About window instances
When you build an application, you may want to display several
windows that are identical in structure but have different data
values.
For example, you may have a w_employee window and
want to display information for two or more employees at the same
time by opening multiple copies (instances) of the w_employee
window.
You can do that, but you need to understand how PowerBuilder stores
window definitions.
How PowerBuilder stores window definitions
When you save a window, PowerBuilder actually generates two
entities in the library:
- A new
data type The name of the data type is the same as the name of the window.
For example, when you save a window named w_employee, PowerBuilder internally
creates a data type named w_employee. - A new global variable of the new data
type The name of the global variable is the same as the name of
the window.
For example, when you save the w_employee window,
you are also implicitly defining a global variable named w_employee
of type w_employee.It is as if you had made the following declaration:
By duplicating the name of the data type and variable, new PowerBuilder users can
access windows easily through their variables while ignoring the
concept of data type.
What happens when you open a window
To open a window, you use the Open function, such as:
|
1 |
Open(w_employee) |
What this actually does is create an instance of the data
type w_employee and assign it a reference to the global
variable, also named w_employee.
As you have probably noticed, when you open a window that
is already open, PowerBuilder simply activates the existing window;
it does not open a new window. For example, consider this script
for a CommandButton’s Clicked event:
|
1 |
Open(w_employee) |
No matter how many times this button is clicked, there is
still only one window w_employee. It is pointed to by the
global variable w_employee.
To open multiple instances of a window, you declare variables
of the window’s type.