We Keep Coding

Two issues with backgroundworker with progress bar WPF

I'm using WPF and I have main thread which is GUI (wizard).
When user click Finish on wizard it open second thread which display user progress bar used in background worker.
In Main thread I doing:
MessageWithProgressBar progress = new MessageWithProgressBar();
progress.Show();
createFilesInA();
createFilesInB();
createFilesInC();
createFilesInD();
createFilesInE();
createFilesInF();
createFilesInG();
createFilesInH();
createFilesInI();
createFilesInJ();
createFilesInK();
In each createFiles method I increment by 1 the static variable called currentStep which I used it in background worker as detailed below.
In background worker I doing:
public partial class MessageWithProgressBar : Window
{
private BackgroundWorker backgroundWorker = new BackgroundWorker();
public MessageWithProgressBar()
{
InitializeComponent();
backgroundWorker.WorkerReportsProgress = true;
backgroundWorker.ProgressChanged += ProgressChanged;
backgroundWorker.DoWork += DoWork;
backgroundWorker.RunWorkerCompleted += BackgroundWorker_RunWorkerCompleted;
}
private void DoWork(object sender, DoWorkEventArgs e)
{
Thread.Sleep(100);
int i = GeneralProperties.General.currentStep;
if (i > GeneralProperties.General.thresholdStep)
{
progress.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
new DispatcherOperationCallback(delegate
{
progress.Value = 100;
title.Content = progress.Value.ToString();
return null;
}), null);
return;
}
else
{
progress.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
new DispatcherOperationCallback(delegate
{
progress.Value = (int)Math.Floor((decimal)(8 * i));
progressLabel.Text = progress.Value.ToString();
return null;
}), null);
}
}
private void ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progress.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
new DispatcherOperationCallback(delegate
{
progress.Value = e.ProgressPercentage;
return null;
}), null);
}
private void BackgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
progress.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
new DispatcherOperationCallback(delegate
{
progress.Value = 100;
title.Content = progress.Value.ToString();
return null;
}), null);
WindowMsgGenDB msg = new WindowMsgGenDB();
msg.Show();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
if (backgroundWorker.IsBusy == false)
{
backgroundWorker.RunWorkerAsync();
}
}
}
The main thread updated variable called currentStep and the second thread used it to report on the main thread progress.
The operations of the main thread takes a few seconds (not more 15 seconds)
I have two issues:
I see on progress bar only when currentStep=2 (then the progress is 16) and then the progress is 100, and I don't see every step
At the beginning, the progress bar is freeze and it seems like it stuck.
(maybe it connects to the call progress.Show() from the main thread?)
Thanks!

As far as I understand your code your background worker is not doing anything, really. It updates the progress once and that's it.
Also: using global static variables to communicate between a form and a background worker - ouch...
Also, you're using it wrong in my opinion. The work (CreateFilesInA ... CreateFilesInK) should be done by the background worker - that's what it is for. As the main thread will be blocked the way you implemented it, you will not see any updates otherwise.
The usual way to implement something like this is:
Create progress window and disable UI
Start background worker that does stuff in DoWork. In DoWork, after every call to a CreateFilesInXYZ method, call ReportProgress to the the UI be updated.
Update stuff in progress window whenever ProgressChanged event is fired
Hide progress window and enable your application's UI when background worker is done
The way you're doing it it's in no way asynchronous. So, actually, your code should look something like this:
public partial class MainWindow : Window
{
private BackgroundWorker backgroundWorker = new BackgroundWorker();
private MessageWithProgressBar progressWindow;
public MainWindow()
{
InitializeComponent();
backgroundWorker.WorkerReportsProgress = true;
backgroundWorker.ProgressChanged += ProgressChanged;
backgroundWorker.DoWork += DoWork;
backgroundWorker.RunWorkerCompleted += BackgroundWorker_RunWorkerCompleted;
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
progressWindow = new MessageWithProgressBar();
progressWindow.Owner = this;
progressWindow.Show();
backgroundWorker.RunWorkerAsync();
}
private void DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = (BackgroundWorker)sender;
int numSteps = 11;
int currentStep = 0;
int progress = 0;
CreateFilesInA();
currentStep += 1;
progress = (int)((float)currentStep / (float)numSteps * 100.0);
worker.ReportProgress(progress);
CreateFilesInB();
currentStep += 1;
progress = (int)((float)currentStep / (float)numSteps * 100.0);
worker.ReportProgress(progress);
// All other steps here
...
}
private void ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressWindow.progress.Value = e.ProgressPercentage;
}
private void BackgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
progressWindow.Close();
WindowMsgGenDB msg = new WindowMsgGenDB();
msg.Show();
}
}
Please note that the above code goes into your main window! The MessageWithProgressWindow does not contain any code. Maybe the Window_Loaded event handler is not the right place to start the background worker, but you get the picture.

Stop running backgroundworker and start new one.

I have a window with a calendar and datagrid.
When the user selects a new date in the calendar I want to query the database for calls made on that date.
public HistoryDialog()
{
InitializeComponent();
worker = new BackgroundWorker();
worker.WorkerSupportsCancellation = true;
worker.DoWork += new DoWorkEventHandler(worker_DoWork);
worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
HistoryGrid.SelectionChanged += new SelectionChangedEventHandler(HistoryGrid_SelectionChanged);
}
void calendar_SelectedDatesChanged(object sender, SelectionChangedEventArgs e)
{
startDate = calendar.SelectedDates.OrderBy(x => x.Date).FirstOrDefault();
endDate = calendar.SelectedDates.OrderByDescending(x => x.Date).FirstOrDefault();
if (endDate != startDate)
SelectedDateTextBlock.Text = String.Format("{0:d MMMM}", startDate) + " - " + String.Format("{0:d MMMM}", endDate);
else
SelectedDateTextBlock.Text = String.Format("{0:d MMMM}", startDate);
SearchInDatabase();
}
private void SearchInDatabase()
{
if (worker.IsBusy)
worker.CancelAsync();
worker.RunWorkerAsync();
}
void worker_DoWork(object sender, DoWorkEventArgs e)
{
if ((worker.CancellationPending == true))
{
e.Cancel = true;
return;
}
var CallLog = ct.GetCalllogs(startDate, endDate, userID); // Database query
e.Result = CallLog;
}
void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
IList CallLog = e.Result as IList;
foreach (CalllogInfo callInfo in CallLog)
{
chvm.CallHistoryList.Add(callInfo);
}
}
But when the user selects a new date while the backgroundworker is still running my program crashes.
How can I stop a running background worker and start a new one ?

Now I see you have set the WorkerSupportsCancellation property to true.
Now this doesnt actually cancel your BackgroundWorker it simply allows you to call the CancelAsync() method.
What you need to do is in your method processing periodically check to ensure the working is not pending cancellation from the CancellationPending property. As you check this property when you find it true you can set the Cancel property of the event arguments to true. This will then be available in your RunWorkerCompleted event. At this point (in your RunWorkerCompleted event handler) you can then restart the BackgroundWorker.
Here is an example using very basic background worker that supports cancellation and responds to the cancel request.
public MainWindow()
{
InitializeComponent();
this.DataContext = dataModel;
worker = new BackgroundWorker();
worker.WorkerSupportsCancellation = true;
worker.DoWork += (o, e) =>
{
//do a long running task
for (int i = 0; i < 10; i++)
{
System.Threading.Thread.Sleep(500);
if (worker.CancellationPending)
{
e.Cancel = true;
return;
}
}
};
worker.RunWorkerCompleted += (o, e) =>
{
if (e != null && e.Cancelled)
{
startTheWorker();
return;
}
//TODO: I AM DONE!
};
}
BackgroundWorker worker;
private void Button_Click(object sender, RoutedEventArgs e)
{
if (worker != null && worker.IsBusy)
worker.CancelAsync();
else if(worker != null && !worker.CancellationPending)
startTheWorker();
}
void startTheWorker()
{
if (worker == null)
throw new Exception("How come this is null?");
worker.RunWorkerAsync();
}
As you can see we are having to do all the work of actually cancelling the worker. Hope this helps.

In addition to the other answers, I want to add the following. The following block of code is responsible for raising the error:
private void SearchInDatabase()
{
if (worker.IsBusy)
worker.CancelAsync();
worker.RunWorkerAsync();
}
As you call CancelAsync, execution of your code is continued immediately without waiting until the BackgroundWorker is really stopped. This is the reason why RunWorkerAsync is called while the BackgroundWorker is still running resulting in the error you describe. You should change your code as follows:
private void SearchInDatabase()
{
if (worker.IsBusy)
worker.CancelAsync();
while(worker.IsBusy)
System.Threading.Thread.Sleep(100);
worker.RunWorkerAsync();
}
This assures that the BackgroundWorker finishes its work before starting a new one. In addition, you need to enhance your DoWork-method to check the CancellationPending property more often in order to really stop the BackgroundWorker soon after a cancellation request.

Your problem is coming from the cancellation.
When you are in ct.GetCalllogs your code is blocked and doesn't support cancellation.
In ct.GetCalllogs you should verify that the backgroundworker isn't in cancel state and then start again with the new value.
Here is an element of response how to stop backgroundworker correctly

Disallowing selections while the worker is doing work would remove the issue without the need to tackle it:
void calendar_SelectedDatesChanged(object sender, SelectionChangedEventArgs e)
{
// .. cut ..
// disable the calendar and go on
calendar.IsEnabled = false;
SearchInDatabase();
}
private void SearchInDatabase()
{
// No longer needed: selection processing is now "atomic"
// if (worker.IsBusy) worker.CancelAsync();
worker.RunWorkerAsync();
}
void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
// .. cut ..
calendar.IsEnabled = true;
}
Or you could bind worker.IsBusy to calendar.IsEnabled to have it handled "automagically" (while still not having to worry about concurrent executions of the worker method).

C# BackgroundWorker not working as parameter

public static void CalculateAttributions(BackgroundWorker worker, string _filename, ComboBox cmb, OpenFileDialog open)
{
worker = new BackgroundWorker { WorkerReportsProgress = true };
while (wave.Position != length)
{
...Process..
worker.ReportProgress((100 * (int)(length / wave.Position)) / (int)(length / mainBuffer.Length));
}
}
I wrote this method in a class to perform my calculations and using BackgroundWorker as parameter to show a Progressbarduring loop. However when i run this method in Form.cs
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = Math.Min(e.ProgressPercentage, 100);
}
this event is not working so ProgressBar value not changed. How can i make it work?

The report Progress event you have given here is for the backgroundworker1 and not the worker you coded within the function CalculateAttributions(...)
To enbale report progress and do progress bar changes.. Try the following code
Worker1.ProgressChanged+=new delegate {
progressBar1.Value = Math.Min(e.ProgressPercentage, 100);
};
with in the same function.
Hope this helps you

You will need to attach your event handlers. It should go like this.
public static void CalculateAttributions(BackgroundWorker worker, string _filename, ComboBox cmb, OpenFileDialog open)
{
worker = new BackgroundWorker { WorkerReportsProgress = true };
worker.DoWork += new DoWorkEventHandler(worker_DoWork);
worker.ProgressChanged += new ProgressChangedEventHandler(worker_ProgressChanged);
worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);
if (worker.IsBusy != true)
{
worker.RunWorkerAsync();
}
}
private void worker_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
while (wave.Position != length)
{
...Process..
worker.ReportProgress((100 * (int)(length / wave.Position)) / (int)(length / mainBuffer.Length));
}
}
private void worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = Math.Min(e.ProgressPercentage, 100);
}
private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
//done
}

I think you should check this link.
http://msdn.microsoft.com/en-us/library/cc221403(v=vs.95).aspx
The idea is to get your work inside background worker. and after each milestone report progress on your progress bar.
create background worker object
attach event handlers
call RunWorkerAsynch()
add code inside event handlers
do work will have the real work and report to progress call
report to progress will simply tell your progress bar to move one step ahead
completed will be called once everything is done. you may want to show a message to user that the operation is completed.

Run task asynchronously in C#

I have some process heavy tasks that run in my WinForms app. The problem is, while its running, it freeze the UI (UI main thread).
I haven't worked that much with threads and delegates in C# yet, and that's why I hope someone could help me to, how to handle those process heavy tasks, without freezing the UI, so the user don't think the app is crashing while waiting?
Eg. I have a call through my FrontController, that takes time:
_controller.testExportExcel(wrapper, saveDialog.FileName);
Since it's creating an Excel file. I won't the app to be responding on the UI while its working.
Another example of a process heavy task could be this:
private void dataGridView_liste_DataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
{
if (e.ListChangedType != ListChangedType.ItemDeleted)
{
foreach (DataGridViewRow r in dataGridView_liste.Rows)
{
DataGridViewCellStyle red = dataGridView_liste.DefaultCellStyle.Clone();
red.BackColor = Color.LightGreen;
if (r.Cells["News"].Value != null && (bool)r.Cells["News"].Value == true)
r.DefaultCellStyle = red;
}
}
}
Where the foreach loop takes time, and freeze the UI. An async thread running the process and automatically closing when its done, could be useful I think. But how does it work??

How about using a Task (if targetting .net 4)? This is considered as a replacement of the BackgroundWorker class since it supports nesting (parent/child tasks), task continuations, etc.
E.g.
private void dataGridView_liste_DataBindingComplete(object sender,
DataGridViewBindingCompleteEventArgs e)
{
Task t = Task.Factory.StartNew(() =>
{
// do your processing here - remember to call Invoke or BeginInvoke if
// calling a UI object.
});
t.ContinueWith((Success) =>
{
// callback when task is complete.
}, TaskContinuationOptions.NotOnFaulted);
t.ContinueWith((Fail) =>
{
//log the exception i.e.: Fail.Exception.InnerException);
}, TaskContinuationOptions.OnlyOnFaulted);
}

I answered a very similar question here
It boils down to using BackgroundWorker.
msdn provides an example:
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
namespace SL_BackgroundWorker_CS
{
public partial class Page : UserControl
{
private BackgroundWorker bw = new BackgroundWorker();
public Page()
{
InitializeComponent();
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
}
private void buttonStart_Click(object sender, RoutedEventArgs e)
{
if (bw.IsBusy != true)
{
bw.RunWorkerAsync();
}
}
private void buttonCancel_Click(object sender, RoutedEventArgs e)
{
if (bw.WorkerSupportsCancellation == true)
{
bw.CancelAsync();
}
}
private void bw_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
for (int i = 1; (i <= 10); i++)
{
if ((worker.CancellationPending == true))
{
e.Cancel = true;
break;
}
else
{
// Perform a time consuming operation and report progress.
System.Threading.Thread.Sleep(500);
worker.ReportProgress((i * 10));
}
}
}
private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if ((e.Cancelled == true))
{
this.tbProgress.Text = "Canceled!";
}
else if (!(e.Error == null))
{
this.tbProgress.Text = ("Error: " + e.Error.Message);
}
else
{
this.tbProgress.Text = "Done!";
}
}
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.tbProgress.Text = (e.ProgressPercentage.ToString() + "%");
}
}
}
Everything that runs in the DoWork event handler is asynchronous.
Everything that runs in ProgessChanged/RunWorkCompleted's event handlers is on the UI thread.

For your first example, a call to _controller.testExportExcel(), a BackgroundWorker or Task Parallel Library call (i.e. Task.Factory.StartNew(...)) would be appropriate to satify your requirement of keeping the UI responsive. Plenty of examples floating around, including the other answers here.
For your second example, you will find you can't put this on a background thread since it appears to be code that manipulates the UI. Specifically, if the implementation of your BackgroundWorker's DoWork event handler, or the delegate you pass to Task.Factory.StartNew(), or the method for a plain old thread touch the UI, you are highly likely (/certain?) to get an exception stating "Cross-thread operation not valid".
The reason for this is covered in this question. But I'm more surprised actually this is slow enough that you want to make it asynchronous. There might be some simple ways to make this code more responsive - Control.SuspendLayout() and .ResumeLayout() springs to mind.

WinForm Multithreading. Use backgroundWorker or not?

I have a simple app which fires of a series of data intensive tasks. I'm not very experienced with WinForms and I was wondering the best way to do this without locking the interface. Can backgroundWorker be re-used, or is there another way to do this?
Thanks

BackgroundWorker is a thread that also includes notification synchronization. For example, if you wanted to update your UI when the scan completes, a regular Thread cannot access the UI objects (only the UI thread can do that); so, BackgroundWorker provides a Completed event handler that runs on the UI thread when the operation completes.
for more info see: Walkthrough: Multithreading with the BackgroundWorker Component (MSDN)
and a simple sample code:
var worker = new System.ComponentModel.BackgroundWorker();
worker.DoWork += (sender,e) => Thread.Sleep(60000);
worker.RunWorkerCompleted += (sender,e) => MessageBox.Show("Hello there!");
worker.RunWorkerAsync();

backgroundWorker can be used.
its benefit - it allows you to update a progress bar and interact with UI controls. (WorkerReportsProgress)
Also it has a cancellation mechanism. (WorkerSupportsCancellation)

You can use BackgroundWorker for such requirements. Below is a sample which updates a label status based on percentage task [long running] completion. Also, there is a sample business class which sets some value and the value is set back to UI via ProgressChanged handler. DoWork is the place where you write your long running task logic. Copy-Paste the code below after adding a label and backgroundworker component on a Winforms app & give it a shot. You may debug across various handler [RunWorkerCompleted, ProgressChanged, DoWork] and have a look at InitWorker method. Notice the cancellation feature too.
using System.ComponentModel;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form3 : Form
{
private BackgroundWorker _worker;
BusinessClass _biz = new BusinessClass();
public Form3()
{
InitializeComponent();
InitWorker();
}
private void InitWorker()
{
if (_worker != null)
{
_worker.Dispose();
}
_worker = new BackgroundWorker
{
WorkerReportsProgress = true,
WorkerSupportsCancellation = true
};
_worker.DoWork += DoWork;
_worker.RunWorkerCompleted += RunWorkerCompleted;
_worker.ProgressChanged += ProgressChanged;
_worker.RunWorkerAsync();
}
void DoWork(object sender, DoWorkEventArgs e)
{
int highestPercentageReached = 0;
if (_worker.CancellationPending)
{
e.Cancel = true;
}
else
{
double i = 0.0d;
int junk = 0;
for (i = 0; i <= 199990000; i++)
{
int result = _biz.MyFunction(junk);
junk++;
// Report progress as a percentage of the total task.
var percentComplete = (int)(i / 199990000 * 100);
if (percentComplete > highestPercentageReached)
{
highestPercentageReached = percentComplete;
// note I can pass the business class result also and display the same in the LABEL
_worker.ReportProgress(percentComplete, result);
_worker.CancelAsync();
}
}
}
}
void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
// Display some message to the user that task has been
// cancelled
}
else if (e.Error != null)
{
// Do something with the error
}
}
void ProgressChanged(object sender, ProgressChangedEventArgs e)
{
label1.Text = string.Format("Result {0}: Percent {1}",e.UserState, e.ProgressPercentage);
}
}
public class BusinessClass
{
public int MyFunction(int input)
{
return input+10;
}
}
}

The background worker would be a good choice to start with
For more info look here
http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.aspx