Another Noob Question: Variable Method Call?

coryco2 · 2011-03-23 08:38

Is it possible to select a method called by using a global variable?

I would like to do something like this:

VAR
BYTE MenuItem1 [7]

PUB
MenuItem1 := Method1

MenuItem1

And have Method1 (or whatever method I make equal MenuItem1 run. But I get back "variable needs an operator." What am I missing here, please? Any suggestions would be much appreciated.

StefanL38 · 2011-03-23 09:07

Hi Coryco2,

if I understand reight you want something like dependant on the value of a variable executing different methods.
therefore you can use a construction like this:

VAR
  long MethodNr

  
Pub MyMethod_choosing

  case MethodNr

    1 : Method1

    2 : Method2

    3 : Method3


Pub Method1
'....

Pub Method2
'....


Pub Method3
'....

if you want to do something else please tell in more details what you want to do.

best regards

Stefan

coryco2 · 2011-03-23 09:27

Stefan,

Thanks for the response. No, I am actually wanting to call a method by storing the name of the method to be called inside a variable array and then call the method by retrieving the name from the variable array.

My application is to be able to customize what method(s) are called from a menu (each menu item calling a different method) without changing the menu code, just the variable array values to choose what methods I want to be triggered by the menu items.

Perhaps another way of looking at it is that I would like to be able to have an "alias" for a method and call it instead of the method name itself.

StefanL38 · 2011-03-23 10:43

Aha. A way in standard SPIN for that is to define constants and code one big method-handler with a case statement.

If you are coming from c/c++ and you are looking for something like method-pointers this is not possible in standard spin.
Some members here in the forum have developed tricky ways to something similar like method-pointers.
I'm not familiar with this and especially not familiar with method-pointers in SPIN

here is the link to that thread http://forums.parallax.com/showthread.php?128397-Callbacks-and-Method-Pointers-in-Spin&highlight=Method-Pointers

best regards

Stefan

coryco2 · 2011-03-23 11:22

Aha. A way in standard SPIN for that is to define constants and code one big method-handler with a case statement.

Could you please explain a bit more what you mean? Are you saying there is some other way to call a method using constants?

Dave Hein · 2011-03-23 12:59

There is no standard way to call a method from a variable as you describe. The best standard technique is to use a case statement like Stefan suggested. You could also use the Method Pointer object that I posted in the OBEX. It is located at http://obex.parallax.com/objects/697/ .

StefanL38 · 2011-03-23 13:40

this is the basic structure of using constants and a method handler

CON
  c_MyMethodA = 1
  c_MyMethodB = 2
  c_MyMethodC = 3


VAR
  long MethodNr



PUB Main

  '..do several things

  if ...
    MethodNr := c_MyMethodB


  if ...
    MethodNr := c_MyMethodA


  if ...
    MethodNr := c_MyMethodC

  MyMethodHandler(MethodNr)

         
PUB MyMethodHandler(p_MethodNumber)

  case p_MethodNumber

    c_MyMethodA : Method_A
    
    c_MyMethodB : Method_B

    c_MyMethodC : Method_C
    


PUB Method_A
'...

PUB Method_B
'...

PUB Method_C
'...

best regards

Stefan

coryco2 · 2011-03-23 13:51

So, you are essentially assigning each method a constant number (cMyMethodA=1, etc.) , then IF or CASE testing to see if that number matches whatever value you give variable "MethodNr" and if it does it calls the corresponding PUB method? Hmm...that could work. Thanks.

Another Noob Question: Variable Method Call?

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