Monitoring a Variable

[Solidad]

I am trying to make a program the will monitor if the certain variable changes.

lets say if the default value is 0, the program will just listen, but when the value changes to 1. something will happen.

here is what i have thought

Do Until Exit_button is clicked

If val != 0 Then
   Execute Statement
End if

Loop

how can i do this? in VB.net if its just that, the program wont let me do anything. since it is busy with the endless loop.

[daniel142005]

The reason it does this is because the application is divided into threads, you are executing an endless loop on the form thread, which causes it to lock up. What you need to do is create a sub thread (multi-threading) for the application. Take a look at this, maybe it will help:
http://www.dreamincode.net/code/snippet875.htm

Alternatively, you could use a Timer and set the interval to 1 sec and in the timer tick's code you can handle what happens if it changes.

Side note, why not just use an on click method for the button instead of waiting for the button to be clicked by using loops?

[Solidad]

since i am monitoring a parallel port. when the value on that status port changes. it should run a event and send a signal to the motors drivers. the trigger is a laser and a photo sensor when the laser light is blocked a change in the status port will happen. since we don't know when will that happen it should be monitored.

[daniel142005]

Ah, i just kinda glanced at the code, yeah try running the loop in another thread with the background worker and see if that helps you any. The timer is probably easier to implement but is kind of a work around and may cause problems later on.

[Solidad]

i try running the background worker component, and now i need to periodically to produce a report. like a text box text that says "Monitoring" every lets say 1 sec. since BGW uses a different thread i can't just change the values of the texbox, and the RunComplete event of the BGW will only happen when i cancel or finish the task, how can it be overcome?

[daniel142005]

Your going to need to use delegates and invokes to communicate between threads. Check here: http://addressof.com/blog/archive/2005/02/10/1287.aspx it has some tutorials on Threading in VB .NET.