Time in TextBlock WPF

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1.00/5 (1 vote)

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Hello again.

I'm starting to use WPF and now I have a problem.

I need to do a TextBlock with the actual time. I tried specifying in the code:

Textblock1.Text=DateTime.Now.ToShortTimeString();

But when execute the form appears this error:

The calling thread cannot access this object because a different thread owns it.

How I can show the now time?

Thanks

Posted 22-Jul-11 14:53pm

TANicox

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3 solutions

Solution 1

See this to learn about the WPF threading model and accessing UI elements from threads other than the UI thread...

Threading Model[^]

Posted 22-Jul-11 15:22pm

Mark Salsbery

Comments

Sergey Alexandrovich Kryukov 23-Jul-11 1:40am

Makes sense, my 5. I provided more detailed explanation in my answer, please see.
--SA

Solution 2

Try using the Dispatcher as shown here[^].

Posted 22-Jul-11 19:03pm

Abhinav S

v2

Comments

Sergey Alexandrovich Kryukov 23-Jul-11 1:40am

Correct, my 5. I provided more detailed explanation in my answer, please see.
--SA

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When answering a question please:

Read the question carefully.
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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-07-22T19:39:00

Solution 3

More details to understand correct answer by Abhinav and Mark:

You cannot call anything related to UI from non-UI thread. Instead, you need to use the method Invoke or BeginInvoke of System.Windows.Threading.Dispatcher (for both Forms or WPF) or System.Windows.Forms.Control (Forms only).

You will find detailed explanation of how it works and code samples in my past answers:
Control.Invoke() vs. Control.BeginInvoke()[^],
Problem with Treeview Scanner And MD5[^].

See also more references on threading:
How to get a keydown event to operate on a different thread in vb.net[^],
Control events not firing after enable disable + multithreading[^].

—SA

Posted 22-Jul-11 19:39pm

Sergey Alexandrovich Kryukov

Comments

Abhinav S 23-Jul-11 2:07am

5 for the detailed explanation.

Sergey Alexandrovich Kryukov 23-Jul-11 2:16am

Thank you, Abhinav.
--SA

TANicox 23-Jul-11 13:05pm

Please you can specify an example with this? Because I'm novice and I don't understand so much

Mark Salsbery 23-Jul-11 18:53pm

Something like this?

Textblock1.Dispatcher.BeginInvoke(new Action(() =>
{
Textblock1.Text = DateTime.Now.ToShortTimeString();
}));

TANicox 23-Jul-11 19:14pm

Yes! I did it differently, but I'll use this because it is more shorter

Sergey Alexandrovich Kryukov 24-Jul-11 0:28am

Thank you for answering, Mark.
Probably this would be a bit better:

Textblock1.Dispatcher.BeginInvoke(new Action<TextBlock>((textBlock) => {
textBlock.Text = DateTime.Now.ToShortTimeString();
}), Textblock1);

In this form anonymous delegate works only with explicit parameters not using free variable.

Quote:
"There is no such thing as free variable" :-)

--SA