Help with adding image onclick

Question

Hey everyone,
I am making a simple game in AS3 and need help with adding an image once they have click on something.
On the left of the screen are sentences and on the right an image of a form. When they click each sentence on the left, writing appears on the form. Its very simple. With this said, what I would like to do is once the user click one of the sentences on the left, I would like a checkmark image to appear over the sentence so they know they have already clicked on it.
How would I go about adding this to my code?
var fields:Array = new Array();
one_btn.addEventListener(MouseEvent.CLICK, onClick1a);
one_btn.buttonMode = true;
function onClick1a(event:MouseEvent):void
    fields.push(new one_form());
    fields[fields.length-1].x = 141;
    fields[fields.length-1].y = -85;
    this.addChild(fields[fields.length-1]);   
    one_btn.removeEventListener(MouseEvent.CLICK, onClick1a);
    one_btn.buttonMode = false;
    //gotoAndStop("one")
two_btn.addEventListener(MouseEvent.CLICK, onClick2a);
two_btn.buttonMode = true;
function onClick2a(event:MouseEvent):void
    fields.push(new two_form());
    fields[fields.length-1].x = 343.25;
    fields[fields.length-1].y = -85;
    this.addChild(fields[fields.length-1]);
    two_btn.removeEventListener(MouseEvent.CLICK, onClick2a);
    two_btn.buttonMode = false;
    //gotoAndStop("two")

Answer 1

I don't know where you're positioning the button that should enable/disable the checkbox but for "one_btn" let's just say it's at position: x=100, y=200. Say you'd want the checkbox to be to the left of it, so the checkbox would be displayed at: x=50, y=200. Also say you have a checkbox graphic in your library, exported for actionscript with the name "CheckBoxGraphic".
Using your code with some sprinkles:
// I'd turn this into a sprite but we'll use the default, MovieClip
var _checkBox:MovieClip = new CheckBoxGraphic();
// add to display list but hide
_checkBox.visible = false;
// just for optimization
_checkBox.mouseEnabled = false;
_checkBox.cacheAsBitmap = true;
// adding it early so make sure the forms loaded don't overlap the
// checkbox or it will cover it, otherwise swapping of depths is needed
addChild(_checkBox);
// I'll use a flag (a reference for this) to know what button is currently pushed
var _currentButton:Object;
one_btn.addEventListener(MouseEvent.CLICK, onClick1a);
one_btn.buttonMode = true;
function onClick1a(event:MouseEvent):void
     // Check if this button is currently the pressed button
     if (_currentButton == one_btn)
          // disable checkbox, remove form
          _checkBox.visible = false;
          // form should be last added to fields array, remove
          removeChild(fields[fields.length - 1]);
          fields.pop();
          // clear any reference to this button
          _currentButton = null;
     else
          // enable checkbox
          _checkBox.visible = true;
          _checkBox.x = 50;
          _checkBox.y = 200;
          // add form
          fields.push(new one_form());
          fields[fields.length-1].x = 141;
          fields[fields.length-1].y = -85;
          this.addChild(fields[fields.length-1]);
          // save this button as last clicked
          _currentButton = one_btn;
     // not sure what this is
    //gotoAndStop("one")
I'd also centralize all the click handlers into a single handler and use the buttons name to branch on what to do, but that's a different discussion. Just see if this makes sense to you.
The jist is a graphic of a checkbox that is a MovieClip symbol in your library exported to actionscript with the class name CheckBoxGraphic() is created and added to the display list.
I made a variable that points itself to the last clicked button, when the "on" state is desired. If I detect the last clicked button was this button, I remove the form I added and the checkbox. If the last clicked button is not this button, I enable and position the checkbox as well as add the form.
What is left to do is handle the sitation where multiple buttons are on the screen. When a new button is pushed it should remove anything the previous button added. This code simply demonstrates clicking the same button multiple times to toggle it "on and off".