About using variables
General information
To use or set a variable’s value in a PowerBuilder
script, you name the variable. The variable must be known to the
compiler—in other words, it must be in scope.
You can use a variable anywhere you need its value—for
example, as a function argument or in an assignment statement.
How PowerBuilder looks for variables
When PowerBuilder executes a script and finds an unqualified
reference to a variable, it searches for the variable in the following
order:
-
A local variable
-
A shared variable
-
A global variable
-
An instance variable
As soon as PowerBuilder finds a variable with the specified
name, it uses the variable’s value.
Referring to global variables
To refer to a global variable, you specify its name in a script.
However, if the global variable has the same name as a local or
shared variable, the local or shared variable will be found first.
To refer to a global variable that is masked by a local or
shared variable of the same name, use the global scope operator
(::) before the name:
|
1 |
::<span>globalname</span> |
For example, this statement compares the value of local and
global variables, both named total:
|
1 |
IF total < ::total THEN ... |
Referring to instance variables
You can refer to an instance variable in a script if there
is an instance of the object open in the application. Depending
on the situation, you might need to qualify the name of the instance
variable with the name of the object defining it.
Using unqualified names
You can refer to instance variables without qualifying them
with the object name in the following cases:
-
For application-level variables, in scripts for
the application object -
For window-level variables, in scripts for the window
itself and in scripts for controls in that window -
For user-object-level variables, in scripts for
the user object itself and in scripts for controls in that user
object -
For menu-level variables, in scripts for a menu
object, either the highest-level menu or scripts for the menu objects
included as items on the menu
For example, if w_emp has an
instance variable EmpID, then you can reference EmpID without
qualification in any script for w_emp or
its controls as follows:
|
1 |
sle_id.Text = EmpID |
Using qualified names
In all other cases, you need to qualify the name of the instance
variable with the name of the object using dot notation:
|
1 |
<span>object.instancevariable</span> |
This requirement applies only to Public instance variables.
You cannot reference Private instance variables outside the object
at all, qualified or not.
For example, to refer to the w_emp instance
variable EmpID from a script outside the window,
you need to qualify the variable with the window name:
|
1 |
sle_ID.Text = w_emp.EmpID |
There is another situation in which references must be qualified.
Suppose that w_emp has an instance
variable EmpID and that in w_emp there
is a CommandButton that declares a local variable EmpID in
its Clicked script. In that script, you must qualify all references
to the instance variable:
|
1 |
Parent.EmpID |
Using pronouns as name qualifiers
To avoid ambiguity when referring to variables, you might
decide to always use qualified names for object variables. Qualified
names leave no doubt about whether a variable is local, instance,
or shared.
To write generic code but still use qualified names, you can
use the pronouns This and Parent to
refer to objects. Pronouns keep a script general by allowing you
to refer to the object without naming it specifically.
Window variables in window scripts
In a window script, use the pronoun This to
qualify the name of a window instance variable. For example, if
a window has an instance variable called index,
then the following statements are equivalent in a script for that
window, as long as there is no local or global variable named index:
|
1 |
index = 5 |
|
1 |
This.index = 5 |
Window variables in control scripts
In a script for a control in a window, use the pronoun Parent to
qualify the name of a window instance variable—the window
is the parent of the control. In this example, the two statements
are equivalent in a script for a control in that window, as long
as there is no local or global variable named “index”:
|
1 |
index = 5 |
|
1 |
Parent.index = 5 |
Naming errors
If a local or global variable exists with the name “index,” then
the unqualified name refers to the local or global variable. It
is a programming error if you meant to refer to the object variable.
You get an informational message from the compiler if you use the
same name for instance and global variables.