Introduction to PowerBuilder

Cascaded Events and Functions

The event/function syntax allows you to make nested event/function calls. The return value of the first event/function must be an object and it becomes the object  upon which the second event/function acts.

// instance variables
// int ii_hours
// String ii_YarnType

NonVisualObject lnc_object
nc_MachineObject lnc_MachObj
Long li_Prod

lnc_MachObj = Create nc_MachineObject
lnc_object = lnc_MachObj.Function Trigger &
            Dynamic of_GetObject ( ii_no )

If NOT IsValid( lnc_object ) Then Return -100
li_Prod =.lnc_Object.Function Trigger Dynamic of_GetProd &
                 ( ii_hours, ii_YarnType )
If li_Prod = 0 Then
   // Error handling
End If
Destroy lnc_MachObj

The above example calculates production for different type of machines; machine from different  vendors and of different makes have different formulas for production calculation. Function call of_GetObject() at custom class object nc_MachineObject returns appropriate custom class object depending on the vendor and the make of the machine. The second function of_GetProd() returns production for that machine depending on the number of hours that machine ran and the type of the product.

// instance variables
// int ii_hours
// String ii_YarnType

nc_MachineObject lnc_MachObj
Long li_Prod

lnc_MachObj = Create nc_MachineObject
li_Prod = lnc_MachObj.Function Trigger Dynamic of_GetObject &
          ( ii_no ).of_GetProd( ii_hours, ii_YarnType )
If li_Prod = 0 Then
   // Error handling
End If
Destroy lnc_MachObj

The above code does the same thing as the earlier code listing, using nested function calls. As you can see here, you can't check if the returned object is a valid object or not. Make sure to check for valid objects and for error handling in the called objects.

If you use DYNAMIC keyword for the first event/function from left, it would apply for all nested event/function calls. Another suggestion would be that if you want to post event/function calls,  do it only at the last event/function call.

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