Tab Control Problem

[KenLabView]

Ok i have the following problem..when I click the run button everytime in labview i want the login  screen to show before any other tab pages..some times it works but sometimes when i stop the program at 3rd page and click run again..the program starts at 3rd page instead of the login screen..how do i correct this problem?

[MikeS81]

Hi KenLabView,

try this to assure the correct flow. see the attached picture. I recommend to use a state architecture.

Mike

Message Edited by MikeS81 on 05-05-2008 01:59 PM

[aeastet]

We ran into this same problem. If you use a property node to change the tab every thing will work like you want it to.

[smercurio_fc]

Yes, but only if it still follows proper dataflow rules, as Mike is saying. You can use a property node and it still wouldn't work properly if it was "free floating" in terms of when it can run.

[DFGray]

One final somewhat esoteric note.  If you have a choice, you should set a front panel value using the following order of precedence for methods

1. The terminal (see first example above)
2. A local variable
3. A property node (see last suggestion above)
   

The reason for this is that a property node is synchronous while the terminal and local variable are not.  When you set a Value (or Value signalling) property, LabVIEW does bounds checks, any front panel redraws, and sets the control/indicator value before returning.  When setting a terminal or local variable, the new value is posted as a change and occurs on the next UI update (about 30Hz update rate).  This makes the time usage orders of magnitude less for the terminal or local variable vs. the property node.  You do end up using a lot of single-frame sequence structures doing this to get the data flow right.  The efficiency gained is well worth the effort.

[dan_u]

I agree with the order DFGray gave. But as aeastat mentioned we also experienced that tab controls sometimes won't switch when using a local variable. Using a property node helps. Seems like a bug. I didn't check whether it's fixed in 8.5.1.