LabVIEW
.NET DLL Event Handling . What am I doing wrong
Hello everyone,
I am writing a program to USB interface with a splicing machine.
The connection is working properly and I am able to send receive/commands to the machine.
My problem is the event handling. I tried different things to fix this issue and tried different examples including the NI default ones. These examples worked on my machine so I don't think that the problem is specific to my software config.
Basically, I am loading the DLL in Labview, callign the constructor then using Reg Event Callback to register the events:
I select the event ( Attached in this case) right click on the VI ref and create the call back
I put in a one button messageBox for debugging..
The Attached event is supposed to fire when the USB machien is connected.
I never got the Callback VI to execute and I don;t know how to troubleshoot. I tried a debugger that I found online ( debugView) to see if something happens in the background when I connect disconnect the machine and I actually see this everytiem I plug/unplug the USB device:
[8600] FMAPP: Debug function is disable
[8600] FMAPP is running
[8916] FMAPP: Debug function is disable
[8916] FMAPP is running
I hope someone call show me how to troubleshoot this issue further cause I am running out of ideas... A C# event handler works just fine and I am able to capture these events.
Some people reported a NULL parameter issue and it looks like an unsolved issue based on the documentation I found so far. I am not sure I have this problem but I can't think of a way to confirm this. Some people are saying that they had to come up with a wrapper DLL to go around that issue with Null parameter in event calls. I wish someone will help me to start somewhere regardign this as well.
Thanks in advance for helping !
Alright, I ve got sometime this week to go and investigate this issue further. I tried to do what other people did to solve this issue : a wrapper DLL
Basically, instead of handling the event fired by my device DLL directly in Labview, I created an intermediate DLL that will capture that event and fires a second event that does not pass NULL in argument and therefore LabVIEW can handle.
I am testing my wrapper DLL with C# then Labview. I got everything to work on C# but not with LabVIEW for a reason I still don't know.
The Device DLL fires two events: “attached” and “detached”, when the device is connected/disconnected to a USB port.
This event will is captured in the wrapper DLL and triggers usb_attached method:
Usb.Attached += new EventHandler(usb_attached);
Here is the usb attached method declaratuion:
public void usb_attached(object sender, System.EventArgs e)
Again, this event cannot be handled in Labview diretly because the System.EventArgs object is passing a NULL variable.
The work around is to call another event that will have something other than Null in parameters.
So I am creating
USBstatusClass that will have that event. I am also creating my own USBconnectionArgs class that evherits from System.EventArgs and that will contain event data.
In the constructor of the USBstatusClass, I am attaching the device DLL events and forwarding the call to my newly created event.
Here is the code for the entire wrapper DLL.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WrapperDLL
{
public class USBconnectionArgs : EventArgs
{
private string USBstatus;
public string status
{
set
{
USBstatus = value;
}
get
{
return this.USBstatus;
}
}
}
public class USBstatusClass
{
public event USBconnectionHandler USBevent;
public delegate void USBconnectionHandler(USBstatusClass m, USBconnectionArgs e);
USBconnectionArgs usbStatus = new USBconnectionArgs();
public USBstatusClass(UsbFsm100ServerClass Usb)
{
Usb.Attached += new EventHandler(usb_attached);
Usb.Detached += new EventHandler(usb_detached);
MessageBox.Show("Hello 1");
}
public void usb_attached(object sender, System.EventArgs e)
{
USBconnected();
MessageBox.Show("Hello 2");
}
public void usb_detached(object sender, System.EventArgs e)
{
USBdisconnected();
}
public void USBconnected()
{
if (USBevent != null)
{
usbStatus.status = "YES";
USBevent(this, usbStatus);
}
}
public void USBdisconnected()
{
if (USBevent != null)
{
usbStatus.status = "NO";
USBevent(this, usbStatus);
}
}
}
}
In C# this DLL works perfectly. You can find the code in the attachment for the receiver application that will capture the event created by USBstatusClass. Note that I am inserting few messageboxes in the code for debugging.
My issue is really with Labview. The constructor loads the function perfectly. But when the device is connected, there is not event captured.
When I call the USBconnected() function from Labview, the event got actually fired and captured in Labview. However, the same event is not triggered when the USB is connected. Again, this wrapper DLL works perfectly in C#..
Here is my Labview Code:
First I use user32.dll ( FindWindowA() ) method to get a IntPtr anbd initialize the Device DLL ( call the constructor), then I init the driver using the InitDriver invoke node.
I then Call the constructor of my status class and register the event into. I am putting a messageBox in the CallBAck VI to troubleshoot.
The same concept is written in C# ( see code below:
namespace WrapperForm
{
public partial class Form1 : Form
{
USBstatusClass m;
private UsbFsm100ServerClass Usb;
public Form1()
{
InitializeComponent();
}
private void Form1_Load_1(object sender, EventArgs e)
{
Usb = new UsbFsm100ServerClass(this.Handle);
USBstatusClass m = new USBstatusClass(Usb);
m.USBevent += new USBstatusClass.USBconnectionHandler(HeardIt); // New event
}
private void HeardIt(USBstatusClass m, USBconnectionArgs e)
{
label1.Text = e.status;
if (e.status == "YES")
{
label1.ForeColor = Color.Blue;
}
else label1.ForeColor = Color.Silver;
}
}
}
So when I manually trigger the event created by USBstatusClass, I see the messageBox appearing. But when I physically connect the machine to USB, C# detects it and fires the event, but this does not happen in LAbview.
PLEASE HELP. I KIND OF RUN OUT OF IDEAS 
