Dispatcher.Invoke inside a delegate

Question

I have something I must do in the UI thread. Therefore I do that :

        Dispatcher.Invoke(() =>{ what I must do in the UI thread}

When I put this line inside a function, it works but it doesn't work inside a delegate like in this example:

public Action f = () => // it does'nt work
{
    Dispatcher.Invoke(() => {what I must do in the UI thread });
 }

public void ff() // it works
{
     Dispatcher.Invoke(() => { what I must do in the UI thread });
}

The error is the following :

a field initializer can not reference the non-static-field, method or property DispatcherObjet.Dispatcher

Use `async/await` instead of `Dispatcher.Invoke` Refactor your code so you *don't* mix up background processing and UI updates. If you want to report progress use `Progress` — Panagiotis Kanavos, Oct 10 '18 at 07:09

bommelding · Accepted Answer · 2018-10-10T06:45:19.143

2

You cannot reference this.Dispatcher in an initializer.

The following should work or at least move the error to what I must do in the UI thread

public Action f = () => // it should work
{
    Application.Current.Dispatcher.Invoke(() => {what I must do in the UI thread });
}

edited Oct 10 '18 at 06:45

answered Oct 10 '18 at 06:38

bommelding

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Have a idea or documentation that explains why your solution works and not mine? – Pierre-olivier Gendraud Oct 10 '18 at 06:50
Just follow your [error message](https://stackoverflow.com/questions/14439231/a-field-initializer-cannot-reference-the-nonstatic-field-method-or-property). It's not about the Dispatcher. – bommelding Oct 10 '18 at 06:55

Daniel Hilgarth · Answer 2 · 2018-10-10T06:43:51.690

0

You need to initialize the field f in the constructor:

public class YourClassName
{    
    public Action f;

    public YourClassName()
    {
        f = () => 
        {
            Dispatcher.Invoke(() => {what I must do in the UI thread });
        }
    }
}

What's going on is that f is a field of your class. Field initializers like the one you used have no access to instance members of the class but only to static members.
If you need to have access to instance members, you need to initialize the field in an instance member like the constructor.

edited Oct 10 '18 at 06:43

answered Oct 10 '18 at 06:34

Daniel Hilgarth

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Hello thank you for your help. I have tried that but it doesn't work. I have still the same error. – Pierre-olivier Gendraud Oct 10 '18 at 06:36
That's not possible. Please show the exact code you have. – Daniel Hilgarth Oct 10 '18 at 06:37
@DanielHilgarth - it's not abundantly clear that you are using a constructor here. Maybe add the surrounding class. – bommelding Oct 10 '18 at 06:39
Well, I mention the constructor *twice*... But still, thanks for the hint, changed the answer – Daniel Hilgarth Oct 10 '18 at 06:43
@DanielHilgarth my code is a bit long. It seems to works with Application.Current.Dispatcher.Invok instead of Dispatcher (therefore system.windows.threading.dispatcher). Another i haven't mention is that my action is public readonly. – Pierre-olivier Gendraud Oct 10 '18 at 06:46
Nothing you say prevents you from using the approach I explained – Daniel Hilgarth Oct 10 '18 at 06:47
@DanielHilgarth Ok I will put my code in my question – Pierre-olivier Gendraud Oct 10 '18 at 06:54
If the other answer works for you, no need to do that – Daniel Hilgarth Oct 10 '18 at 06:58

Dispatcher.Invoke inside a delegate

2 Answers2