Communicating between a window and a user object

Sometimes you might need to exchange information between a window and a visual user object in the window. Consider these situations:

You have a set of buttons in a custom user object. Each of the buttons acts upon a file that is listed in a SingleLineEdit control in the window (but not in the user object).

You need to pass the contents of the SingleLineEdit control from the window to the user object.
You have a user object color toolbar. When the user clicks one of the colors in the user object, a control in the window changes to that color.

You need to pass the color from the user object to the window control.

This section discusses two techniques for handling this communication and presents a simple example.

**Table 14-4: Techniques for communicating information in a window**
Technique	Advantages	Disadvantages
Functions	Easy to use Supports parameters and return types, so is not prone to errors Supports data encapsulation and information hiding Best for complex operations	Creates overhead, might be unnecessary for simple operations
User events	Very flexible and powerful	Uses no type checking, so is prone to error

Communication with both techniques can be either synchronous (using Send for functions and the EVENT keyword for events) or asynchronous (using Post for functions and the POST keyword for events).

Directly referencing properties

Instead of using functions or user events, it is possible to directly reference properties of a user object. If you have a user object control, uo_1, associated with a custom user object that has a SingleLineEdit, sle_1, you can use the following in a script for the window:

uo_1.sle_1.Text = "new text"

However, it is better to communicate with user objects through functions and user events, as described below, in order to maintain a clean interface between the user object and the rest of your application.

The functions technique

Exchanging information using functions is straightforward. After a user object calls a function, any return value is available to any control within that object.

For how to use this technique, see “Example 1: using functions”.

To pass information from a window to a user object:

Define a public, user-object-level function that takes as arguments the information needed from the window.
Place the user object in the window.
When appropriate, call the function from a script in the window, passing the needed information as arguments.

To pass information from a user object to a window:

Define a public, window-level function that takes as parameters the information needed from the user object.
Place the user object in the window.
When appropriate, call the function from a script in the user object, passing the needed information as parameters.

The user events technique

You can define user-defined events, also called user events, to communicate between a window and a user object. You can declare user events for any PocketBuilder object or control.

A custom visual user object often requires a user event. After you place a custom visual user object in a window or in another custom user object, you can write scripts for events that occur only in the user object itself. You cannot write scripts for events in the controls in the user object.

You can, however, define user events for the user object, and trigger those events in scripts for the controls contained in that user object. In the Window painter, you write scripts for the user events, referencing components of the window as needed.

For more information about user events, see Chapter 8, “Working with User Events.” For instructions for using this technique, see “Example 2: using user events”.

To define and trigger a user event in a visual user object:

In the User Object painter, select the user object.

Make sure no control in the user object is selected.
In the Event List view, select Add from the pop-up menu.
In the Prototype window that displays, define the user event.

For how to do so, see “Defining user events”.
Use the Event keyword in scripts for a control to trigger the user event in the user object:
```
userobject.Event eventname ( )
```
For example, the following statement in the Clicked event of a CommandButton contained in a custom visual user object triggers the Max_requested event in the user object:
```
Parent.Event Max_requested()
```
This statement uses the pronoun Parent, referring to the custom visual user object itself, to trigger the Max_requested event in that user object.
Implement these user events in the Window painter.

To implement the user event in the window:

Open the window.
In the Window painter, select Insert>Control from the menu bar and place the custom visual user object in the window.
Double-click the user object, and then in the Script view, write scripts for the user events you defined in the User Object painter.