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I have async operation, in which I call a non-void method:

var result = _controller.SendInvoice(this.ParentForm);

I was getting error "Cross-thread operation not valid: Control 'ParentForm' accessed from a thread other than the thread it was created on"

I've managed to fix it by writing code like this:

ParentForm.Invoke(new MethodInvoker(delegate { _controller.SendInvoice(ParentForm); }));

The problem is that I have to get the return result of the method SendInvoice, but the "solution" above does not solving it for me because it doesn't return value from SendInvoice() method.

Jan J.
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  • Try `var result = ParentForm.Invoke(() => _controller.SendInvoice(ParentForm));`. The MethodInvoker delegate does not support return values. – Klaus Gütter Nov 21 '22 at 09:14
  • Does this answer your question? [Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on](https://stackoverflow.com/questions/142003/cross-thread-operation-not-valid-control-accessed-from-a-thread-other-than-the) –  Nov 21 '22 at 09:17

2 Answers2

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You probably want to send only data not all form. Create type Invoice and copy data from form to it, and send it to your method.

Invoice invoice;
//Here copy data
_controller.SendInvoice(invoice);
BWA
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The problem is in .Net Framework, you cannot access ParentForm from a non-UI thread (exactly the thread the form is created), but you can call Invoke on the control. This method is also able to return a value.

var result = (RETURN-TYPE)_controller.Invoke(
    new Func<RETURN-TYPE>(() => _controller.SendInvoice(ParentForm)));
shingo
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  • Unfortunately, I have "specific" controller class, where Invoke is protected and it HAVE to stay like this. Thanks though – Jan J. Nov 21 '22 at 09:59