creating a UI in background thread WPF?

Question

I tried following:

var task = new Task(() =>
    {
       for (int i=0; i<10; i++) {
          //Create new Grid HERE
          // Add Table with some dynamic data here..
          // print the above Grid here.
        }

    });

task.ContinueWith((previousTask) =>
    {
        label.Content = printerStatus(); // will return "Out of Paper", "printing", "Paper jam", etc.
    },
    TaskScheduler.FromCurrentSynchronizationContext());

label.Content = "Sending to printer";

It returns following error: The calling thread must be STA, because many UI components require this..

The error occurs when it tries to create a new UI object Grid.

How can i fix this? Let me know if there is any other way arround!

Community · Accepted Answer · 2017-05-23 11:59:09Z

4

You cannot create UI objects on different thread than the main UI thread because as soon as you add them to the UI, it tries to set the Parent property, and a thread in WPF cannot modify objects that were created on a different thread.

Instead, I'd recommend creating a list or collection of the Grid's Data on the 2nd thread, and binding it to the UI using something like an ItemsControl. This will keep all UI objects on the main UI thread, while background processing can be done on a background thread.

To update a UI object from a background thread, such as your status label, I'd recommend using the Dispatcher like lawrencealan's answer suggests. The Dispatcher is WPF's internal message queue for the main UI thread

edited May 23, 2017 at 11:59

CommunityBot

11 silver badge

answered Dec 29, 2011 at 15:28

Rachel

133k67 gold badges316 silver badges513 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

WitVault Over a year ago

possible to add any examples for this?

Nick Butler · Accepted Answer · 2011-12-29 11:57:36Z

2

Tasks use thread pool threads, which are in a MTA.

If you want a background STA thread, you will have to create one yourself and explicitly set the ApartmentState.

Thread t = new Thread( ... );
t.SetApartmentState( ApartmentState.STA );
t.Start();

answered Dec 29, 2011 at 11:57

Nick Butler

24.5k4 gold badges51 silver badges72 bronze badges

4 Comments

user995387 Over a year ago

can you show me the sample code. I am very new to this technology.

user995387 Over a year ago

And how can i know the task is complete using this?

Nick Butler Over a year ago

I suggest reading Joe Albahari for the basics. You have to use Threads not Tasks if you want an STA, so you don't have ContinueWith. You will have to use Dispatcher.Invoke from inside your thread method instead.

Security Hound Over a year ago

@user995387 - Unless you report the progress of the thread, you have no way of knowing when the thread will be completed, thats entirely up the the scheduler.

Larry Williamson · Accepted Answer · 2011-12-29 11:57:57Z

1

Using the Dispatcher for the label and Invoke might help:

label.Dispatcher.Invoke(
      System.Windows.Threading.DispatcherPriority.Normal,
      new Action(
        delegate()
        {
          label.Content = printerStatus();
        }
    ));

answered Dec 29, 2011 at 11:57

Larry Williamson

1,1226 silver badges19 bronze badges

5 Comments

user995387 Over a year ago

It is not able to create Grid! it shows error in Grid object whlie creating it.

crypted Over a year ago

What do you mean by grid, you mean DataGridView or Simple Grid data structure.

user995387 Over a year ago

WPF Grid. that holds the UI contents..msdn.microsoft.com/en-us/library/system.windows.controls.grid.aspx

Larry Williamson Over a year ago

When modifying any sort of UI objects that are not created in the same thread, from within another thread or background worker, you need to use a Dispatcher. I think maybe your Grid creation is another problem, unless you are attempting to modify an existing UI object.

user995387 Over a year ago

here is what i wanted to do: stackoverflow.com/questions/8671277/correct-method-of-threading

Collectives™ on Stack Overflow

creating a UI in background thread WPF?

3 Answers 3

1 Comment

4 Comments

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

4 Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related