I am writing a class that extends mx.core.UIComponent. In the constructor of this class, I would like to add a Button (spark.components.Button). However, creating a new Button object (such as var b:Button = new Button();) and then doing this.addChild(b) doesn't work -- no button is appearing. Is there any reason why a Button object can't be added as a child?
Edit: Just to add, when I print out the children, it says that the Button object is a child, but the Button doesn't show up.
Using UIComponent directly, you aren't getting the layout of the child handled for you; you would need to set the position and size of your child components manually (see docs).
Consider using a Group (or Canvas, if you're still on MX components) to handle child layout. You can still add rendering in updateDisplayList, just make sure you call super.updateDisplayList() as well.
You need to add the button in the createChildren method not in the constructor.
protected var button:Button;
override protected function createChildren():void {
super.createChildren();
button = new Button();
addChild(button);
}
Depending on what you are trying to do you may also need to implement the measure and updateDisplayList methods.
You need to read up on the differences between ActionScript components and Flex components. When using a Flex component, you must use container.addElement( element ), not container.addChild( child ). As far as I am aware, the only classes with this functionality descend from Group (at least in the Spark framework, the one I am most familiar with). So extending UIComponent will not allow you to add a Button, although a UIComponent can be added to a Flex container (which I do not believe a normal Sprite can do)
