Accessing UI Main Thread safely in WPF

Question

I have an application which updates my datagrid each time a log file that I m watching gets updated  Appended with new text  in the following manner   private void DGAddRow string name  FunctionType ft                        ASCIIEncoding ascii   new ASCIIEncoding         CommDGDataSource ds   new CommDGDataSource         int position   0      string   data split   ft Data Split           foreach  AttributeType at in ft Types                if  at IsAddress                         ds Source   HexString2Ascii data split position                ds Destination   HexString2Ascii data split position 1                break                    else                       position    at Size                      ds Protocol   name      ds Number   rowCount      ds Data   ft Data      ds Time   ft Time       dataGridRows Add ds         rowCount                      private void FileSystemWatcher                 FileSystemWatcher watcher   new FileSystemWatcher Environment CurrentDirectory           watcher Filter   syslogPath          watcher NotifyFilter   NotifyFilters LastAccess   NotifyFilters LastWrite               NotifyFilters FileName   NotifyFilters DirectoryName          watcher Changed    new FileSystemEventHandler watcher Changed           watcher EnableRaisingEvents   true             private void watcher Changed object sender  FileSystemEventArgs e                if  File Exists syslogPath                         string line   GetLine syslogPath currentLine               foreach  CommRuleParser crp in crpList                                FunctionType ft   new FunctionType                    if  crp ParseLine line  out ft                                         DGAddRow crp Protocol  ft                                               currentLine                      else             MessageBox Show UIConstant COMM SYSLOG NON EXIST WARNING           When the event is raised for the FileWatcher  because it creates a separate thread  when I try to run dataGridRows Add ds   to add the new row  the program just crashes without any warning given during debug mode   In Winforms  this was easily solved by utilizing the Invoke function but I am not sure how to go about this in WPF

User · Answer

Use  Dispatcher Invoke DispatcherPriority  Delegate   to change the UI from another thread or from background   Step 1  Use the following namespaces  using System Windows  using System Threading  using System Windows Threading    Step 2  Put the following line where you need to update UI  Application Current Dispatcher Invoke DispatcherPriority Background  new ThreadStart delegate         Update UI here           Syntax   BrowsableAttribute false   public object Invoke    DispatcherPriority priority    Delegate method         Parameters      priority      Type  System Windows Threading DispatcherPriority      The priority  relative to the other pending operations in the   Dispatcher event queue  the specified method is invoked       method      Type  System Delegate      A delegate to a method that takes no arguments  which is pushed onto   the Dispatcher event queue       Return Value      Type  System Object      The return value from the delegate being invoked or null if the   delegate has no return value       Version Information      Available since  NET Framework 3 0

User · Answer

The best way to go about it would be to get a SynchronizationContext from the UI thread and use it  This class abstracts marshalling calls to other threads  and makes testing easier  in contrast to using WPF s Dispatcher directly   For example   class MyViewModel       private readonly SynchronizationContext  syncContext       public MyViewModel                    we assume this ctor is called from the UI thread           syncContext   SynchronizationContext Current                         private void watcher Changed object sender  FileSystemEventArgs e                  syncContext Post o   gt  DGAddRow crp Protocol  ft   null

User · Answer

You can use   Dispatcher Invoke Delegate  object     on the Application s  or any UIElement s  dispatcher   You can use it for example like this     Application Current Dispatcher Invoke new Action      gt       Your code here           or   someControl Dispatcher Invoke new Action      gt       Your code here

[c#] Accessing UI (Main) Thread safely in WPF

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