C# Updating GUI from a static function

[MichK]

Hello,

I'm new in C#, and I'm working on some application to do direct audio recording and realtime plotting on screen. Now I'm having a lot of trouble to update the screen yet, it has been taking me almost a week now and been searching everything without result. I hope somebody could help me here..

The detailed problem is as followed:

I have a form and within this form I declared a callback function which is (and has to be) declared as a static to avoid certain "CallbackOnCollectedDelegate" errors. This is handled by initialising the callback as a new type (and this certain type expects a static).
The audio (callback) runs fine, if it's declared as a static though.

Now I receive constant new information within this callback routine and I'd like to send it to the form (gui).
I understand I should use begininvoke to make sure there are no crossthreading problems. Next I try to update the gui from the function which I hand to the begininvoke method.
Yet now the compiler tells me I have to give a static function to the begininvoke method (probably because this begininvoke is within the static callback (which has to be static)).
Now that would be ok, yet if I make the begininvoke-function also a static function, I cannot reach the gui anymore (the "this" keyword is not allowed anymore).
Does this mean it's impossible to reach the GUI from a static function?
Or do I have to make the form also a static? (I read that this is not possible).
Does anyone know how I could tacle this problem? I would be very grateful!

Here's some of the code (without unrelevant stuff):

namespace APItest
{
    public partial class Form1 : Form   
    {
 
        delegate void UpdateProgressDelegate();
        unsafe public static void* stream;
        unsafe public static PA19.PaStreamCallback callback = new PA19.PaStreamCallback(PACallback);     
 
//-----------------------------------------------------------------------------------------------------------------------------
 
        unsafe public static int PACallback(bla...)
        {
 
            MethodInvoker mi = new MethodInvoker(this.UpdateProgress);
            this.BeginInvoke(mi);
 
 
            return 0;
        }        
//-----------------------------------------------------------------------------------------------------------------------------
 
        void static UpdateProgress()//int time, ref int refParam
        {
 
            this.label1.Text = Convert.ToString(count++);         
        }
//-----------------------------------------------------------------------------------------------------------------------------
 
        unsafe private void cmdStart_Click(object sender, EventArgs e)
        {
 
            error = PA19.PA_OpenDefaultStream(callback);
            error = PA19.PA_StartStream(stream);
        }
 
    }
}
 

Thanks.
-Michiel

[yousefla]

Your problem is you can't go from object data from a static method. But remember going the opposite way, you CAN access static data from object space. So having said that... One thing comes to my mind is to make a static ArrayList that represents the data records you get from the static callback, Now you can dump data you get on the call back into this ArrayList (Producer)

Next, initiate a worker Thread from your Main form that has a dedicated loop to check the static ArrayList and consume it's data (Consumer). Notice that you are able to access static data from the main form, so that's not a problem.

Next from within your worker thread, you can pass the consumed records to BeginInvoke to update the GUI.

Be sure to **lock** your multi-threaded static ArrayList to prevent deadlocks. And you need to lock it from the SynRoot object to avoid synchronization problems.

Hope this helps...

[MichK]

Hi,
The scheme you mentioned is a posibillity I actually wanted to avoid. I have this allready partly implemented, yet I don't want to be polling my Buffer-array's as the worker-thread shall have to work at very high-speed to provide a smooth update of data to my GUI. This consumes a lot of CPU, so the begininvoke method or some sort of flagging-method would be ideal..
I noticed it's possible to acces form's within a static if you make an instance first though, yet I can't seem to get the instanced form directly linked to the actual form.

unsafe public static int PACallback
{
  Form1 UserForm = new Form1(); 
  //This should not be "new", yet the compiler won't accept:
  //Form1 UserForm = Form1();
  //Why not? 
 
  MethodInvoker mi = new MethodInvoker(UpdateProgress);
  UserForm.BeginInvoke(mi);
}
 

I'm looking to a semaphore solution now, maby that could solve the problem.

Thanks
-Michiel

[MichK]

I've got the solution.

It amazes me how little is known nor written about this problem, absolutely turned the internet upside-down for over a week without finding any solution nor even people with similar problems.

So it seems I have kind of a pioneering solution to this problem here and therefore I'd like to post it here, I think it would help other people a great deal having similar problems getting very frustrated as I've been these weeks.

The solution is actually pretty simple and solid, although I was actually suprised it worked.

I declared a public static Thread with a non-static callback (apperantly this is allowed).
That's the main gimmick.

Then I start the thread in some global start event (for ex. form_load), yet I suspend/hold the thread immediately and as soon as the Audio (static) callback is called I resume the (non-static) thread-callback.
The thread-callback has a while loop with a thread.suspend at the end, thus acting in "one-shot" mode.
Every time the audio-callback is called it resumes the thread again, thus doing one cycle.
I can, of coarse, do a begininvoke in this non-static thread to make sure the GUI is then called properly and there it is: a working method to call a non-static function from a static thread, updating a GUI in sync.
Who would've known it could be done. not a lot of people obviously...

It's working great now and as far as I can tell it's rock solid.

[ghostrunner]

Hey.

I can see it's quite an old thread this, but ill try anyway.
Would it be possible to se a code example of this solution?

/Rasmus

@MichK