Flash CS3 Documentation

Using ActionScript 2.0 Components > Creating Components > Creating the ActionScript class file > About core functions > About the constructor function

About the constructor function

You can recognize a constructor function because it has the same name as the component class. For example, the following code shows the ScrollBar component's constructor function:

function ScrollBar() {
}

In this case, when a new scroll bar is instantiated, the ScrollBar() constructor is called.

Generally, component constructors should be empty. Setting properties in constructors can sometimes lead to overwriting default values, depending on the order of initialization calls.

If your component extends UIComponent or UIObject, Flash automatically calls init(), createChildren(), and size() methods and you can leave your constructor function empty, as shown here:

class MyComponent extends UIComponent{
    ...
    // this is the constructor function
    function MyComponent(){
    }
}

All version 2 components should define an init() function that is called after the constructor has been called. You should place the initialization code in the component's init() function. For more information, see Defining the init() method.

If your component extends MovieClip, you may want to call an init() method, a createChildren() method, and a method that lays out your component from the constructor function, as shown in the following code example:

class MyComponent extends MovieClip{
    ...
    function MyComponent(){
        init()
    }

    function init():Void{
        createChildren();
        layout();
  }
    ...
}

For more information about constructors, see Writing the constructor function in Learning ActionScript 2.0 in Adobe Flash.

Flash CS3