How can you tell if you're on the Main UI thread? (In CF)

Question

Now unfortunately due to the fact that WinCE Usb Device Arrival / Removal exposes itself via WindowsMessages I have to ensure that a certain (non-UI) component is not created on a background thread. I would like to assert this via an exception but am lacking the code for the assertion.

This component creates a MessageWindow* and uses it to receive usb arrived/removed messages. The issue is if someone creates this component on a background thread (not necessarily; IsBackground = true) when the thread exits the window will be destroyed.

Any ideas?

*as an aside I still don't know why Form doesn't inherit from this class

Update

I think my version 1 wasn't very clear. So this is v2.

When you create a MessageWindow or a Form for that matter on a thread, when that thread exits the Window/Form is destroyed.

My component is creating a "hidden" message window to intercept some important events, ergo I do not wish for it to be destroyed. Therefore I must somehow ensure that the code that creates the form is running on the "Main UI" thread.

If possible i'd like to avoid passing down a reference to the "main" form to this component as it is (architecturally speaking) supposed to be miles away from the UI.

Update

Moving logging question to a separate Q.

Answer 1

In forms, you use the InvokeRequired property.

Answer 2

Why not create the non-UI component on a background thread and when you go to update any UI component just look to see if invokeRequired then get back on the main thread to actually do the update.

You should have nothing really tying up the main event thread, IMO.

Answer 3

You can use it in this way:

void MyCallback()
{
if (form1.InvokeRequired) { // form1 is any existing gui control
    form1.Invoke(new Action<>(MyCallBack));
    return;
}
// your logic here
}

Answer 4

Ok, I understand that you don't want for your component to "know" about the main window -- makes sense.

How about this: How about if you make sure that you always instance your component on the main thread? You component will create it's listener window on the constructor's thread.

If you do that, then you just need to make sure that you call the constructor from the main thread. I'm making some assumptions about your code, but I'm guessing that you must have some class in your architecture that knows about both the UI and your component. Create your component there, using a callback, and the main form's InvokeRequired/Invoke methods.

Answer 5

Hey there: I had an idea about your problem. This is just a random thought, and I don't know for sure whether it will work (I have not tested, nor even compiled this -- it just hit me):

What if you get the window handle of the main window of your app, then build a Control around it (I'm assuming that you have a gdi-based app, like Winforms)?

this code might not compile, but it's close (it would go into your component -- note that it would make your component require a gdi windows/winform app, as opposed to a console or WPF app).

If you do try it, I'd love to hear whether it worked for you.

using System.Diagnostics;
using System.Windows.Forms;
void Init()
{
   // get handle to the main window
   intPtr mainWindowHandle = Process.GetCurrentProcess().MainWindowHandle;
   Control mainWindow = Control.FromHandle(mainWindowHandle);
   if(mainWindow.InvokeRequired)
      mainWindow.Invoke(SetupMessageWindow);
   else
      SetupMessageWindow();
}
void SetupMessageWindow()
{
  // do your thing...
}