how to make full jump with single press - actionscript-3

Question

This is a very simple question but even after googling i am not getting the right idea.
i have a hero who i want to make jump. i have written the code in my logic but the problem is i have to hold the key to perform the whole jump. lets say it will go y-= 20but if i hold my button its going the full distance. But if i click once its not going/ passing the full distance.
i want to make my hero jump the whole way with a single press, i mean just 1 press not holding down the button.
here is my code
import flash.display.Stage;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.display.MovieClip;
import flash.events.Event;
var grav:int = 0;
var floor = 450;
var jumping:Boolean = false;
stage.addEventListener(KeyboardEvent.KEY_DOWN , keyDownHandaler);
stage.addEventListener(KeyboardEvent.KEY_UP , KeyUpHandaler);
stage.addEventListener(Event.ENTER_FRAME , update);
function gravity ():void
{
hero.y += grav;
if (hero.y+hero.height/2 <floor){
grav++;
}
else {
grav = 0;
hero.y = floor - hero.height/2 ;
}
}
function keyDownHandaler(Devent:KeyboardEvent):void
{
if (Devent.keyCode == Keyboard.W)
{
jumping = true;
}
}
function KeyUpHandaler (Uevent:KeyboardEvent):void
{
if (Uevent.keyCode == Keyboard.W)
{
jumping = false;
}
}
function update(Levent:Event):void
{
if (jumping)
{
hero.y -= 20;
}
gravity();
}

Answer 1

I think the trick you need to work out is keeping the "jumping" flag set until the entire jump sequence is finished. Currently you have it resetting as soon as the button lifts up, then setting again when it's re-pressed.
There is actually no reason to turn off the jumping flag just because the user lifted the button.
Right here:
hero.y += grav;
if (hero.y+hero.height/2 <floor){
grav++;
}
You have a check to see if the character has hit the floor. It should be there that the jump sequence finishes.
All the stuff you do to your character should not be tracked on the KEY being DOWN. It should be tracked on the jumping=true. The key being pressed just starts the sequence. And you do need to keep that flag so as not to start the sequence again if it's already running.

Answer 2

Added because the first answer is already pretty long. This is an answer with the requested re-write of the OP's code: (Read notes at the end)
import flash.display.Stage;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.display.MovieClip;
import flash.events.Event;
var grav:double = 0.025; //Change this to make gravity stronger or weaker.
var gravInc:double = .2; //Changed to "double" because int is too large an increment. If double doesn't work, try float or decimal.
var floor = 450;
var jumping:Boolean = false;
stage.addEventListener(KeyboardEvent.KEY_DOWN , keyDownHandaler);
stage.addEventListener(KeyboardEvent.KEY_UP , KeyUpHandaler);
stage.addEventListener(Event.ENTER_FRAME , update);
function gravity ():void
{
if (hero.y+hero.height/2 < floor){
//grav++; //not needed
gravInc = gravInc - grav; //GravInc starts strong, and gradually decreases. It will eventully be less than zero, and start negetive.
hero.y -= gravInc; //The effect of which is the chracter will move upward until gravity takes over, and make hero move downward - increaseing speed until it hits the floor.
} else {
//grav = 0; Not needed
hero.y = floor - hero.height/2 ;
//We've hit the floor. Stop jump sequence
jumping = false;
}
}
function keyDownHandaler(Devent:KeyboardEvent):void
{
if (Devent.keyCode == Keyboard.W)
{
if (jumping==false) { //The character is not already jumping
//This initiates the jump sequence
//set up the jump sequence by resetting the gravInc and setting jumping to true
gravInc = .2;
jumping = true;
//Start the jump now so that the character is off the floor
hero.y -= gravInc;
}
}
}
function KeyUpHandaler (Uevent:KeyboardEvent):void
{
if (Uevent.keyCode == Keyboard.W)
{
// jumping = false;
// Not needed here
}
}
function update(Levent:Event):void
{
// This whole thing goes. It is not needed because the jumping==true will handle it.
// if (jumping)
// {
// hero.y -= 20;
// }
if ( jumping==true ){
gravity();
}
}
I have no way of testing this code. I commented out the parts of your code that were unnecessary, and I added in the things that you'd need to make it function.
ActionScript syntax is very similar to JavaScript. So I'm including this link as a sort-of demo to show how the whole gravity thing works in an actual program. Bounding balls
View the source on that page.
Hopefully this does the trick for you.