Using Invoke for a delegate to avoid cross threading

Glenn Patton

Hi All,

I have written a delegate to mange data from the serial port. I would like to use it to display the data on the form I have been told that I need to use an
Invoke to do this. I am having some issues using the invoke command. I have an instance of the form I wish the data to be shown on

internal static Form1 myForm1;

later in the code I am using the commands:

InputData = myComPort.ReadExisting();

myForm1.Invoke(AccessFormMarshall(InputData));

I belive I have set up the Access and Marshalling correctly. I think it is the use of the invoke command correctly.

Glenn

6 Replies

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Vulpes13y ago
Accepted answer
Can we just establish what (and where) AccessFormMarshall is.

When you said that the reference you'd been given and tried to use was:

Form1.AccessFormMarshall(recievedData);

then I thought that it must be a method in Form1.

Could it perhaps be a method in whatever form or class this code is being called from?

If it is, it may be that all you need is :

AccessFormMarshall(InputData);

if the method (as its name suggests) deals with marshalling internally.
Glenn Patton13y ago
That appears to work thanks alot!
Glenn Patton13y ago
Hi, I must being thick today but all three methods don't work. while wrapping it invoke causes an unhandled exeception.
Vulpes13y ago
Ah, it appears that AccessFormMarshall is actually a method in Form1 rather than a delegate, though I'm not sure whether it's an instance or a static method.

In that case I'd start by trying one of these as it may be that AccessFormMarshall already deals with marshalling back to the UI thread internally:

myForm1.AccessFormMarshall(InputData);

// or if static

Form1.AccessFormMarshall(InputData);

If it doesn't deal with marshalling, then I'd wrap it in the following which does:

myForm1.Invoke(new MethodInvoker(delegate()
{
// insert one of the above method calls in here
}));
Glenn Patton13y ago
Hi,
Thanks for that... but I now get:

Error 1 The best overloaded method match for 'System.Windows.Forms.Control.Invoke(System.Delegate, params object[])' has some invalid arguments C:\Users\glennp\Dropbox\PSION Emmulation\PSION Emmulation\PSION_EmmualtionA\TestBoardComms\WindowsFormsApplication152\WindowsFormsApplication152\Form1.cs 192 25 WindowsFormsApplication152
and.....
Error 2 Argument '1': cannot convert from 'method group' to 'System.Delegate' C:\Users\glennp\Dropbox\PSION Emmulation\PSION Emmulation\PSION_EmmualtionA\TestBoardComms\WindowsFormsApplication152\WindowsFormsApplication152\Form1.cs 192 40 WindowsFormsApplication152

I have included the full error message as a guide it seems to not attaching the marshall delegate properly. Sorry to be a bit vague but I appear to have got everything behind it working, but not the invoke to make it work! The reference given I have seen and tried to use was:   Form1.AccessFormMarshall(recievedData);
from that I tried to use: myForm1.Invoke(AccessFormMarshall(InputData));
Does this help at all (?)

Glenn
Vulpes13y ago
The Control.Invoke method has two overloads:

1. The first overload takes a single parameter, a delegate. This overload is designed for calling methods which don't themselves take parameters via the delegate.

2. The second overload takes two parameters, a delegate and a parameter array of type object. This overload is used to call methods which themselves take parameters via the delegate. The parameters are passed (in order) via the parameter array.

So, if (as appears to be the case) you want to call a method which takes a parameter, then you should be using the second overload rather than the first i.e.

InputData = myComPort.ReadExisting();

myForm1.Invoke(AccessFormMarshall, new object[]{InputData});