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The calling thread cannot access this object because a different thread owns it.' error in Thread wpf

I have Window 1 in which on button click i am opening Window 2 in new thread.
Following is my code
private void Button_Click_2(object sender, RoutedEventArgs e)
{
Thread thread = new Thread(() =>
{
Scanner w = new Scanner();
w.Show();
w.Closed += (sender2, e2) =>
w.Dispatcher.InvokeShutdown();
System.Windows.Threading.Dispatcher.Run();
});
thread.SetApartmentState(ApartmentState.STA);
thread.Start();
}
Window 2 has form I am getting form values on Button click
private void EnterProduct(object sender, RoutedEventArgs e)
{
var data = ProductDetailsData;
LoadCurrentBetween objMain = new LoadCurrentBetween(); //new MainWindow();
objMain.fillorderform(data);
}
on button click of window 2 i am passing values of form to another View
public void fillorderform(dynamic data)
{
this.Dispatcher.Invoke(() =>
{
LoadCurrentdetails.Part = data.Part;
LoadCurrentBetween loadCurrentbtw = new LoadCurrentBetween();
Switcher.Switch(loadCurrentbtw);
});
} public static class Switcher
{
public static MainWindow pageSwitcher;
public static void Switch(UserControl newPage)
{
pageSwitcher.Navigate(newPage);
}
}
Following code is giving error at "this.Content = nextPage;"
The calling thread cannot access this object because a different thread owns it.
public void Navigate(UserControl nextPage)
{
this.Dispatcher.Invoke(() =>
{
var aa = nextPage.Dispatcher.CheckAccess();
this.Content = nextPage;
});
}
I have seen similar Questions asked by other developers but i am not getting how to fix.
pls help

WPF is very strict (compared to Windows forms) about requiring methods which update UI elements to be done on the main/UI thread. So you definitely want both windows to be in the main/UI thread. The error that you are seeing is what happens if you try to do UI work in WPF from a different thread, so you absolutely have to stop doing that. It's OK to have multiple windows open, all on the same UI thread.
If one of your windows is doing heavyweight processing that makes the UI lock up, then the easiest thing is probably to add the async keyword to your button click event, and put the work you are doing in another method which has an async keyword. Then, when you call the helper method, you use the await keyword.
I agree with others that BackgroundWorker and Task are two other ways to accomplish heavyweight processing in a background thread while still having a responsive UI. Tasks are easier to use than BackgroundWorker.
If you are using a BackgroundWorker, it may be good enough to use the RunWorkerCompleted event. If so, look at this post: How to use WPF Background Worker. If you are using a BackgroundWorker and you need to call a custom method in your UI class from the background thread, then pass the Dispatcher object for your window/dialog to the background thread (or get access to it some other way), and when it needs to call back into the UI, use Invoke with the Dispatcher object. By using Invoke, the method you are calling from the background thread will be executed on the UI thread.

WPF NotifyPropertyChange from different thread

I have my VM implemented INotifyPropertyChanged interface. I created another thread T for populating a list that I bind to Xaml. After list is populated, I call PropertyChanged in thread T, and my UI got refreshed correctly.
My question is in what case I would need to use Dispatcher? Why I don't need to use Dispatcher in my case? I thought Dispatcher is used when the code in other thread want to notify the changes to the UI thread by enqueuing the changes to the UI refresh queue, such as adding items to ObservableCollection from another thread, and UI thread will then pull data from the queue.
private List<string> _ListData;
public List<String> ListData
{
get
{
if (_ListData == null)
Initialise( () => ListData = ReturnSlow());
return _ListData;
}
set { _ListData = value; }
}
private List<string> ReturnSlow()
{
List<string> Test = new List<string>();
Test.Add("1");
Test.Add("2");
Thread.Sleep(2000);
return Test;
}
public void Initialise(Action initialiser)
{
Task t = new Task(() =>
{
initialiser();
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("ListData"));
});
t.Start();
}

Your app has a main UI thread (usually ManagedThreadId==1). If you want to update the UI from an event that gets pull on some other thread you must use the dispatcher. A useful test here is the Dispatcher.CheckAccess() method that returns true if code is on UI thread and false if on some other thread. A typical call looks something like:
using System.Windows.Threading; // For Dispatcher.
if (Application.Current.Dispatcher.CheckAccess()) {
network_links.Add(new NetworkLinkVM(link, start_node, end_node));
}
else {
Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Normal, new Action(()=>{
network_links.Add(new NetworkLinkVM(link, start_node, end_node));
}));
}
If you're in the main window you can use:
Dispatcher.BeginInvoke(...
If you're in someother context eg a view model then use:
Application.Current.Dispatcher.BeginInvoke(
Invoke vs BeginInvoke
Use Invoke if you want the current thread to wait until the UI thread has processed the dispatch code or BeginInvoke if you want current thread to continue without waiting for operation to complete on UI thread.
MessageBox, Dispatchers and Invoke/BeginInvoke:
Dispatcher.Invoke will block your thread until the MessageBox is dismissed.
Dispatcher.BeginInvoke will allow your thread code to continue to execute while the UI thread will block on the MessageBox call until its dismissed.
CurrentDispatcher vs Current.Dispatcher!
Be ware of Dispatcher.CurrentDispatcher as my understanding of this is that is will return a Dispatcher for the current thread not the UI thread. Generally are you interested in the dispatcher on the UI thread - Application.Current.Dispatcher always returns this.
Additional note:
If you are finding you are having to check dispatcher CheckAccess often then a useful helper method is:
public void DispatchIfNecessary(Action action) {
if (!Dispatcher.CheckAccess())
Dispatcher.Invoke(action);
else
action.Invoke();
}
Which can be called as:
DispatchIfNecessary(() => {
network_links.Add(new NetworkLinkVM(link, start_node, end_node));
});

Dead lock with backgroundWorker

I faced with one interesting moment when working with multithreading.
I have two threads. In main thread I create layout and add to it control,in second thread I create another control and add to the same layout. It works fine, but second thread works a bit longer then main. So main should wait for second thread.I use for this AutoResetEvent and got DeadLock. Below I describe code what I use:
private static AutoResetEvent resetEvent = new AutoResetEvent(false);
private BackgroundWorker backgroundAdvancedViewWorker = new BackgroundWorker();
private delegate void ShowViewDelegate();
public void Run()
{
MainGeneralReportForm mainForm = ObjectFactory.GetOrCreateView<IMainGeneralReportForm>();
backgroundSimpleViewWorker.RunWorkerAsync(_mainForm);
GeneralReportFormatView formatView =
ObjectFactory.ShowView<IGeneralReportFormatView>()
resetEvent.WaitOne();
DoSomething(advancedSearchView);
}
private void backgroundAdvancedViewWorker_DoWork(object sender, DoWorkEventArgs e)
{
MainGeneralReportForm mainForm = e.Argument as MainGeneralReportForm;
if (mainForm!= null && mainForm.InvokeRequired)
{
mainForm.BeginInvoke(new ShowViewDelegate(() =>
{
advancedSearchView =
ObjectFactory.ShowView<IGeneralReportAdvancedSearchView>();
resetEvent.Set();
}));
}
}
}
If main thread doesn't wait for second thread, the application throws NullReferenceException.
Is exist any solution or workaround of this problem?

You block main thread by resetEvent.WaitOne(); and at the same time trying to schedule work item back to main thread with BeginInvoke (which indeed can't run as main thread is waiting).
Not sure what right fix would be, but blocking on main thread is not really an option.
Maybe some "state" field on the form may be enough. Or maybe running DoSomething(advancedSearchView); from BeginInvoke callback (instead of resetEvent.Set();).
Note: if you are on 4.5 you can consider using async/await instead of manual threading.

Windows Phone 7 - How to Update UI From while Loop?

How would I update the UI in my Windows Phone app from a while, foreach, for, etc loop?

Have you considered using additional thread for this?
public MainPage()
{
InitializeComponent();
Thread thread = new Thread(() => ReadFile(/*params*/));
thread.Start();
}
private void ReadFile(/*params*/)
{
while(/*condition*/)
{
/* READ FILE */
//send task to UI thread to add object to list box
Dispatcher.BeginInvoke(() => listBox1.Items.Add("YOUR OBJECT"));
}
}
Long term action is happening in non-UI thread, what makes that UI thread doesn`t get frozen. In every loop iteration, non-UI Thread sends action via Dispatcher.BeginInvoke to UI thread to add new object to listbox.

Wait thread question

I have a UserControl with a tree on it. It uses multithreading to add nodes to it. I have a function called Expand which I need to execute after filtering completed and since I'm a newbie with multithreading I'm not sure how to do that. Here's my code:
class MyClass : UserControl
{
private Thread nThread;
private bool searchLoadCompleted = false;
private void Filter()
{
ClearTree();
this.nThread = new Thread(new ParameterizedThreadStart(AddFilteredResultsToTree));
this.nThread.IsBackground = true;
this.nThread.Start(someParameter);
}
private void AddFilteredResultsToTree(int someParameter)
{
myTree.Invoke(new MethodInvoker( ()=> this.searchLoadCompleted = false ));
myTree.Invoke(new MethodInvoker( ()=> AppendNode(......) ));
myTree.Invoke(new MethodInvoker( ()=> this.searchLoadCompleted = true ));
}
private void Expand()
{
}
}
I tried to add nThread.Join() into Expand() but it got stuck indefinitely. What should I do?

If the singlethreaded version of this is:
ClearTree();
AddFilteredResultsToTree(someparameter);
Expand();
Don't bother going multithreading, just do it on the same thread. The point of using multithreading there would be to let the main thread handle UI events, if you join the thread then you're basically just launching a background thread while freezing (not doing any work) in the main thread. Note that by calling Invoke you're actually delegating the execution of AddFilteredResultsToTree to the main thread anyway.
I'd suggest you simply call Expand from AddFilteredResult and use the Dispatcher to update the UI if needed or.
Another way to go (best in my opinion) would be to use the Async Pattern for this (example and tutorial here), and then on the AsyncCallback update the UI.

Calling Invoke will block both the GUI thread and your worker thread so there won't be any performance improvement over code without a worker thread.