Declaring and Using Variables<A NAME=65> </A>

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## Declaring and Using Variables

The private variables of a widget class do not need to be declared. In fact they can be initialized and used anywhere by any method. Usually, however, general purpose private variables are initialized by the `InitWidgetRec` method and subwidget variables are initialized in the `ConstructWidget` method.

We have seen in the `tixArrowButton:InitWidgetRec` example that the private variable `data(count)` was initialized there. Also, the private variable `data(w:button)` was initialized in `tixArrowButton:ConstructWidget` and subsequently used in `tixArrowButton:SetBindings`.

In contrast, public variables must be declared inside the class declaration. The following arguments are used to declare the public variables and specify various options for them:

> - `-flag`: As shown in the class declaration in figure 6-2, the `-flag` argument declares all the public variables of the TixArrowButton class, `-direction` and `-state`

> - `-configspec`: We can use the `-configspec` argument to specify the details of each public variable. For example, the following declaration

>   > `-configspec {
>   > {-direction direction Direction e}
>   > {-state state State normal}
>   > }`

>   specifies that the `-direction` variable has the resource name `direction` and resource class `Direction`; its default value is `e`. The application programmer can assign value to this variable by using the `-direction` option in the command line or by specifying resources in the Tk option database with its resource name or class. The declaration of `-state` installs similar definitions for that variable.

> - `-alias`: The `-alias` argument is used to specify alternative names for public variables. In our example, the setting

>   > `-alias {
>   > {-dir -direction}
>   > }`

>   specifies that `-dir` is the same variable as `-direction`. Therefore, when the application issue the command

>   > `.up config -dir w`

>   it is the same as issuing

>   > `.up config -direction w`

>   The `-alias` option provides only an alternative name for the application programmer. Inside the widget's implementation code, the variable is still accessed as `data(-direction)`, not `data(-dir)`.

- Initialization of Public Variables
- Type Checker
- Public Variable Configuration Methods
- Configuration Methods and Public Variable Initialization