6. Coding

Calling functions in powerbuilder:

Syntax
{ objectname.} { type } { calltype } { when } name ( { argumentlist } )


objectname :   this(default) ; objectname
type :    function(default); event
calltype : Static(default) ; dynamic

     dynamic keyword is used when there is no need to resolve the function name at compilation. On Running, it resolves the function name & gives error if function doesn't exist.

      this is used when child object have parent reference and we want to call a child function not in parent. 

when : trigger(default) ; post

    When you post a function or event, it is added to the object’s queue and executed in its turn. In most cases, it is executed when the current script is finished; however, if other system events have occurred in the meantime, its position in the queue might be after other scripts. Its return value is not available to the calling script.

isnull vs valid 

isnull() in powerbuilder is to check for nullity of expression or variable.
IsValid() is used to check whether reference is null or initialized.

isvalid(obect type) & isnull(expression/variable).

Debugging Application

For debugging, insert breakpoints on code using right click or use keyboard shortcut to assign.

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The buttons highlighted in this is used for debugging.  The yellow pointer on code shows the current execution line on which debugger is.