How to Create a Flash MX Component - Page 14

_targetInstanceName: Creating Components that Change the Behavior of Other Stage Elements

We have taught you how to create a self-contained component, but one of the most exciting features introduced with Flash MX Components is the ability to create a component that modifies the behavior of some other stage element onto which it is dropped. For those of you who are familiar with Director, you will already know these as 'behaviors.'

With this feature, you can drag the component onto some other stage element (e.g., a movie clip or text field) and have the component alter that stage element's properties. For example, the scroll bar component that Macromedia provides places and sizes itself to any text field onto which it is dropped, and automatically provides scroll bar functionality to that text field. The _targetInstanceName property tells the component the name (String) of the stage element onto which it has been dropped. To access the target object's properties or methods, you use the following syntax from within a component method: this._parent[_targetInstanceName]. For example, to retrieve the width of the target object, you would write

this._parent[_targetInstanceName]._width

To make this property available, you include it in the list of your component parameters (see Figure above). You also get a special surprise: your component will 'snap' into place. When you drop your component over another stage element, your component will align itself with the upper left-hand corner of the target stage element. This is also a convenient visual check that the component has been connected with a target object. Alternatively, you can type in the name of the target object into the property inspector. If the component is not dropped onto a stage element, the _targetInstanceName property is set to the default value you give it when you add the property to the component's property list.