C# InvokeRequired with property getter

Question

I would like to make my getter thread safe. When I do this, I get an error:

public ApplicationViewModel SelectedApplication
    {
        get
        {
            if (InvokeRequired)
            {
                BeginInvoke((Action<ApplicationViewModel>)SelectedApplication);
            }

            return _applicationsCombobox.SelectedItem as ApplicationViewModel;
        }
    }

I have the error:

Cannot cast expression of type 'Foo.Model.ApplicationViewModel' to type 'Action<ApplicationViewModel>'

score 6 · Accepted Answer · edited May 22 '14 at 08:21

Lots of things wrong:

you cannot use BeginInvoke, Invoke is required
you cannot use Action<>, you are returning a value so Func<> is required
you cannot also run the original code after invoking, else is required.

Which produces:

public ApplicationViewModel SelectedApplication
{
    get
    {
        if (this.InvokeRequired)
            return (ApplicationViewModel)this.Invoke(new Func<ApplicationViewModel>(() => this.SelectedApplication));
        else
            return _applicationsCombobox.SelectedItem as ApplicationViewModel;
    }
}

Hiding the thread context switches in a low-level property is usually a mistake. Invoking has lots of overhead, the resulting code may end up being very slow without a good hint of why it is so slow.

Except it's transparent to the consumer; no other method has to care how it was invoked in order to get this property in a synchronous fashion. You'd only be able to reduce the slowdown in cases where you were 100% sure the caller was on the UI thread. — KeithS, Aug 04 '11 at 17:34

score 3 · Answer 2 · answered Aug 04 '11 at 17:12

3

BeginInvoke takes a delegate.

You can write

return (ApplicationViewModel)Invoke(new Func<object>(() => applicationsCombobox.SelectedItem));

answered Aug 04 '11 at 17:12

SLaks

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score 2 · Answer 3 · answered Aug 04 '11 at 17:07

2

Try:

public ApplicationViewModel SelectedApplication
    {
        get
        {
            if (InvokeRequired)
            {
                BeginInvoke(() => { return SelectedApplication(); });
            }

            return _applicationsCombobox.SelectedItem as ApplicationViewModel;
        }
    }

answered Aug 04 '11 at 17:07

Jakub Konecki

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Thanks but now it says: "Method, event or delegate is expected" on the method SelectedApplication(); – John Aug 04 '11 at 17:11

C# InvokeRequired with property getter

3 Answers3

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