Updating GUI WPF using a different thread

Question

Just have a problem here that I have no idea how to fix  I am doing a small project which involves a GUI and serial data  The GUI is being run by the main thread and since the data variables that hold my incoming serial data need to be updated continuously  these are being updated in a second thread  The problem is when I need to update some textboxes on the GUI  these need to be updated with data from the secondary thread and that is where my problem lies  I can t update them directly from the secondary thread and I have no idea how I would transfer data from my secondary thread and work out a system of updating them from main thread  I have put my code below   Any help would be great   using System  using System Collections Generic  using System Linq  using System Text  using System Windows  using System Windows Controls  using System Windows Data  using System Windows Documents  using System Windows Input  using System Windows Media  using System Windows Media Imaging  using System Windows Navigation  using System Windows Shapes  using System IO  using System IO Ports  using System Threading   namespace GUIBike            lt summary gt          Interaction logic for MainWindow xaml          lt  summary gt      public partial class MainWindow   Window               public static string inputdata          public static int MaximumSpeed  maximumRiderInput  RiderInput  Time  CurrentSpeed  DistanceTravelled  MaximumMotorOutput  MotorOutput  InputSpeed          public static string SaveDataString          public Thread Serial          public static SerialPort SerialData          public static string   portlist   SerialPort GetPortNames            public static string   SaveData   new string 4           public static string directory    C               public MainWindow                         Serial   new Thread ReadData               InitializeComponent                int Count   0              for  Count   0  Count  lt  portlist Length  Count                                  ComPortCombo Items Add portlist Count                                     private void StartDataButton Click object sender  RoutedEventArgs e                        SerialData   new SerialPort ComPortCombo Text  19200  Parity None  8  StopBits One               SerialData Open                SerialData WriteLine  P                Serial Start                StartDataButton IsEnabled   false              EndDataButton IsEnabled   true              ComPortCombo IsEnabled   false              CurrentSpeed   0              MaximumSpeed   0              Time   0              DistanceTravelled   0              MotorOutput   0              RiderInput   0              SaveData 0                    SaveData 1                    SaveData 2                    SaveData 3                    SaveDataButton IsEnabled   false              if  SerialData IsOpen                                ComPortStatusLabel Content    OPEN                   SerialData NewLine     n                   SerialData WriteLine  0                    SerialData WriteLine   n                                     private void EndDataButton Click object sender  RoutedEventArgs e                        SerialData Close                SaveDataButton IsEnabled   true              SerialData WriteLine  1                SerialData WriteLine  0                if   SerialData IsOpen                                ComPortStatusLabel Content    CLOSED                             int i   0              for  i   0  i  lt  4  i                                  if  i    0                                        SaveDataString    MaximumSpeed during the Ride was       Convert ToString MaximumSpeed     m h                       SaveData i    SaveDataString                                    if  i    1                                        SaveDataString    Total Distance Travelled       Convert ToString DistanceTravelled     m                       SaveData i    SaveDataString                                    if  i    2                                        SaveDataString    Maximum Rider Input Power       Convert ToString maximumRiderInput     Watts                       SaveData i    SaveDataString                                    if  i    3                                        SaveDataString    Maximum Motor Output Power       Convert ToString MaximumMotorOutput     Watts                       SaveData i    SaveDataString                                                     private void SaveDataButton Click object sender  RoutedEventArgs e                          File WriteAllBytes directory    image    imageNO     txt        saves the file to Disk                 File WriteAllLines directory    BikeData txt   SaveData                      public void ReadData                         int counter   0               while  SerialData IsOpen                                if  counter    0                                          try                                                 InputSpeed   Convert ToInt16 SerialData ReadChar                             CurrentSpeed   InputSpeed                          if  CurrentSpeed  gt  MaximumSpeed                                                        MaximumSpeed   CurrentSpeed                                                    SpeedTextBox Text    Current Wheel Speed       Convert ToString CurrentSpeed     Km h                           DistanceTravelled   DistanceTravelled    Convert ToInt16 CurrentSpeed    Time                           DistanceTravelledTextBox Text    Total Distance Travelled       Convert ToString DistanceTravelled     Km                                                 catch  Exception                                        if  counter    1                                        try                                               RiderInput   Convert ToInt16 SerialData ReadLine                             if  RiderInput  gt  maximumRiderInput                                                        maximumRiderInput   RiderInput                                                    RiderInputTextBox Text    Current Rider Input Power      Convert ToString RiderInput     Watts                                             catch  Exception                                        if  counter    2                                        try                                               MotorOutput   Convert ToInt16 SerialData ReadLine                             if  MotorOutput  gt  MaximumMotorOutput                                                        MaximumMotorOutput   MotorOutput                                                     MotorOutputTextBox Text    Current Motor Output       Convert ToString MotorOutput     Watts                                             catch  Exception                                        counter                    if  counter    3                                        counter   0                                                     private void ComPortCombo SelectionChanged object sender  SelectionChangedEventArgs e                        StartDataButton IsEnabled   true                      private void Window Closed object sender  RoutedEventArgs e                        if  SerialData IsOpen                                SerialData Close

User · Answer

As akjoshi and Julio say this is about dispatching an Action to update the GUI on the same thread as the GUI item but from the method that is handling the background data. You can see this code in specific form in akjoshi's answer above. This is a general version.

myTextBlock.Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Normal,
                                   new Action(delegate() 
                                      {
                                      myTextBlock.Text = Convert.ToString(myDataObject.getMeData());
                                      }));

The critical part is to call the dispatcher of your UI object - that ensures you have the correct thread.

From personal experience it seems much easier to create and use the Action inline like this. Declaring it at class level gave me lots of problems with static/non-static contexts.

User · Answer

Here is a full example that updates UI textboxes   lt Window x Class  WpfThreading MainWindow      xmlns  http   schemas microsoft com winfx 2006 xaml presentation      xmlns x  http   schemas microsoft com winfx 2006 xaml      xmlns d  http   schemas microsoft com expression blend 2008      xmlns mc  http   schemas openxmlformats org markup-compatibility 2006      xmlns local  clr-namespace WpfThreading      mc Ignorable  d      Title  MainWindow  Height  450  Width  216 84  gt   lt Grid Margin  0 0 2 0  gt       lt Button Content  Button  HorizontalAlignment  Left  Margin  10 10 0 0              VerticalAlignment  Top  Width  75  Click  Button Click   gt       lt TextBox HorizontalAlignment  Left  Margin  10 35 0 10  TextWrapping  Wrap  Name  mtextBox  Width  87    VerticalScrollBarVisibility  Auto   gt       lt TextBox HorizontalAlignment  Left  Margin  111 35 0 10  TextWrapping  Wrap  x Name  mtextBox2  Width  87    VerticalScrollBarVisibility  Auto   gt   lt  Grid gt  lt  Window gt    and in the code   public partial class MainWindow   Window       public MainWindow                 InitializeComponent               private void Button Click object sender  RoutedEventArgs e                new Thread DoSomething  Start            new Thread DoSomething2  Start                public void DoSomething                 for  int i   0  i  lt  100  i                          Dispatcher BeginInvoke new Action      gt                    mtextBox Text       i ToString    Environment NewLine                    DispatcherPriority SystemIdle                Thread Sleep 100                         public void DoSomething2                 for  int i   100  i  gt  0  i--                        Dispatcher BeginInvoke new Action      gt                    mtextBox2 Text       i ToString    Environment NewLine                    DispatcherPriority SystemIdle                Thread Sleep 100

User · Answer

You may use a delegate to solve this issue  Here is an example that is showing how to update a textBox using diffrent thread   public delegate void UpdateTextCallback string message    private void TestThread         for  int i   0  i  lt   1000000000  i                  Thread Sleep 1000                           richTextBox1 Dispatcher Invoke              new UpdateTextCallback this UpdateText               new object     i ToString                        private void UpdateText string message        richTextBox1 AppendText message     n       private void button1 Click object sender  RoutedEventArgs e       Thread test   new Thread new ThreadStart TestThread       test Start        TestThread method is used by thread named test to update textBox

User · Answer

there   I am also developing a serial port testing tool using WPF   and I d like to share some experience of mine   I think you should refactor your source code according to MVVM design pattern   At the beginning  I met the same problem as you met  and I solved it using this code   new Thread      gt         while                     SomeTextBox Dispatcher BeginInvoke  Action       gt  SomeTextBox Text                   Start      This works  but is too ugly  I have no idea how to refactor it  until I saw this  http   www codeproject com Articles 165368 WPF-MVVM-Quick-Start-Tutorial  This is a very kindly step-by-step MVVM tutorial for beginners  No shiny UI  no complex logic  only the basic of MVVM

User · Answer

You need to use Dispatcher BeginInvoke  I did not test it but you can check this link this is the same link provided by Julio G  to have better understanding on how to update the UI controls from different thread  I have modified your ReadData   code   public void ReadData         int counter   0       while  SerialData IsOpen                if  counter    0                          try                                 InputSpeed   Convert ToInt16 SerialData ReadChar                     CurrentSpeed   InputSpeed                  if  CurrentSpeed  gt  MaximumSpeed                                        MaximumSpeed   CurrentSpeed                        SpeedTextBox Dispatcher BeginInvoke System Windows Threading DispatcherPriority Normal          new Action delegate     SpeedTextBox Text    Current Wheel Speed       Convert ToString CurrentSpeed     Km h        update GUI from this thread                   DistanceTravelled   DistanceTravelled    Convert ToInt16 CurrentSpeed    Time        DistanceTravelledTextBox Dispatcher BeginInvoke System Windows Threading DispatcherPriority Normal          new Action delegate    DistanceTravelledTextBox Text    Total Distance Travelled       Convert ToString DistanceTravelled     Km        update GUI from this thread                                catch  Exception                        if  counter    1                        try                               RiderInput   Convert ToInt16 SerialData ReadLine                     if  RiderInput  gt  maximumRiderInput                                        maximumRiderInput   RiderInput                                               RiderInputTextBox Dispatcher BeginInvoke System Windows Threading DispatcherPriority Normal           new Action delegate     RiderInputTextBox Text    Current Rider Input Power      Convert ToString RiderInput     Watts        update GUI from this thread                           catch  Exception                        if  counter    2                        try                               MotorOutput   Convert ToInt16 SerialData ReadLine                     if  MotorOutput  gt  MaximumMotorOutput                                        MaximumMotorOutput   MotorOutput                        MotorOutputTextBox Dispatcher BeginInvoke System Windows Threading DispatcherPriority Normal           new Action delegate     MotorOutputTextBox Text    Current Motor Output       Convert ToString MotorOutput     Watts        update GUI from this thread                                                   catch  Exception                        counter            if  counter    3                        counter   0

User · Answer

Use Following Method to Update GUI        Public Void UpdateUI                     Here update your label  button or any string related object              Dispatcher CurrentDispatcher Invoke DispatcherPriority Background  new ThreadStart delegate                     Application Current Dispatcher Invoke DispatcherPriority Background  new ThreadStart delegate                 Keep it in Mind when you use this method at that time do not Update same object direct from dispatcher thread otherwise you get only that updated string and this method is helpless useless  If still not working then Comment that line inside method and un-comment commented one both have nearly same effect just different way to access it

User · Answer

You have a couple of options here  I think   One would be to use a BackgroundWorker  This is a common helper for multithreading in applications  It exposes a DoWork event which is handled on a background thread from the Thread Pool and a RunWorkerCompleted event which is invoked back on the main thread when the background thread completes  It also has the benefit of try catching the code running on the background thread so that an unhandled exception doesn t kill the application   If you don t want to go that route  you can use the WPF dispatcher object to invoke an action to update the GUI back onto the main thread  Random reference   http   www switchonthecode com tutorials working-with-the-wpf-dispatcher  There are many other options around too  but these are the two most common that come to mind

User · Answer

You can use Dispatcher Invoke to update your GUI from a secondary thread   Here is an example               private void Window Loaded object sender  RoutedEventArgs e                new Thread DoSomething  Start              public void DoSomething                 for  int i   0  i  lt  100000000  i                             this Dispatcher Invoke     gt                  textbox Text i ToString

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