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C#/WPF - I can't update UI from a backgroundworker

I have a code that fetches tweets from a specific Twitter account using Tweetsharp library, creates instance of a custom UserControl and post tweet text to that UserControl then add it to a StackPanel.
However, I have to get a lot of tweets and it seems that the application would freeze while adding user controls to the StackPanel. I tried using BackgroundWorker, but I wasn't lucky until now.
My code :
private readonly BackgroundWorker worker = new BackgroundWorker();
// This ( UserControl ) is used in the MainWindow.xaml
private void UserControl_Loaded_1(object sender, RoutedEventArgs e)
{
worker.DoWork += worker_DoWork;
worker.RunWorkerCompleted += worker_RunWorkerCompleted;
worker.RunWorkerAsync();
}
private void worker_DoWork(object sender, DoWorkEventArgs e)
{
int usrID;
var service = new TwitterService(ConsumerKey, ConsumerSecret);
service.AuthenticateWith(AccessToken, AccessTokenSecret);
ListTweetsOnUserTimelineOptions options = new ListTweetsOnUserTimelineOptions();
options.UserId = usrID;
options.IncludeRts = true;
options.Count = 10;
twitterStatuses = service.ListTweetsOnUserTimeline(options);
}
private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
try
{
foreach (var item in twitterStatuses)
{
TweetViewer tweetViewer = new TweetViewer(); // A UserControl within another UserControl
tweetViewer.Tweet = item.Text;
tweetViewer.Username = "#stackoverflow";
tweetViewer.RealName = "Stack Overflow"
tweetViewer.Avatar = ImageSourcer(item.Author.ProfileImageUrl);
stackPanel.Children.Add(tweetViewer);
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
What I want to do now is to solve the problem of not being able to perform the code contained in worker_RunWorkerCompleted within a BackgroundWorker but every time I try to perform it using a BackgroundWorker it fails & gives me errors like :
The calling thread must be STA, because many UI components require this.
I tried also using a STA System.Threading.Thread instead of the BackgroundWorker but without luck!
What am I missing ? I'm really new to WPF and I may be ignoring something important.

You get this exception because your background worker uses a new thread, and this thread is different than the main UI thread.
To simplify the error message says that you cannot change your UI element from another thread, they are independant.
This answer will solve your problem.
I also found this answer from #Marc Gravell
///...blah blah updating files
string newText = "abc"; // running on worker thread
this.Invoke((MethodInvoker)delegate {
someLabel.Text = newText; // runs on UI thread
});
///...blah blah more updating files

How to update the UI in real-time using Threads

I am developing an application which will actively read from a file and analyze and display information in that file to the UI in real time.
Everything I have read tells me I should use some kind of threading to do this. I have explored background workers and also tried creating a separate thread at run time and using that thread to update all of the UI elements.
The problem comes in when I can't (or shouldn't) be making cross thread calls, as the original UI elements were created on a different thread.
Is there a way to create these UI elements on the thread that will be updating them? What is the best way to do this?
edit: There was a reply to this post (which is now gone) explaining how I should do this. After updating my code with the method described
This is the updated code I have used. Everything is fine until I add in the file system watcher. As soon as I add that I get the same error about not making cross thread calls.
Session is a class I created that parses through the log file
private Session s1 = new Session("");
private FileSystemWatcher fsw;
private OpenFileDialog ofd1 = new OpenFileDialog();
private BackgroundWorker bgw;
private bool logActive = false;
public frmMain()
{
InitializeComponent();
bgw = new BackgroundWorker();
bgw.WorkerReportsProgress = true;
bgw.ProgressChanged += HandleProgressChanged;
bgw.DoWork += HandleDoWork;
fsw = new FileSystemWatcher(#"H:\Logs", "*.txt");
fsw.SynchronizingObject = this;
fsw.IncludeSubdirectories = false;
fsw.EnableRaisingEvents = true;
fsw.NotifyFilter = NotifyFilters.Size;
fsw.Changed += new FileSystemEventHandler(fsw_OnChanged);
}
private void frmMain_Load(object sender, EventArgs e)
{
ofd1.Filter = "log files (*.txt)|*.txt|All files (*.*)|*.*";
ofd1.FilterIndex = 2;
ofd1.RestoreDirectory = true;
}
private void fsw_OnChanged(object source, System.IO.FileSystemEventArgs e)
{
bgw.RunWorkerAsync();
}
// this runs on the UI thread
// here's where you update the UI based on the information from the event args
private void HandleProgressChanged(object sender, ProgressChangedEventArgs e)
{
for (int i = s1.previousLineNumber; i < s1.GetMessageCount(); i++)
{
ListViewItem lvi = new ListViewItem((s1.GetMessage(i).date).ToString());
lvi.SubItems.Add(s1.GetMessage(i).type.ToString());
lvi.SubItems.Add(s1.GetMessage(i).data);
listView1.Items.Add(lvi);
}
}
// this runs on a background thread; you cannot modify UI controls here
private void HandleDoWork(object sender, DoWorkEventArgs e)
{
s1.ParseLiveFile();
bgw.ReportProgress(100);
}

In order to update the UI you should use Invoke or BeginInvoke.
void LengthyProcessInThread()
{
...
foreach(var item in file)
{
Invoke(delegate() {
.. Update UI here.
});
}
}
Invoke is a method on a control, Eg. the form containing the UI.
I wish you good luck with your quest.

How Run Two Operations concurrently in C#

I have a problem in my WPF app. I have a custom CircularProgressBar. When I retrieve data from database it takes a few seconds.
I would like to show the CircularProgressBar in my app while the data is retrieved.
This code runs the CircularProgressBar :
CircularProgressBar cb = new CircularProgressBar();
stk.Children.Add(cb);
ThreadStart thStart = delegate()
{
ThreadStart inv = delegate()
{
stk.Children.Remove(cb);
};
this.Dispatcher.Invoke(inv, null);
};
Thread myThread = new Thread(thStart);
myThread.Start();
in my custom class (Printer).
And where I call this window:
Printer p = new Printer();
p.Show();
//Code For retrieve Data from DataBase
p.close();
So this happens : CircularProgressBar shows for a few seconds and it not running. Where is my bug?

You can simply use background worker:
private BackgroundWorker bw = new BackgroundWorker();
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
private void bw_DoWork(object sender, DoWorkEventArgs e)
{
//load data from database
System.Threading.Thread.Sleep(1);
worker.ReportProgress(progressbar_value);
}
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
Progress.value= progressbar_value;
}
private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
//progress completed
}

This is not how you do stuff in wpf -
use a model to populate the data from the db and than bind CircularProgressBar visibility to
the state you're in (hide it when you completed the task).
all this boilerplate code should be in xaml.

If I were you, I would simplify life by using databinding with dependencyproperties.
What are the steps to follow.
1) Create a dependency property called IsBusyProperty of type bool in your custom progressbar.
2) Register a delegate to its value change event (this is done when you create the dependency property).
3) You can now bind this IsBusyProperty to a status in your code that says hey I am busy.
4) When the value is set to true you get your progressbar to start its magic.
5) When it is set to false you stop the magic.

It is far simpler to create a control with a storyboard that rotates, so long as your ui is not locked it will rotate then simply kill it afterward.
Try this

The calling thread cannot access this object (rewrited but same error)

I have a MainFrame window with imageViewer control on it. Also there is my dll which calculates changes for the image all was working fine before I decided to add ProgressDialog.(( The Idea was - firstly I am loading the image via dll to main frame (this still OK). Then if user clicks button then show ProgressDialog and in worker.DoWork create new image via the same dllwrapper class (I am using "new")
All seems to be ok but when i am trying to set my currentImage property of imageviewer control (this is nothing more then setter for Image)it show me this error!
This is the code of my userButtonClickHandler from where I am launching ProgressDialog:
void OnThumbnailClick(object sender, RoutedEventArgs e)
{
pd = new ProgressDlg();
pd.Cancel += CancelProcess;
int max = 1000;
System.Windows.Threading.Dispatcher pdDispatcher = pd.Dispatcher;
worker = new BackgroundWorker();
worker.WorkerSupportsCancellation = true;
LibWrap lwrap = new LibWrap();//!NEW instance for dll wrapper!
worker.DoWork += delegate(object s, DoWorkEventArgs args)
{
imageViewer.CurrentImage = lwrap.engine2(BitmapFrame.Create(MyPrj.App.draggedImage));//ERROR IS HERE!!!//The calling thread cannot access this object because a different thread owns it.
//what process??
};
worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args)
{
pd.Close();
};
worker.RunWorkerAsync();
pd.ShowDialog();
}
There is function from the same MainFrame class for canceling (There is OK too)
void CancelProcess(object sender, EventArgs e)
{
worker.CancelAsync();
}
This is class for ProgressDlg (it has nothing more then progress bar and cancel button):
public partial class ProgressDlg : Window
{
public ProgressDlg()
{
InitializeComponent();
}
public string ProgressText
{
set
{
this.lblProgress.Content = value;
}
}
public int ProgressValue
{
set
{
this.progress.Value = value;
}
}
public event EventHandler Cancel = delegate { };
private void btnCancel_Click(object sender, RoutedEventArgs e)
{
Cancel(sender, e);
}
}
}
I am working with this problem for (almost) two days and still couldn't find the solution. Help me please if you have an idea.
1 UPDATE
It seems to me that you was right about this threads - when I am trying to load previously loaded(initial) image (from the main thread) -it loads OK but if I am trying libWrap it fails due to processes conflict!
worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args)
{
imageViewer.Width = 1000;//work!
imageViewer.CurrentImage = MyPrj.App.draggedImage;//Work!
imageViewer.CurrentImage = lwrap.engine2(BitmapFrame.Create(MyPrj.App.draggedImage));//Fail =(!
}
2 UPDATE
I have tried this construction OnThumbnailClick
Application.Current.MainWindow.Dispatcher.BeginInvoke(new Action(() =>
{
imaeViewer.CurrentImage = lwrap.engine2(BitmapFrame.Create(FXPhotoStudio.App.draggedImage));
}
This caused same error/ Perhaps it will be correct to pass this value in MainThread (UI)? But I have no idea how.( I couldnot use serializers - becouse it is rapidly calling operation and this images are temporary/

WPF cannot alter items that were created on another thread.
So if you create an ImageViewer on one thread, you cannot alter it's properties on another thread.
Instead, use the Dispatcher, which is WPF's internal message queue for the main UI thread, to update your objects.
Or, use Henk's Answer to do your work on another thread, but return the result to the main thread so it can update your ImageViewer's properties

You need at least these changes:
worker.DoWork += delegate(object s, DoWorkEventArgs args)
{
args.Result = lwrap.engine2(BitmapFrame.Create(MyPrj.App.draggedImage));
};
worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args)
{
if (args.Error != null)
{ ... } // handle error
else if (args.Cancelled)
{ ... } // handle Cancel
else
{
imageViewer.CurrentImage = args.Result;
}
pd.Close();
}
I'm not sure if it's enough but try again.

The imageViewer was created on the main thread of the application (which is appropriate because it is a UI control). UI controls can ONLY be accessed by the thread which created it, and that thread must have its own dispatcher (by which I mean message loop).
Remove the threading code, and it will work.
If you want this to popup the window and then show the image when the conversion completes, you will have to store the returned image in a variable until you return to the main thread, and then make the assignment to the imageViewer.

How to change label content with timers throwing InvalidOperationException

I'm making an application and I'm using a timer in that application to change label content in WPF C# .NET.
In the timer's elapsed event I'm writing the following code
lblTimer.Content = "hello";
but its throwing an InvalidOperationException and gives a message The calling thread cannot access this object because a different thread owns it.
I'm using .NET framework 3.5 and WPF with C#.
Please help me.
Thanks in advance.

For .NET 4.0 it is much simpler to use a DispatcherTimer. The eventhandler is then in the UI thread and it can set properties of the control directly.
private DispatcherTimer updateTimer;
private void initTimer
{
updateTimer = new DispatcherTimer(DispatcherPriority.SystemIdle);
updateTimer.Tick += new EventHandler(OnUpdateTimerTick);
updateTimer.Interval = TimeSpan.FromMilliseconds(1000);
updateTimer.Start();
}
private void OnUpdateTimerTick(object sender, EventArgs e)
{
lblTimer.Content = "hello";
}

InvokeRequired doesn't work in wpf.
The proper way the update a GUI element owned by another thread is this :
Declare this on module level :
delegate void updateLabelCallback(string tekst);
This is the method to update your label :
private void UpdateLabel(string tekst)
{
if (label.Dispatcher.CheckAccess() == false)
{
updateLabelCallback uCallBack = new updateLabelCallback(UpdateLabel);
this.Dispatcher.Invoke(uCallBack, tekst);
}
else
{
//update your label here
}
}