Flex基础！

Sky-Tiger

Both null and undefined conceptually represent the absence of data. The null value
represents the absence of data for variables, parameters, and return values with a
specified type annotation set to anything but Boolean, int, uint, and Number

Sky-Tiger

By contrast, the undefined value represents the absence of data for variables,
parameters, and return values without a specified type annotation

asangel

老虎是不是在赚积分，

asangel

太不厚道了

Sky-Tiger

If you define a custom component and you want to support the data property, your component must implement the mx.core.IDataRenderer interface. If your component is a subclass of a class that already implements the mx.core.IDataRenderer interface, you do not have to reimplement the interface.

To add programmatic logic to the controls in your item renderer or item editor that already implement the data property, you can override the setter or getter method for the data property. Typically, you override the setter method so that you can perform some operation based on the value that is passed to it.