Application Techniques
Selected PowerScript Topics

Dot notation lets you qualify the item you are referring to instance variable, property, event, or function with the object that owns it.

Dot notation is for objects. You do not use dot notation for global variables and functions, because they are independent of any object. You do not use dot notation for shared variables either, because they belong to an object class, not an object instance.

Qualifying a reference

Dot notation names an object variable as a qualifier to the item you want to access:

objectvariable.item

The object variable name is a qualifier that identifies the owner of the property or other item.

Adding a parent qualifier

To fully identify an object, you can use additional dot qualifiers to name the parent of an object, and its parent, and so on:

parent.objectvariable.item

A parent object contains the child object. It is not an ancestor-descendant relationship. For example, a window is a control's parent. A Tab control is the parent of the tab pages it contains. A Menu object is the parent of the Menu objects that are the items on that menu.

Many parent levels

You can use parent qualifiers up to the level of the application. You typically need qualifiers only up to the window level.

For example, if you want to call the Retrieve function for a DataWindow control on a tab page, you might qualify the name like this:

w_choice.tab_alpha.tabpage_a.dw_names.Retrieve()

Menu objects often need several qualifiers. Suppose a window w_main has a menu object m_mymenu, and m_mymenu has a File menu with an Open item. You can trigger the Open item's Selected event like this:

w_main.m_mymenu.m_file.m_open.EVENT Selected()

As you can see, qualifying a name gets complex, particularly for menus and tab pages in a Tab control.

How many qualifiers?

You need to specify as many qualifiers as are required to identify the object, function, event, or property.

A parent object knows about the objects it contains. In a window script, you do not need to qualify the names of the window's controls. In scripts for the controls, you can also refer to other controls in the window without a qualifier.

For example, if the window w_main contains a DataWindow control dw_data and a CommandButton cb_close, a script for the CommandButton can refer to the DataWindow control without a qualifier:

dw_data.AcceptText()
dw_data.Update()

If a script in another window or a user object refers to the DataWindow control, the DataWindow control needs to be qualified with the window name:

w_main.dw_data.AcceptText()

Referencing objects

There are three ways to qualify an element of an object in the object's own scripts:

This pronoun

In a script for the object, you can use the pronoun This as a generic reference to the owning object:

This.property
This.function

Although the property or function could stand alone in a script without a qualifier, someone looking at the script might not recognize the property or function as belonging to an object. A script that uses This is still valid if you rename the object. The script can be reused with less editing.

You can also use This by itself as a reference to the current object. For example, suppose you want to pass a DataWindow control to a function in another user object:

uo_data.uf_retrieve(This)

This example in a script for a DataWindow control sets an instance variable of type DataWindow so that other functions know the most recently used DataWindow control:

idw_currentdw = This

Parent pronoun

The pronoun Parent refers to the parent of an object. When you use Parent and you rename the parent object or reuse the script in other contexts, it is still valid.

For example, in a DataWindow control script, suppose you want to call the Resize function for the window. The DataWindow control also has a Resize function, so you must qualify it:

// Two ways to call the window function
w_main.Resize(400, 400)
Parent.Resize(400, 400)

// Three ways to call the control's function
Resize(400, 400)
dw_data.Resize(400, 400)
This.Resize(400, 400)

GetParent function

The Parent pronoun works only within dot notation. If you want to get a reference to the parent of an object, use the GetParent function. You might want to get a reference to the parent of an object other than the one that owns the script, or you might want to save the reference in a variable:

window w_save
w_save = dw_data.GetParent()

For example, in another CommandButton's Clicked event script, suppose you wanted to pass a reference to the control's parent window to a function defined in a user object. Use GetParent in the function call:

uo_winmgmt.uf_resize(This.GetParent(), 400, 600)

ParentWindow property and function

Other tools for getting the parent of an object include:

For more about these pronouns and functions, see the section called “Pronouns” in PowerScript Reference and the section called “ParentWindow” in PowerScript Reference.

Objects in a container object

Dot notation also allows you to reach inside an object to the objects it contains. To refer to an object inside a container, use the Object property in the dot notation. The structure of the object in the container determines how many levels are accessible:

control.Object.objectname.property
control.Object.objectname.Object.qualifier.qualifier.property

Objects that you can access using the Object property are:

These expressions refer to properties of the DataWindow object inside a DataWindow control:

dw_data.Object.emp_lname.Border
dw_data.Object.nestedrpt[1].Object.salary.Border

No compiler checking

For objects inside the container, the compiler cannot be sure that the dot notation is valid. For example, the DataWindow object is not bound to the control and can be changed at any time. Therefore, the names and properties after the Object property are checked for validity during execution only. Incorrect references cause an execution error.

For more information

For more information about runtime checking, see Optimizing expressions for DataWindow and external objects.

For more information about dot notation for properties and data of DataWindow objects and handling errors, see DataWindow Reference.

For more information about OLE objects and dot notation for OLE automation, see Using OLE in an Application.