Dispatcher.invoke problem in a class : C#

Question

here is part of my code:

public void refreshShowCase()
{

    for (int i = 0; i < 12; ++i)
    {
        bitmapImage[i] = new BitmapImage(new Uri(posterURLCollection[i]));
        image[i] = new Image { Source = bitmapImage[i] }; //Error occurs here****
    }
}

when I run this I get this error: The calling thread must be STA, because many UI components require this.

So I add my code inside Disapther.Invoke

this.Dispatcher.Invoke((Action)delegate
{
   BitmapImage[] bitmapImage = new BitmapImage[14];
   Image[] image = new Image[14];

   //Do a loop for defining Bitmaps sources
   for (int i = 0; i < 12; ++i)
   {
         bitmapImage[i] = new BitmapImage(new Uri(posterURLCollection[i]));
         image[i] = new Image { Source = bitmapImage[i] };
   }
}

Now I have this error: 'Dispatcher' doesn't exist in the current context!

How should I solve this? Please help.

Update1: mentioned code is inside void of a class which I have created!

Does System.Windows.Application.Current.Dispatcher.Invoke work? — Adam, Sep 14 '18 at 15:34
@Adam: When I use that I get this: 'Current' does not exist in the type 'Application' — E. Mamaghani, Sep 14 '18 at 15:37
@SoumenMukherjee: When I don't use Dispatcher I get runtime error which I have mentioned: The calling thread must be STA, because many UI components require this. But when I use Dispatcher a red line goes under the `This.Dispatcher` and says: 'Dispatcher' doesn't exist in the current context! — E. Mamaghani, Sep 14 '18 at 15:44
My crystal ball says that you wrote a UWP app, not a WPF app. https://stackoverflow.com/questions/16477190/correct-way-to-get-the-coredispatcher-in-a-windows-store-app — Hans Passant, Sep 14 '18 at 15:58
@HansPassant: In app's main class this.Dispatcher works fine! this problem is for that special class. — E. Mamaghani, Sep 14 '18 at 16:10

score 2 · Accepted Answer · answered Sep 14 '18 at 15:47

2

In your question, you are using this.Dispatcher.Invoke((Action)delegate inside of a custom class. this refers to functions inside of that class. Your custom class does not have Dispatcher.

Instead use: App.Current.Dispatcher.Invoke((Action)delegate and make sure this your custom class containing this code falls under your App namespace.

answered Sep 14 '18 at 15:47

David Bentley

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How should I make sure that the class falls under App namespace? Can you please specify? – E. Mamaghani Sep 14 '18 at 15:51
When I use this `App.Current.Dispatcher.Invoke((Action)delegate` a line goes under `Current` and says 'Current' doesn't exist in the App context! How can I solve this? – E. Mamaghani Sep 14 '18 at 15:56
If this class is inside of a .cs file, just make sure it is inside the curly braces for `namespace myAppname` and you should be fine. – David Bentley Sep 14 '18 at 15:56
What .net version and are you using a console app or windows app? Is this a WPF or UWP app? – David Bentley Sep 14 '18 at 15:58
it is WPF application – E. Mamaghani Sep 14 '18 at 16:04
Then it should be working. Where is class located in your application? – David Bentley Sep 14 '18 at 16:05
Take a look at this. this is how the class is located! [IMG](https://ibb.co/dZu8up) – E. Mamaghani Sep 14 '18 at 16:08
@E.Mamaghani Also post the top portion of your app.xaml.cs code. – David Bentley Sep 14 '18 at 16:41
I have created another class exactly same with the last one and it now accepts and works fine! don't know really why the last class had problem! – E. Mamaghani Sep 14 '18 at 16:46
@E.Mamaghani You may still want to compare the files to see what is different for your own future reference. Please mark the answer as accepted also. – David Bentley Sep 14 '18 at 16:53

Dispatcher.invoke problem in a class : C#

1 Answers1