Error #1063: Argument count mismatch - AS3 - actionscript-3

Question

I have a very simple animation i want to make but am stuck with these errors
ArgumentError: Error #1063: Argument count mismatch on ReverseCirculation_Complete_Graham_1_ActionScript3_fla::MainTimeline/Play(). Expected 0, got 1.
The idea is an animation will be paused, then clicked on "play" button to start with the ability to stop or pause the animation before clicking "Next" to preview the continued animation.
My code looks like this:
//imports needed
stop();
import flash.display.MovieClip;
import flash.events.MouseEvent;
import flash.events.Event;
import flash.display.Stage;
Play_btn.addEventListener(MouseEvent.CLICK,Play);
Stop_btn.addEventListener(MouseEvent.CLICK,Stop);
Next_btn.addEventListener(MouseEvent.CLICK,Next);
function Play()
{
blue1_mc.play();
red_mc.play();
green_mc.play();
}
function Stop()
{
blue1_mc.stop();
red_mc.stop();
green_mc.stop();
}
function Next(event:MouseEvent):void
{
gotoAndStop(2);
}
Many thanks
Graham

Answer 1

In AS3, when you define a function like so:
function Play()
You are telling it that there are no parameters/arguments for this function. Unlike similar ECMAScript based languages such as JavaScript, if you end up passing a parameter - for example doing Play("Hello") - it will throw an error.
When you setup a event handler, like you do here:
Play_btn.addEventListener(MouseEvent.CLICK,Play);
That event when triggered calls the function specified - Play - and passes it a MouseEvent object that describes the event (such as the object clicked, the mouse position etc.)
Since you've define the Play function to accept no arguments, you get the error saying there's an unexpected argument. (same for the Stop function).
To remedy the issue, you can do 1 of these two things:
Add a MouseEvent argument to the function:
function Play(event:MouseEvent){
Add a MouseEvent argument, but make it optional:
function Play(event:MouseEvent = null){
The second option, means that you can still simply call Play() without passing it an argument.