import fl.controls.CheckBox;
import fl.controls.TextInput;

var cB:CheckBox = new CheckBox();
cB.label = "Edit Text";
cB.addEventListener(Event.CHANGE, cB_edit);
cB.move(10, 5);
addChild(cB);

var tI:TextInput = new TextInput();
tI.editable = false;
tI.move(17, 30);
addChild(tI);

function cB_edit(evt:Event):void {
    tI.editable = cB.selected;
}