The calling thread cannot access this object because a different thread owns it

Question

My code is as below      public CountryStandards         InitializeComponent        try               FillPageControls              catch  Exception ex                MessageBox Show ex Message   Country Standards   MessageBoxButton OK  MessageBoxImage Error                 lt summary gt      Fills the page controls       lt  summary gt  private void FillPageControls         popUpProgressBar IsOpen   true      lblProgress Content    Loading  Please wait          progress IsIndeterminate   true      worker   new BackgroundWorker        worker DoWork    new System ComponentModel DoWorkEventHandler worker DoWork       worker ProgressChanged    new System ComponentModel ProgressChangedEventHandler worker ProgressChanged       worker WorkerReportsProgress   true      worker WorkerSupportsCancellation   true      worker RunWorkerCompleted    new System ComponentModel RunWorkerCompletedEventHandler worker RunWorkerCompleted       worker RunWorkerAsync                           private void worker DoWork object sender  System ComponentModel DoWorkEventArgs e        GetGridData null  0      filling grid    private void worker ProgressChanged object sender  System ComponentModel ProgressChangedEventArgs e        progress Value   e ProgressPercentage     private void worker RunWorkerCompleted object sender  System ComponentModel RunWorkerCompletedEventArgs e        worker   null      popUpProgressBar IsOpen   false        filling Region dropdown     Standards UDMCountryStandards objUDMCountryStandards   new Standards UDMCountryStandards        objUDMCountryStandards Operation    SELECT REGION       DataSet dsRegionStandards   objStandardsBusinessLayer GetCountryStandards objUDMCountryStandards       if   StandardsDefault IsNullOrEmptyDataTable dsRegionStandards  0           StandardsDefault FillComboBox cmbRegion  dsRegionStandards Tables 0    Region    RegionId           filling Currency dropdown     objUDMCountryStandards   new Standards UDMCountryStandards        objUDMCountryStandards Operation    SELECT CURRENCY       DataSet dsCurrencyStandards   objStandardsBusinessLayer GetCountryStandards objUDMCountryStandards       if   StandardsDefault IsNullOrEmptyDataTable dsCurrencyStandards  0           StandardsDefault FillComboBox cmbCurrency  dsCurrencyStandards Tables 0    CurrencyName    CurrencyId         if  Users UserRole     Admin           btnSave IsEnabled   false           lt summary gt      Gets the grid data       lt  summary gt       lt param name  sender  gt The sender  lt  param gt       lt param name  pageIndex  gt Index of the page   used in case of paging     lt  pamam gt  private void GetGridData object sender  int pageIndex        Standards UDMCountryStandards objUDMCountryStandards   new Standards UDMCountryStandards        objUDMCountryStandards Operation    SELECT       objUDMCountryStandards Country   txtSearchCountry Text Trim      string Empty   txtSearchCountry Text   null      DataSet dsCountryStandards   objStandardsBusinessLayer GetCountryStandards objUDMCountryStandards       if   StandardsDefault IsNullOrEmptyDataTable dsCountryStandards  0   amp  amp   chkbxMarketsSearch IsChecked    true    chkbxBudgetsSearch IsChecked    true    chkbxProgramsSearch IsChecked    true                 DataTable objDataTable   StandardsDefault FilterDatatableForModules dsCountryStandards Tables 0    Country   chkbxMarketsSearch  chkbxBudgetsSearch  chkbxProgramsSearch           dgCountryList ItemsSource   objDataTable DefaultView            else               MessageBox Show  No Records Found    Country Standards   MessageBoxButton OK  MessageBoxImage Information           btnClear Click null  null             The step objUDMCountryStandards Country   txtSearchCountry Text Trim      string Empty   txtSearchCountry Text   null  in get grid data throws exception      The calling thread cannot access this object because a different   thread owns it    What s wrong here

User · Answer

For some reason Candide s answer didn t build  It was helpful  though  as it led me to find this  which worked perfectly   System Windows Threading Dispatcher CurrentDispatcher Invoke  Action       gt         your code here

User · Answer

The problem is that you are calling GetGridData from a background thread   This method accesses several WPF controls which are bound to the main thread   Any attempt to access them from a background thread will lead to this error     In order to get back to the correct thread you should use SynchronizationContext Current Post   However in this particular case it seems like the majority of the work you are doing is UI based   Hence you would be creating a background thread just to go immediately back to the UI thread and do some work   You need to refactor your code a bit so that it can do the expensive work on the background thread and then post the new data to the UI thread afterwards

User · Answer

There are definitely different ways to do this depending on your needs  One way I use a UI-updating thread  that s not the main UI thread  is to have the thread start a loop where the entire logical processing loop is invoked onto the UI thread  Example  public SomeFunction         bool working   true      Thread t   new Thread      gt                   Don t put the working bool in here  otherwise it will             belong to the new thread and not the main UI thread          while  working                        Application Current Dispatcher Invoke      gt                                   Put your entire logic code in here                     All of this code will process on the main UI thread because                     of the Invoke                     By doing it this way  you don t have to worry about Invoking individual                     elements as they are needed                                       With this  code executes entirely on main UI thread  This can be a pro for amateur programmers that have difficulty wrapping their heads around cross-threaded operations  However  it can easily become a con with more complex UIs  especially if performing animations   Really  this is only to fake a system of updating the UI and then returning to handle any events that have fired in lieu of efficient cross-threading operations

User · Answer

this happened with me because I tried to access UI component in another thread insted of UI thread   like this  private void button Click object sender  RoutedEventArgs e        new Thread SyncProcces  Start       private void SyncProcces         string val1   null  val2   null        here is the problem      val1   textBox1 Text   access UI in another thread     val2   textBox2 Text   access UI in another thread     localStore   new LocalStore val1       remoteStore   new RemoteStore val2       to solve this problem  wrap any ui call inside what Candide mentioned above in his answer  private void SyncProcces         string val1   null  val2   null      this Dispatcher Invoke  Action       gt         this refer to form in WPF application          val1   textBox Text          val2   textBox Copy Text               localStore   new LocalStore val1       remoteStore   new RemoteStore val2

User · Answer

You need to do it on the UI thread  Use  Dispatcher BeginInvoke new Action      gt   GetGridData null  0

User · Answer

As mentioned here  Dispatcher Invoke could freeze the UI  Should use Dispatcher BeginInvoke instead   Here is a handy extension class to simplify the checking and calling dispatcher invocation   Sample usage   call from WPF window   this Dispatcher InvokeIfRequired new Action      gt        logTextbox AppendText message       logTextbox ScrollToEnd           Extension class   using System  using System Windows Threading   namespace WpfUtility       public static class DispatcherExtension               public static void InvokeIfRequired this Dispatcher dispatcher  Action action                        if  dispatcher    null                                return                            if   dispatcher CheckAccess                                  dispatcher BeginInvoke action  DispatcherPriority ContextIdle                   return                            action

User · Answer

This works for me   new Thread      gt                     Thread CurrentThread IsBackground   false          Application Current Dispatcher BeginInvoke DispatcherPriority Background   SendOrPostCallback delegate                Your Code here              null              Start

User · Answer

Another good use for Dispatcher Invoke is for immediately updating the UI in a function that performs other tasks      Force WPF to render UI changes immediately with this magic line of code    Dispatcher Invoke new Action      gt        DispatcherPriority ContextIdle     I use this to update button text to  Processing     and disable it while making WebClient requests

User · Answer

To add my 2 cents  the exception can occur even if you call your code through System Windows Threading Dispatcher CurrentDispatcher Invoke     The point is that you have to call Invoke   of the Dispatcher of the control that you re trying to access  which in some cases may not be the same as System Windows Threading Dispatcher CurrentDispatcher  So instead you should use YourControl Dispatcher Invoke   to be safe  I was banging my head for a couple of hours before I realized this    Update  For future readers  it looks like this has changed in the newer versions of  NET  4 0 and above   Now you no longer have to worry about the correct dispatcher when updating UI-backing properties in your VM  WPF engine will marshal cross-thread calls on the correct UI thread  See more details here  Thanks to  aaronburro for the info and link  You may also want to read our conversation below in comments

User · Answer

Also  another solution is ensuring your controls are created in UI thread  not by a background worker thread for example

User · Answer

I kept getting the error when I added cascading comboboxes to my WPF application  and resolved the error by using this API       using System Windows Data       private readonly object  lock   new object        private CustomObservableCollection lt string gt   myUiBoundProperty      public CustomObservableCollection lt string gt  MyUiBoundProperty               get   return  myUiBoundProperty            set                       if  value     myUiBoundProperty  return               myUiBoundProperty   value              NotifyPropertyChanged nameof MyUiBoundProperty                         public MyViewModelCtor INavigationService navigationService                   Other code           BindingOperations EnableCollectionSynchronization AvailableDefectSubCategories   lock             For details  please see https   msdn microsoft com query dev14 query appId Dev14IDEF1 amp l EN-US amp k k System Windows Data BindingOperations EnableCollectionSynchronization  k TargetFrameworkMoniker- NETFramework Version 3Dv4 7  k DevLang-csharp  amp rd true

User · Answer

If you encounter this problem and UI Controls were created on a separate worker thread when working with BitmapSource or ImageSource in WPF  call Freeze   method first before passing the BitmapSource or ImageSource as a parameter to any method  Using Application Current Dispatcher Invoke   does not work in such instances

User · Answer

I also found that System Windows Threading Dispatcher CurrentDispatcher Invoke   is not always dispatcher of target control  just as dotNet wrote in his answer  I didn t had access to control s own dispatcher  so I used Application Current Dispatcher and it solved the problem

User · Answer

This is a common problem with people getting started  Whenever you update your UI elements from a thread other than the main thread  you need to use   this Dispatcher Invoke      gt              your code here        You can also use control Dispatcher CheckAccess   to check whether the current thread owns the control  If it does own it  your code looks as normal  Otherwise  use above pattern

[c#] The calling thread cannot access this object because a different thread owns it

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