Using cascaded calling and return values
PowerBuilder dot notation allows you to chain together several
object function or event calls. The return value of the function
or event becomes the object for the following call.
This syntax shows the relationship between the return values
of three cascaded function calls:
|
1 |
func1returnsobject( ).func2returnsobject( ).func3returnsanything( ) |
Disadvantage of cascaded calls
When you call several functions in a cascade, you cannot check
their return values and make sure they succeeded. If you want to
check return values (and checking is always a good idea), call each
function separately and assign the return values to variables. Then
you can use the verified variables in dot notation before the final
function name.
Dynamic calls
If you use the DYNAMIC keyword in a chain
of cascaded calls, it carries over to all function calls that follow.
In this example, both func1 and func2 are
called dynamically:
|
1 |
object1.DYNAMIC func1().func2() |
The compiler reports an error if you use DYNAMIC more
than once in a cascaded call. This example would cause an error:
|
1 |
object1.DYNAMIC func1().DYNAMIC func2() // error |
Posted functions and events
Posted functions and events do not return a value to the calling
scripts. Therefore, you can only use POST for
the last function or event in a cascaded call. Calls before the
last must return a valid object that can be used by the following
call.
System events
System events can only be last in a cascaded list of calls,
because their return value is a long (or they
have no return value). They do not return an object that can be
used by the next call.
An event you have defined can have a return value whose datatype
is an object. You can include such events in a cascaded call.