Force GUI update from UI Thread

Question

In WinForms  how do I force an immediate UI update from UI thread    What I m doing is roughly   label Text    Please Wait     try        SomewhatLongRunningOperation       catch Exception e        label Text    Error      e Message      return    label Text    Success      Label text does not get set to  Please Wait     before the operation   I solved this using another thread for the operation  but it gets hairy and I d like to simplify the code

User · Answer

Try calling label Invalidate    http   msdn microsoft com en-us library system windows forms control invalidate VS 80  aspx

User · Answer

At first I wondered why the OP hadn t already marked one of the responses as the answer  but after trying it myself and still have it not work  I dug a little deeper and found there s much more to this issue then I d first supposed    A better understanding can be gained by reading from a similar question  Why won  39 t control update refresh mid-process  Lastly  for the record  I was able to get my label to update by doing the following   private void SetStatus string status         lblStatus Text   status      lblStatus Invalidate        lblStatus Update        lblStatus Refresh        Application DoEvents        Though from what I understand this is far from an elegant and correct approach to doing it  It s a hack that may or may not work depending upon how busy the thread is

User · Answer

Call label Invalidate and then label Update   - usually the update only happens after you exit the current function but calling Update forces it to update at that specific place in code  From MSDN      The Invalidate method governs what gets painted or repainted  The Update method governs when the painting or repainting occurs  If you use the Invalidate and Update methods together rather than calling Refresh  what gets repainted depends on which overload of Invalidate you use  The Update method just forces the control to be painted immediately  but the Invalidate method governs what gets painted when you call the Update method

User · Answer

If you only need to update a couple controls   update   is sufficient   btnMyButton BackColor Color Green     it eventually turned green  after a delay btnMyButton Update       after I added this  it turned green quickly

User · Answer

Think I have the answer  distilled from the above and a little experimentation   progressBar Value   progressBar Maximum - 1  progressBar Maximum   progressBar Value    I tried decrementing the value and the screen updated even in debug mode  but that would not work for setting progressBar Value to progressBar Maximum  because you cannot set the progress bar value above the maximum  so I first set the progressBar Value to progressBar Maximum -1  then set progressBar Maxiumum to equal progressBar Value  They say there is more than one way of killing a cat  Sometimes I d like to kill Bill Gates or whoever it is now  o    With this result  I did not even appear to need to Invalidate    Refresh    Update    or do anything to the progress bar or its Panel container or the parent Form

User · Answer

I had the same problem with property Enabled and I discovered a first chance exception raised because of it is not thread-safe  I found solution about  How to update the GUI from another thread in C    here https   stackoverflow com a 661706 1529139 And it works

User · Answer

I ve just stumbled over the same problem and found some interesting information and I wanted to put in my two cents and add it here     First of all  as others have already mentioned  long-running operations should be done by a thread  which can be a background worker  an explicit thread  a thread from the threadpool or  since  Net 4 0  a task  Stackoverflow 570537  update-label-while-processing-in-windows-forms  so that the UI keeps responsive     But for short tasks there is no real need for threading although it doesn t hurt of course     I have created a winform with one button and one label to analyze this problem   System  Void button1 Click System  Object   sender  System  EventArgs   e      label1- gt Text    Start 1     label1- gt Update      System  Threading  Thread  Sleep 5000      do other work     My analysis was stepping over the code  using F10  and seeing what happened  And after reading this article Multithreading in WinForms I have found something interesting  The article says at the bottom of the first page  that the UI thread can not repaint the UI until the currently executed function finishes and the window is marked by Windows as  not responding  instead after a while  I have also noticed that on my test application from above while stepping through it  but only in certain cases      For the following test it is important to not have Visual Studio set to fullscreen  you must be able to see your little application window at the same time next to it  You must not have to switch between the Visual Studio window for debugging and your application window to see what happens  Start the application  set a breakpoint at label1- gt Text      put the application window beside the VS window and place the mouse cursor over the VS window       When I click once on VS after app start  to put the focues there and enable stepping  and step through it WITHOUT moving the mouse  the new text is set and the label is updated in the update   function  This means  the UI is repainted obviously  When I step over the first line  then move the mouse around a lot and click somewhere  then step further  the new text is likely set and the update   function is called  but the UI is not updated repainted and the old text remains there until the button1 click   function finishes  Instead of repainting  the window is marked as  not responsive   It also doesn t help to add this- gt Update    to update the whole form    Adding Application  DoEvents    gives the UI a chance to update repaint  Anyway you have to take care that the user can not press buttons or perform other operations on the UI that are not permitted   Therefore  Try to avoid DoEvents     better use threading  which I think is quite simple in  Net   But   Jagd  Apr 2  10 at 19 25  you can omit  refresh   and  invalidate      My explanations is as following  AFAIK winform still uses the WINAPI function  Also MSDN article about System Windows Forms Control Update method refers to WINAPI function WM PAINT  The MSDN article about WM PAINT states in its first sentence that the WM PAINT command is only sent by the system when the message queue is empty  But as the message queue is already filled in the 2nd case  it is not send and thus the label and the application form are not repainted    lt  joke  Conclusion  so you just have to keep the user from using the mouse  -   lt   joke

User · Answer

After updating the UI  start a task to perform with the long running operation   label Text    Please Wait       Task lt string gt  task   Task lt string gt  Factory StartNew      gt        try               SomewhatLongRunningOperation            return  Success              catch  Exception e                return  Error      e Message            Task UITask   task ContinueWith  ret    gt        label Text   ret Result     TaskScheduler FromCurrentSynchronizationContext       This works in  NET 3 5 and later

User · Answer

It s very tempting to want to  fix  this and force a UI update  but the best fix is to do this on a background thread and not tie up the UI thread  so that it can still respond to events

User · Answer

Call Application DoEvents   after setting the label  but you should do all the work in a separate thread instead  so the user may close the window

User · Answer

you can try this  using System Windows Forms     u need this to include   MethodInvoker updateIt   delegate                                       this label1 Text    Started                         this label1 BeginInvoke updateIt     See if it works

[c#] Force GUI update from UI Thread

Examples related to c#

Examples related to winforms

Examples related to multithreading