Display progress bar while doing some work in C

Question

I want to display a progress bar while doing some work  but that would hang the UI and the progress bar won t update   I have a WinForm ProgressForm with a ProgressBar that will continue indefinitely in a marquee fashion   using ProgressForm p   new ProgressForm this       Do Some Work     Now there are many ways to solve the issue  like using BeginInvoke  wait for the task to complete and call EndInvoke  Or using the BackgroundWorker or Threads    I am having some issues with the EndInvoke  though that s not the question  The question is which is the best and the simplest way you use to handle such situations  where you have to show the user that the program is working and not unresponsive  and how do you handle that with simplest code possible that is efficient and won t leak  and can update the GUI   Like BackgroundWorker needs to have multiple functions  declare member variables  etc  Also you need to then hold a reference to the ProgressBar Form and dispose of it   Edit  BackgroundWorker is not the answer because it may be that I don t get the progress notification  which means there would be no call to ProgressChanged as the DoWork is a single call to an external function  but I need to keep call the Application DoEvents    for the progress bar to keep rotating   The bounty is for the best code solution for this problem  I just need to call Application DoEvents   so that the Marque progress bar will work  while the worker function works in the Main thread  and it doesn t return any progress notification  I never needed  NET magic code to report progress automatically  I just needed a better solution than    Action lt String  String gt  exec   DoSomethingLongAndNotReturnAnyNotification  IAsyncResult result   exec BeginInvoke path  parameters  null  null   while   result IsCompleted      Application DoEvents      exec EndInvoke result     that keeps the progress bar alive  means not freezing but refreshes the marque

User · Answer

And another example that BackgroundWorker is the right way to do it     using System  using System ComponentModel  using System Threading  using System Windows Forms   namespace SerialSample       public partial class Form1   Form               private BackgroundWorker  BackgroundWorker          private Random  Random           public Form1                         InitializeComponent                 ProgressBar Style   ProgressBarStyle Marquee               ProgressBar Visible   false               Random   new Random                 InitializeBackgroundWorker                       private void InitializeBackgroundWorker                          BackgroundWorker   new BackgroundWorker                 BackgroundWorker WorkerReportsProgress   true                BackgroundWorker DoWork     sender  e    gt    MethodInvoker e Argument  Invoke                 BackgroundWorker ProgressChanged     sender  e    gt                                         ProgressBar Style   ProgressBarStyle Continuous                       ProgressBar Value   e ProgressPercentage                                  BackgroundWorker RunWorkerCompleted     sender  e    gt                                if   ProgressBar Style    ProgressBarStyle Marquee                                         ProgressBar Visible   false                                                      private void buttonStart Click object sender  EventArgs e                         BackgroundWorker RunWorkerAsync new MethodInvoker      gt                                         ProgressBar BeginInvoke new MethodInvoker      gt   ProgressBar Visible   true                        for  int i   0  i  lt  1000  i                                                  Thread Sleep 10                            BackgroundWorker ReportProgress i   10

User · Answer

Indeed you are on the right track  You should use another thread  and you have identified the best ways to do that  The rest is just updating the progress bar  In case you don t want to use BackgroundWorker like others have suggested  there is one trick to keep in mind  The trick is that you cannot update the progress bar from the worker thread because UI can be only manipulated from the UI thread  So you use the Invoke method  It goes something like this  fix the syntax errors yourself  I m just writing a quick example    class MyForm  Form       private void delegate UpdateDelegate int Progress        private void UpdateProgress int Progress                if   this InvokeRequired               this Invoke  UpdateDelegate UpdateProgress  Progress           else             this MyProgressBar Progress   Progress            The InvokeRequired property will return true on every thread except the one that owns the form  The Invoke method will call the method on the UI thread  and will block until it completes  If you don t want to block  you can call BeginInvoke instead

User · Answer

For me the easiest way is definitely to use a BackgroundWorker  which is specifically designed for this kind of task  The ProgressChanged event is perfectly fitted to update a progress bar  without worrying about cross-thread calls

User · Answer

Re  Your edit  You need a BackgroundWorker or Thread to do the work  but it must call ReportProgress   periodically to tell the UI thread what it is doing  DotNet can t magically work out how much of the work you have done  so you have to tell it  a  what the maximum progress amount you will reach is  and then  b  about 100 or so times during the process  tell it which amount you are up to   If you report progress fewer than 100 times  the progess bar will jump in large steps  If you report more than 100 times  you will just be wasting time trying to report a finer detail than the progress bar will helpfully display   If your UI thread can happily continue while the background worker is running  then your work is done   However  realistically  in most situations where the progress indication needs to be running  your UI needs to be very careful to avoid a re-entrant call  e g  If you are running a progress display while exporting data  you don t want to allow the user to start exporting data again while the export is in progress   You can handle this in two ways    The export operation checks to see if the background worker is running  and disabled the export option while it is already importing  This will allow the user to do anything at all in your program except exporting - this could still be dangerous if the user could  for example  edit the data that is being exported  Run the progress bar as a  modal  display so that your program reamins  alive  during the export  but the user can t actually do anything  other than cancel  until the export completes  DotNet is rubbish at supporting this  even though it s the most common approach  In this case  you need to put the UI thread into a busy wait loop where it calls Application DoEvents   to keep message handling running  so the progress bar will work   but you need to add a MessageFilter that only allows your application to respond to  safe  events  e g  it would allow Paint events so your application windows continue to redraw  but it would filter out mouse and keyboard messages so that the user can t actually do anything in the proigram while the export is in progress  There are also a couple of sneaky messages you ll need to pass through to allow the window to work as normal  and figuring these out will take a few minutes - I have a list of them at work  but don t have them to hand here I m afraid  It s all the obvious ones like NCHITTEST plus a sneaky  net one  evilly in the WM USER range  which is vital to get this working     The last  gotcha  with the awful dotNet progress bar is that when you finish your operation and close the progress bar you ll find that it usually exits when reporting a value like  80    Even if you force it to 100  and then wait for about half a second  it still may not reach 100   Arrrgh  The solution is to set the progress to 100   then to 99   and then back to 100  - when the progress bar is told to move forwards  it animates slowly towards the target value  But if you tell it to go  backwards   it jumps immediately to that position  So by reversing it momentarily at the end  you can get it to actually show the value you asked it to show

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There s a load of information about threading with  NET C  on Stackoverflow  but the article that cleared up windows forms threading for me was our resident oracle  Jon Skeet s  quot Threading in Windows Forms quot   The whole series is worth reading to brush up on your knowledge or learn from scratch  I m impatient  just show me some code As far as  quot show me the code quot  goes  below is how I would do it with C  3 5  The form contains 4 controls   a textbox a progressbar 2 buttons   quot buttonLongTask quot  and  quot buttonAnother quot   buttonAnother is there purely to demonstrate that the UI isn t blocked while the count-to-100 task is running  public partial class Form1   Form       public Form1                 InitializeComponent               private void buttonLongTask Click object sender  EventArgs e                Thread thread   new Thread LongTask           thread IsBackground   true          thread Start               private void buttonAnother Click object sender  EventArgs e                textBox1 Text    quot Have you seen this  quot              private void LongTask                 for  int i   0  i  lt  100  i                          Update1 i               Thread Sleep 500                        public void Update1 int i                if  InvokeRequired                        this BeginInvoke new Action lt int gt  Update1   new object     i                 return                     progressBar1 Value   i

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We are use modal form with BackgroundWorker for such a thing   Here is quick solution     public class ProgressWorker lt TArgument gt    BackgroundWorker where TArgument   class                public Action lt TArgument gt  Action   get  set             protected override void OnDoWork DoWorkEventArgs e                        if  Action  null                                Action e Argument as TArgument                                   public sealed partial class ProgressDlg lt TArgument gt    Form where TArgument   class       private readonly Action lt TArgument gt  action       public Exception Error   get  set         public ProgressDlg Action lt TArgument gt  action                if  action    null  throw new ArgumentNullException  action            this action   action            InitializeComponent              MaximumSize   Size          MaximizeBox   false          Closing    new System ComponentModel CancelEventHandler ProgressDlg Closing             public string NotificationText               set                       if  value  null                                Invoke new Action lt string gt  s   gt  Text   value                                         void ProgressDlg Closing object sender  System ComponentModel CancelEventArgs e                FormClosingEventArgs args    FormClosingEventArgs e          if  args CloseReason    CloseReason UserClosing                        e Cancel   true                         private void ProgressDlg Load object sender  EventArgs e                    public void RunWorker TArgument argument                System Windows Forms Application DoEvents            using  var worker   new ProgressWorker lt TArgument gt   Action   action                         worker RunWorkerAsync                worker RunWorkerCompleted    worker RunWorkerCompleted                              ShowDialog                         void worker RunWorkerCompleted object sender  System ComponentModel RunWorkerCompletedEventArgs e                if  e Error    null                        Error   e Error              DialogResult   DialogResult Abort              return                     DialogResult   DialogResult OK            And how we use it   var dlg   new ProgressDlg lt string gt  obj   gt                                                                             DoWork                                        Thread Sleep 10000                                        MessageBox Show  Background task completed  obj                                          dlg RunWorker  SampleValue    if  dlg Error    null      MessageBox Show dlg Error Message   ERROR   MessageBoxButtons OK  MessageBoxIcon Error     dlg Dispose

User · Answer

It seems to me that you are operating on at least one false assumption   1  You don t need to raise the ProgressChanged event to have a responsive UI  In your question you say this      BackgroundWorker is not the answer   because it may be that I don t get the   progress notification  which means   there would be no call to   ProgressChanged as the DoWork is a   single call to an external function           Actually  it does not matter whether you call the ProgressChanged event or not  The whole purpose of that event is to temporarily transfer control back to the GUI thread to make an update that somehow reflects the progress of the work being done by the BackgroundWorker  If you are simply displaying a marquee progress bar  it would actually be pointless to raise the ProgressChanged event at all  The progress bar will continue rotating as long as it is displayed because the BackgroundWorker is doing its work on a separate thread from the GUI    On a side note  DoWork is an event  which means that it is not just  a single call to an external function   you can add as many handlers as you like  and each of those handlers can contain as many function calls as it likes    2  You don t need to call Application DoEvents to have a responsive UI  To me it sounds like you believe that the only way for the GUI to update is by calling Application DoEvents      I need to keep call the   Application DoEvents    for the   progress bar to keep rotating    This is not true in a multithreaded scenario  if you use a BackgroundWorker  the GUI will continue to be responsive  on its own thread  while the BackgroundWorker does whatever has been attached to its DoWork event  Below is a simple example of how this might work for you   private void ShowProgressFormWhileBackgroundWorkerRuns            this is your presumably long-running method     Action lt string  string gt  exec   DoSomethingLongAndNotReturnAnyNotification       ProgressForm p   new ProgressForm this        BackgroundWorker b   new BackgroundWorker            set the worker to call your long-running method     b DoWork     object sender  DoWorkEventArgs e    gt            exec Invoke path  parameters                  set the worker to close your progress form when it s completed     b RunWorkerCompleted     object sender  RunWorkerCompletedEventArgs e    gt            if  p    null  amp  amp  p Visible  p Close                   now actually show the form     p Show            this only tells your BackgroundWorker to START working         the current  i e   GUI  thread will immediately continue         which means your progress bar will update  the window        will continue firing button click events and all that        good stuff     b RunWorkerAsync        3  You can t run two methods at the same time on the same thread  You say this      I just need to call   Application DoEvents   so that the   Marque progress bar will work  while   the worker function works in the Main   thread         What you re asking for is simply not real  The  main  thread for a Windows Forms application is the GUI thread  which  if it s busy with your long-running method  is not providing visual updates  If you believe otherwise  I suspect you misunderstand what BeginInvoke does  it launches a delegate on a separate thread  In fact  the example code you have included in your question to call Application DoEvents between exec BeginInvoke and exec EndInvoke is redundant  you are actually calling Application DoEvents repeatedly from the GUI thread  which would be updating anyway   If you found otherwise  I suspect it s because you called exec EndInvoke right away  which blocked the current thread until the method finished    So yes  the answer you re looking for is to use a BackgroundWorker   You could use BeginInvoke  but instead of calling EndInvoke from the GUI thread  which will block it if the method isn t finished   pass an AsyncCallback parameter to your BeginInvoke call  instead of just passing null   and close the progress form in your callback  Be aware  however  that if you do that  you re going to have to invoke the method that closes the progress form from the GUI thread  since otherwise you ll be trying to close a form  which is a GUI function  from a non-GUI thread  But really  all the pitfalls of using BeginInvoke EndInvoke have already been dealt with for you with the BackgroundWorker class  even if you think it s   NET magic code   to me  it s just an intuitive and useful tool

User · Answer

Use the BackgroundWorker component it is designed for exactly this scenario     You can hook into its progress update events and update your progress bar   The BackgroundWorker class ensures the callbacks are marshalled to the UI thread so you don t need to worry about any of that detail either

User · Answer

If you want a  rotating  progress bar  why not set the progress bar style to  Marquee  and using a BackgroundWorker to keep the UI responsive  You won t achieve a rotating progress bar easier than using the  Marquee  - style

User · Answer

Reading your requirements the simplest way would be to display a mode-less form and use a standard System Windows Forms timer to update the progress on the mode-less form   No threads  no possible memory leaks   As this only uses the one UI thread  you would also need to call Application DoEvents   at certain points during your main processing to guarantee the progress bar is updated visually

User · Answer

BackgroundWorker is not the answer because it may be that I don t get the progress notification      What on earth does the fact that you re not getting progress notification have to do with the use of BackgroundWorker   If your long-running task doesn t have a reliable mechanism for reporting its progress  there s no way to reliably report its progress   The simplest possible way to report progress of a long-running method is to run the method on the UI thread and have it report progress by updating the progress bar and then calling Application DoEvents     This will  technically  work   But the UI will be unresponsive between calls to Application DoEvents     This is the quick and dirty solution  and as Steve McConnell observes  the problem with quick and dirty solutions is that the bitterness of the dirty remains long after the sweetness of the quick is forgotten   The next simplest way  as alluded to by another poster  is to implement a modal form that uses a BackgroundWorker to execute the long-running method   This provides a generally better user experience  and it frees you from having to solve the potentially complicated problem of what parts of your UI to leave functional while the long-running task is executing - while the modal form is open  none of the rest of your UI will respond to user actions   This is the quick and clean solution   But it s still pretty user-hostile   It still locks up the UI while the long-running task is executing  it just does it in a pretty way   To make a user-friendly solution  you need to execute the task on another thread   The easiest way to do that is with a BackgroundWorker   This approach opens the door to a lot of problems   It won t  leak   whatever that is supposed to mean   But whatever the long-running method is doing  it now has to do it in complete isolation from the pieces of the UI that remain enabled while it s running   And by complete  I mean complete   If the user can click anywhere with a mouse and cause some update to be made to some object that your long-running method ever looks at  you ll have problems   Any object that your long-running method uses which can raise an event is a potential road to misery   It s that  and not getting BackgroundWorker to work properly  that s going to be the source of all of the pain

User · Answer

Here is another sample code to use BackgroundWorker to update ProgressBar  just add BackgroundWorker and Progressbar to your main form and use below code   public partial class Form1   Form       public Form1               InitializeComponent          Shown    new EventHandler Form1 Shown           To report progress from the background worker we need to set this property     backgroundWorker1 WorkerReportsProgress   true         This event will be raised on the worker thread when the worker starts     backgroundWorker1 DoWork    new DoWorkEventHandler backgroundWorker1 DoWork          This event will be raised when we call ReportProgress     backgroundWorker1 ProgressChanged    new ProgressChangedEventHandler backgroundWorker1 ProgressChanged     void Form1 Shown object sender  EventArgs e           Start the background worker     backgroundWorker1 RunWorkerAsync         On worker thread so do our thing  void backgroundWorker1 DoWork object sender  DoWorkEventArgs e           Your background task goes here     for  int i   0  i  lt   100  i                     Report progress to  UI  thread         backgroundWorker1 ReportProgress i              Simulate long task         System Threading Thread Sleep 100              Back on the  UI  thread so we can update the progress bar void backgroundWorker1 ProgressChanged object sender  ProgressChangedEventArgs e           The progress percentage is a property of e     progressBar1 Value   e ProgressPercentage        refrence from codeproject

User · Answer

I have to throw the simplest answer out there  You could always just implement the progress bar and have no relationship to anything of actual progress  Just start filling the bar say 1  a second  or 10  a second whatever seems similar to your action and if it fills over to start again    This will atleast give the user the appearance of processing and make them understand to wait instead of just clicking a button and seeing nothing happen then clicking it more

[c#] Display progress bar while doing some work in C#?

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