Using window arrays – PB Docs 70

Using window arrays

To create an array of windows, declare an array of the data
type of the window. For example, the following
statement declares an array named myarray, which contains five instances
of the window w_employee:

You can also create unbounded arrays of windows if the number
of windows to be opened is not known at compile time.

Opening an instance using an array

To open an instance of a window in an array, use the Open
function and pass it the array index. Continuing the example above,
the following statements open the first and second instances of
the window w_employee:

note.gif Moving first instance opened The statements in this example open the second instance of
the window at the same screen location as the first instance. Therefore,
you would want to call the Move function in the script to relocate
the first instance before the second Open function call.

Manipulating arrays

Using arrays of windows, you can manipulate particular instances
by using the array index. For example, the following statement hides
the second window in the array:

You can also reference controls in windows by using the array
index, such as:

note.gif Opening many windows When you open or close a large number of instances of a window,
you may want to use a FOR…NEXT control structure in the main window
to open or close the instances. For example:

Creating mixed arrays

In the previous example, all windows in the array are the
same type. You can also create arrays of mixed type. Before you
understand this technique, you need to know one more thing about
window inheritance: all windows you define are actually descendants
of the built-in data type window.

Suppose you have a window w_employee that is defined
from scratch, and w_customer that inherits from w_employee.
The complete inheritance hierarchy is the following:

mgwin02.gif

The system-defined object named window is the ancestor of
all windows you define in PowerBuilder. The built-in object named
window defines properties that are used in all windows (such as
X, Y, and Title).

If you declare a variable of type window, you can reference
any type of window in the application. This is because all user-defined
windows are a kind of window.

The following code creates an array of three windows. The
array is named newarray. The array can reference any type of window,
because all user-defined windows are derived from the window data
type:

The code uses this form of the Open function:

where windowVariable
is a variable of
type window (or a descendant of window) and windowType
is
a string that specifies the type of window.

The code above opens three windows: an instance of w_employee,
an instance of w_customer, and an instance of w_sales.

Using arrays versus using reference variables

When do you use reference variables and when do you use arrays
to manipulate window instances?

Item Advantages Disadvantages
Arrays You can refer to particular instances Arrays are more difficult to use. For
example, if the user closes the second window in an array, then
wants to open a new window, your code must determine whether to
add a window to the end of the array (thereby using more memory
than needed) or find an empty slot in the existing array for the
new window
Reference variables Easy to use–PowerBuilder manages them
automatically
You cannot manipulate particular instances
of windows created using reference variables

Suppose you use w_employee to provide or modify data
for individual employees. You may want to prevent a second instance
of w_employee opening for the same employee, or to determine
for which employees an instance of w_employee is open.
To do this kind of management, you must use an array. If you don’t
need to manage specific window instances, use reference variables
instead to take advantage of their ease of use.


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