Question

In ActionScript3, I am trying to access the properties of the caller object from a composite.

public class Robot {
 ...
 private var controlPanel:ControlPanel;
 ...
 public function Robot() {
 ...
 cPanel = new ControlPanel();
 ...
  }
 }

My ControlPanel needs to access properties from Robot instance, but I don’t think I can pass this when calling the ControlPanel…

public class ControlPanel{
...
 public function ControlPanel() {
  //How can I refer back to robot properties ?
  //
 }

}

I believe I am in the case of composition as a Robot has a ControlPanel. I am thinking of using events, but there are many properties I need to access.

What would be the best way to solve this?

Answer 1

You can always just let ControlPanel store a reference to its own Robot object, like so:

// ControlPanel
private var robot:Robot;

public function ControlPanel(robot:Robot) {
    this.robot = robot;
}

And then, when creating the control panel:

// Robot
public function Robot() {
    controlPanel = new ControlPanel(this);
}

Alternatively, you could create an even system of sorts, and then let the control panel dispatch them. You could create your own ControlPanelEvent class, and then let the Robot itself handle the results. For example, let’s say you change a property called foo in the control panel. You could dispatch it like this:

var event:ControlPanelEvent = new ControlPanelEvent(ControlPanelEvent.PROPERTY_CHANGE, "foo", value);

Then you’d receive it like this:

public function Robot() {
    controlPanel = new ControlPanel();
    controlPanel.addEventListener(ControlPanelEvent.PROPERTY_CHANGE, updateProperty);
}

public function updateProperty(event:ControlPanelEvent):void {
    if (event.key == "foo") {
        this.foo = event.value;
    }
}

However, that’s wordy and unnecessary. You could also use ActionScript’s array access notation in the event handler, which would be a simple one-liner:

this[event.key] = event.value;

Still, that’s not entirely secure, since you might not want the control panel to be able to update all of a robot’s properties. Instead, you could maintain a simple map of configurable properties that the robot can have, and update that instead:

private var configuration:Dictionary = new Dictionary();

public function Robot() {
    // ...
    configuration.foo = "bar";
    configuration.baz = "qux";
    //...
}

public function updateProperty(event:ControlPanelEvent):void {
    if (configuration.hasOwnProperty(event.key))
        configuration[event.key] = event.value;
}

There you go. Of course, you could always just store the configuration map in the ControlPanel itself, and let the Robot pull from that, but if you absolutely need it as a property of the robot, here are a few solutions.