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:
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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.
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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: 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:
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:
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.
