread(() =>
{
int i = 0;
while (!stop && i < num)
{
doSomething();
i++;
}
}).Start();
And set stop to stop the processing loop. In a more realistic scenario, you could queue up functions that you want to process, then stop dequeuing via a similar method. Unfortunately, its hard to reccommend a setup without knowing more details.
Any solution based on your code will also have the problem of the current doSomething() completing execution (which could take a while). Again, without more info, its hard to say what the best approach to fixing that is.
To keep your UI responsive to be able to cancel the running operation you can use a backgrounworker.
The backgroundworker does the work in an other thread while keeping your UI responsive:
private readonly BackgroundWorker _backgroundWorker;
public Form1()
{
InitializeComponent();
_backgroundWorker = new BackgroundWorker
{
WorkerSupportsCancellation = true
};
_backgroundWorker.DoWork += backgroundWorker_DoWork;
_backgroundWorker.RunWorkerCompleted += backgroundWorker_RunWorkerCompleted;
Disposed += Form1_Disposed;
}
private void Form1_Disposed(object sender, EventArgs e)
{
_backgroundWorker.Dispose();
}
private void StartLoop()
{
if ( !_backgroundWorker.IsBusy )
{
_backgroundWorker.RunWorkerAsync();
}
}
private void StopLoop()
{
_backgroundWorker.CancelAsync();
}
private void backgroundWorker_DoWork( object sender , DoWorkEventArgs e )
{
var backgroundWorker = ( BackgroundWorker ) sender;
for ( var i = 0; i < 100; i++ )
{
if ( backgroundWorker.CancellationPending )
{
e.Cancel = true;
return;
}
// Do Work
}
}
private void backgroundWorker_RunWorkerCompleted( object sender , RunWorkerCompletedEventArgs e )
{
if ( e.Cancelled )
{
// handle cancellation
}
if ( e.Error != null )
{
// handle error
}
// completed without cancellation or exception
}
IMHO, it's likely the best approach here is to convert your work to an asynchronous operation and then use the async/await idiom for the loop. E.g.:
private bool _stopLoop;
private async void start_Click(object sender, EventArgs e)
{
_stopLoop = false;
for(int i = 0; i < nums && !_stopLoop; i++)
{
await Task.Run(() => doSomething());
}
}
private void stop_Click(object sender, EventArgs e)
{
_stopLoop = true;
}
This allows the loop itself to execute in the UI thread where the _stopLoop variable is being managed, but without actually blocking the UI thread (which among other things would prevent the "Stop" button from being clicked).
Unfortunately, you didn't provide details about how doSomething() works. It's possible there's a good way to convert that whole method to be an async method, but I can't comment on that without the actual code.
Note that this approach will only interrupt the loop at a point in between each operation. If you want to be able to interrupt the doSomthing() operation itself, you'll have to provide a mechanism for that. One likely approach would be to use CancellationSource and CancellationToken, which provides a convenient way to express cancellation semantics.
Try using an async/await approach. It's quite easy!
public partial class MyForm : Form
{
public MyForm()
{
InitializeComponent();
}
private CancellationTokenSource _tokenSource;
private async void start_Click(object sender, EventArgs e)
{
if (_tokenSource != null)
return;
_tokenSource = new CancellationTokenSource();
var ct = _tokenSource.Token;
await Task.Factory.StartNew(() =>
{
for (; ; )
{
if (ct.IsCancellationRequested)
break;
doSomething();
}
}, ct);
_tokenSource = null;
}
private int _labelCounter;
private void doSomething()
{
// do something
Invoke((Action)(() =>
{
myLabel.Text = (++_labelCounter).ToString();
}));
}
private void stop_Click(object sender, EventArgs e)
{
if (_tokenSource == null)
return;
_tokenSource.Cancel();
}
}
try this :
bool stop=false;
private void start_Click(object sender, EventArgs e)
{
for(int i = 0; i < nums&& !bool; i++)
{
doSomething();
}
}
and in the click event
set
stop=true;
Related
I have c# application which having 2 buttons. First having for loop which is run 10k times. and each loop code execution take 1 second to finish.
for(int i=0;i<10000;i++){
//My running code take 1 sec for each loop
}
some time i want to stop this loop/ execution on click on another button "Stop", but its not working. Please suggest me what solution.
It's not good practice to run long running operations in UI Thread (thread where all UI events are handled - such as button click). You should run your loop in another that.
You can use Task Parallel Library (TPL):
private bool stopIt = false;
private void Form1_Load(object sender, EventArgs e)
{
Task task = Task.Factory.StartNew(() =>
{
for (int i = 0; i < 1000000000; i++)
{
if (!stopIt)
{
Console.WriteLine("Here is " + i);
}
else
{
break;
}
}
});
}
private void button1_Click(object sender, EventArgs e)
{
stopIt = true;
}
The simplest solution (not best) is to add Application.DoEvents() into the loop to process button events:
private bool cancel;
public void loop()
{
for(int i=0;i<10000;i++){
//My running code take 1 sec for each loop
Application.DoEvents();
if (cancel)
break;
}
}
public void cancelButton_Click(object sender, EventArgs e)
{
cancel=true;
}
Much better and still simple solution is to employ async Task (the rest of the code stays the same minus Application.DoEvents() call):
private void loopButton_Click(object sender, EventArgs e)
{
new Task(loop).Start();
}
Beware that you should use this.Invoke(new Action(() => { <your code> } )); to access UI controls from the loop in this case.
Is it bad practice to write code like this. What I want to accomplish is that a user can press a button on a control. The button starts some kind of analyzing process and for each item done it shows a result to the user.
private IEnumerable<int> AnalyzeItems() {
for(int i = 0; i < 1000; i++) {
Thread.Sleep(500);
yield return i;
}
}
private void PerformTask_Click(object sender, EventArgs e) {
Task.Run(() => {
foreach (var item in AnalyzeItems()) {
ResultLog.Invoke((Action)delegate() { ResultLog.Text += item.ToString(); });
}
});
}
why do not use Backgroundworker?
First setup the backgroundworker properties to:
WorkerReportsProgress = true
WorkerSupportsCancellation = true
This is the code:
public partial class Form1 : Form {
public Form1() {
InitializeComponent();
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) {
for (int i = 0; i < 1000; i++) {
Thread.Sleep(500);
if (backgroundWorker1.CancellationPending) {
e.Cancel = true;
break;
}
backgroundWorker1.ReportProgress(i / 10, "step " + i);
}
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e) {
label1.Text = e.UserState.ToString();
progressBar1.Value = e.ProgressPercentage;
}
private void button1_Click(object sender, EventArgs e) {
cancelButton.Focus();
button1.Enabled = false;
backgroundWorker1.RunWorkerAsync();
}
private void cancelButton_Click(object sender, EventArgs e) {
backgroundWorker1.CancelAsync();
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {
button1.Enabled = true;
if (e.Error != null) {
MessageBox.Show(e.Error.Message, "Unexpected error");
}
if (e.Cancelled) {
MessageBox.Show("Process stopped by the user", "Cancelled");
}
label1.Text = "Press start";
progressBar1.Value = progressBar1.Minimum;
}
}
Is your approach bad practice? It depends.
If you don't expect your code inside Task.Run to throw any exceptions and you want to continue doing something else, then your code is ok. However, if you want to capture any possible exceptions and wait for the process to finish without freezing UI, then you might want to consider using async/await.
private async void PerformTask_Click(object sender, EventArgs e) {
try
{
await Task.Run(() => {
foreach (var item in AnalyzeItems()) {
ResultLog.Invoke((Action)delegate() { ResultLog.Text += item.ToString(); });
}
});
}
catch(Exception ex)
{
// handle...
}
}
Alternative approach would be to use IProgress<T>. This allows for easy separation of long running work and updating UI. Please note that you shouldn't call this method too often, because
This will put too much work on UI thread resulting in UI freeze.
If you pass any valuetype to IProgress<T>.Report method, then it gets copied. If you call this too often, you risk running garbage collector very often resulting in even bigger freezes.
All of this means that you should utilize IProgress only for truly long running work.
Now that we have it all out of the way, here is a sample of how you could notify users about progress of analyzed items:
private double _currentProgress;
public double CurrentProgress {
get => _currentProgress;
set
{
_currentProgress = value;
NotifyPropertyChanged();
}
}
private async void PerformTask_Click(object sender, EventArgs e)
{
var progress = new Progress<double>();
progress.ProgressChanged += (sender, p) => CurrentProgress = p;
await Task.Run(() => AnalyzeItems(Enumerable.Range(0, 5000).ToList(), progress));
}
private void AnalyzeItems(List<int> items, IProgress<double> progress)
{
for (int itemIndex = 0; itemIndex < items.Count; itemIndex++)
{
// Very long running CPU work.
// ...
progress.Report((double)itemIndex * 100 / items.Count);
}
}
If AnalyzeItems takes less than 100 ms for individual item, then you don't want to report after every finished item (see why above). You can decide how often you want to update status like this:
private void AnalyzeItems(List<int> items, IProgress<double> progress)
{
var lastReport = DateTime.UtcNow;
for (int itemIndex = 0; itemIndex < items.Count; itemIndex++)
{
// Very long running work.
Thread.Sleep(10);
// Tell the user what the current status is every 500 milliseconds.
if (DateTime.UtcNow - lastReport > TimeSpan.FromMilliseconds(500))
{
progress.Report((double)itemIndex * 100 / items.Count);
lastReport = DateTime.UtcNow;
}
}
}
If you have really a lot of very fast iterations, you may want to consider changing DateTime.Now to something else.
Good morning, I'm trying to write an application that use in his interface a progressbar (in C#, WPF). I have read about the need of perform the UI task in a different thread, using Backgroundworker. I trying to make it work using a lot of information, but nothing happens (the program work fine, but the progressbar only shown at the end of the "hard-work tasks").
I'm civil engineer (not a software one), so I ask if anyone can help me with that.
namespace SAP2000___Quake_Definitions
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
private readonly BackgroundWorker bgWoker = new BackgroundWorker();
public MainWindow()
{
InitializeComponent();
this.bgWoker.WorkerReportsProgress = true;
this.bgWoker.WorkerSupportsCancellation = true;
this.bgWoker.DoWork += bgWorker_DoWork;
this.bgWoker.ProgressChanged += bgWorker_ProgressChanged;
this.bgWoker.RunWorkerCompleted += bgWorker_RunWorkerCompleted;
}
private void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.progBar.Value = e.ProgressPercentage;
}
private void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker bgWorker = (BackgroundWorker)sender;
Dispatcher.Invoke(new Action(() => DoTheHardWork()));
}
private void processButton_Click(object sender, RoutedEventArgs e)
{
this.bgWoker.RunWorkerAsync();
}
private void DoTheHardWork()
{
switch (this.chckBox2.IsChecked.GetValueOrDefault())
{
case true:
this.bgWoker.ReportProgress(0);
//more hardwork with inputs from WPF
case false:
this.bgWoker.ReportProgress(0);
//more hardwork with inputs from WPF
}
}
}
}
That is not how you should be using a BackgroundWorker. I wrote some example code a few years back. It should get you on the right track:
#region Primenumbers
private void btnPrimStart_Click(object sender, EventArgs e)
{
if (!bgwPrim.IsBusy)
{
//Prepare ProgressBar and Textbox
int temp = (int)nudPrim.Value;
pgbPrim.Maximum = temp;
tbPrim.Text = "";
//Start processing
bgwPrim.RunWorkerAsync(temp);
}
}
private void btnPrimCancel_Click(object sender, EventArgs e)
{
if (bgwPrim.IsBusy)
{
bgwPrim.CancelAsync();
}
}
private void bgwPrim_DoWork(object sender, DoWorkEventArgs e)
{
int highestToCheck = (int)e.Argument;
//Get a reference to the BackgroundWorker running this code
//for Progress Updates and Cancelation checking
BackgroundWorker thisWorker = (BackgroundWorker)sender;
//Create the list that stores the results and is returned by DoWork
List<int> Primes = new List<int>();
//Check all uneven numbers between 1 and whatever the user choose as upper limit
for(int PrimeCandidate=1; PrimeCandidate < highestToCheck; PrimeCandidate+=2)
{
//Report progress
thisWorker.ReportProgress(PrimeCandidate);
bool isNoPrime = false;
//Check if the Cancelation was requested during the last loop
if (thisWorker.CancellationPending)
{
//Tell the Backgroundworker you are canceling and exit the for-loop
e.Cancel = true;
break;
}
//Determin if this is a Prime Number
for (int j = 3; j < PrimeCandidate && !isNoPrime; j += 2)
{
if (PrimeCandidate % j == 0)
isNoPrime = true;
}
if (!isNoPrime)
Primes.Add(PrimeCandidate);
}
//Tell the progress bar you are finished
thisWorker.ReportProgress(highestToCheck);
//Save Return Value
e.Result = Primes.ToArray();
}
private void bgwPrim_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
pgbPrim.Value = e.ProgressPercentage;
}
private void bgwPrim_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
pgbPrim.Value = pgbPrim.Maximum;
this.Refresh();
if (!e.Cancelled && e.Error == null)
{
//Show the Result
int[] Primes = (int[])e.Result;
StringBuilder sbOutput = new StringBuilder();
foreach (int Prim in Primes)
{
sbOutput.Append(Prim.ToString() + Environment.NewLine);
}
tbPrim.Text = sbOutput.ToString();
}
else
{
tbPrim.Text = "Operation canceled by user or Exception";
}
}
#endregion
You have to limit all UI writing work to the Progress Report and Run wokrer compelte Events. Those will be raised in the thread that created the BGW (wich should be the UI thread) automagically.
Note that you can only report progress between distinct steps. I had the advantage that I had to write the loop anyway. But if you have existing code (like most download or disk code), you can usually only report between files.
my mistakes were three:
Trying to use "Dispatcher.Invoke(new Action(() => DoTheHardWork()));" to solve an exception related to my thread (exception caused by point #3).
Avoiding the instantiation: BackgroundWorker bgWorker = (BackgroundWorker)sender (thank you #Christopher).
Writing a code that manipulate a UI-Component inside the DoWork event handle of my Backgroundworker. MSDN says: You must be careful not to manipulate any user-interface objects in your DoWork event handler. Instead, communicate to the user interface through the ProgressChanged and RunWorkerCompleted events. Trying this, the exception occur.
Solving the point #2 and #3, the UI is perfectly responsive respect to the "hardwork" function (runned in background).
This question already has answers here:
c# Thread issue using Invoke from a background thread
(5 answers)
Closed 6 years ago.
I can't seem to be able to kill my thread in C#. The program seems to get stuck in an infinite loop on the FormClosing event.
EDIT // I'm attempting to end the thread and close the whole program when the FormClosing event gets fired.
Here's the code:
public partial class Form1 : Form
{
private Thread thread;
private volatile bool threadRunning = true;
public Form1()
{
InitializeComponent();
}
private void Loop()
{
Console.WriteLine(threadRunning);
while (threadRunning)
{
MethodInvoker mi = delegate { timeLabel.Text = TimeWriterSingleton.Instance.OutputTime(); };
Invoke(mi);
}
}
private void Form1_Load(object sender, EventArgs e)
{
thread = new Thread(Loop);
thread.Start();
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
threadRunning = false;
thread.Join();
}
}
Your Join blocked the GUI thread, and your Invoke in the other thread is waiting for your GUI thread to process the delegate.
A quick fix would be to use BeginInvoke instead of Invoke, thus posting rather than sending the window message.
Alternatively, don't join. The purpose of that code is to clean up after yourself, why do you care when the thread dies?
A 3rd fix would be to just gut the thread, either through Thread.Abort or Environment.Exit. It might skip some clean up, but your particular code shouldn't care and the point is to exit anyway.
Edit: working code using BeginInvoke follows:
private void Loop()
{
while (threadRunning)
{
BeginInvoke(new MethodInvoker(() => timeLabel.Text = DateTime.Now.ToString()));
Thread.Sleep(100);
}
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
threadRunning = false;
thread.Join();
}
The issue with the original code is that it's running as fast as your CPU allows, filling the message queue to the point where the GUI thread can't keep up. Updating Windows controls is very expensive, compared to simply adding a number to a queue. So I added a pause between UI updates to let the GUI thread breathe.
To the downvoters, I'd be curious why you're doing it. Nothing I said is factually wrong.
I decided to switch to using a timer. The code now looks like this, and the application works:
public partial class Form1 : Form
{
private System.Timers.Timer timer;
public Form1()
{
InitializeComponent();
timer = new System.Timers.Timer(60000);
}
private void Form1_Load(object sender, EventArgs e)
{
timeLabel.Text = TimeWriterSingleton.Instance.OutputTime();
timer.Elapsed += TimerElapsed;
timer.Enabled = true;
}
private void TimerElapsed(object sender, ElapsedEventArgs e)
{
timeLabel.Text = TimeWriterSingleton.Instance.OutputTime();
}
}
Actually using the BeginInvoke() is not bad idea. It might look like that:
private void Form1_Load(object sender, EventArgs e)
{
thread = new Thread(() => Loop(this));
thread.Start();
}
private void Loop(Form1 form)
{
while (threadRunning && !form.IsDisposed)
{
MethodInvoker mi = delegate() { timeLabel.Text = /* Some text */ ; };
BeginInvoke(mi);
// Let sleep some time...
Thread.Sleep(1);
}
}
private void Form1_FormClosing_1(object sender, FormClosingEventArgs e)
{
threadRunning = false;
thread.Join();
}
I have c# application which having 2 buttons. First having for loop which is run 10k times. and each loop code execution take 1 second to finish.
for(int i=0;i<10000;i++){
//My running code take 1 sec for each loop
}
some time i want to stop this loop/ execution on click on another button "Stop", but its not working. Please suggest me what solution.
It's not good practice to run long running operations in UI Thread (thread where all UI events are handled - such as button click). You should run your loop in another that.
You can use Task Parallel Library (TPL):
private bool stopIt = false;
private void Form1_Load(object sender, EventArgs e)
{
Task task = Task.Factory.StartNew(() =>
{
for (int i = 0; i < 1000000000; i++)
{
if (!stopIt)
{
Console.WriteLine("Here is " + i);
}
else
{
break;
}
}
});
}
private void button1_Click(object sender, EventArgs e)
{
stopIt = true;
}
The simplest solution (not best) is to add Application.DoEvents() into the loop to process button events:
private bool cancel;
public void loop()
{
for(int i=0;i<10000;i++){
//My running code take 1 sec for each loop
Application.DoEvents();
if (cancel)
break;
}
}
public void cancelButton_Click(object sender, EventArgs e)
{
cancel=true;
}
Much better and still simple solution is to employ async Task (the rest of the code stays the same minus Application.DoEvents() call):
private void loopButton_Click(object sender, EventArgs e)
{
new Task(loop).Start();
}
Beware that you should use this.Invoke(new Action(() => { <your code> } )); to access UI controls from the loop in this case.