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
datatype The name of the datatype is the same as the name of the window.
For example, when you save a window named w_employee, PowerBuilder internally
creates a datatype named w_employee. - A new global variable of the new datatype 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:
Figure 6-1: Variable declaration
By duplicating the name of the datatype and variable, PowerBuilder allows new
users to access windows easily through their variables while ignoring
the concept of datatype.
What happens when you open a window
To open a window, you use the Open function,
such as:
|
1 |
Open(w_employee) |
This actually creates an instance of the datatype w_employee and
assigns 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.