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c#invokerequired
John
John

Reputation: 4601

C# InvokeRequired with property getter

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>'

Upvotes: 2

Views: 3672

Answers (3)

Hans Passant
Hans Passant

Reputation: 941515

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.

Upvotes: 6

SLaks
SLaks

Reputation: 887453

BeginInvoke takes a delegate.

You can write

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

Upvotes: 3

Jakub Konecki
Jakub Konecki

Reputation: 46008

Try:

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

            return _applicationsCombobox.SelectedItem as ApplicationViewModel;
        }
    }

Upvotes: 2

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