How to do you get an character to jump?

Question

This is my fist time ever needing to use this for one of my games. I want to have the character jump. I have been trying to get this result for about an hour, but with no luck =( I am using AS3, and flash CS5.5. So far all my code does is make the character go left, and right based on keyboard input. Could someone please help?

Here is my code so far:

public class Dodgeball extends MovieClip
{
    public var character:Character;
    public var rightDown:Boolean = false;
    public var leftDown:Boolean = false;
    public var speed:Number = 3;
    public var timer:Timer;


    public function Dodgeball()
    {

        character= new Character();
        addChild(character);

        stage.addEventListener(KeyboardEvent.KEY_DOWN, myKeyDown);
        stage.addEventListener(KeyboardEvent.KEY_UP, MyKeyUp);
        timer = new Timer(24);
        timer.addEventListener(TimerEvent.TIMER, moveClip);
        timer.start();

    }
    public function myKeyDown(event:KeyboardEvent):void
    {
        if (event.keyCode == Keyboard.RIGHT)
        {
        rightDown = true;

            if(character.currentLabel != "walkingRight")
            {
                character.gotoAndStop ("walkingRight");
            }
        }
        if (event.keyCode == Keyboard.LEFT)
        {
            leftDown = true;
                if (character.currentLabel != "backingUp")
                {
                    character.gotoAndStop("backingUp");
                }
        }
    }
    public function MyKeyUp(event:KeyboardEvent):void
    {
        if(event.keyCode == Keyboard.RIGHT)
        {
            character.gotoAndStop("standing");
            rightDown = false;
        }
        if (event.keyCode == Keyboard.LEFT)
        {
            character.gotoAndStop("standingLeft");
            leftDown = false;
        }
    }
    public function moveClip(event:TimerEvent):void
    {
        if (rightDown)
        {
            character.x += speed;
        }
        if (leftDown)
        {
            character.x -=speed;
        }
        event.updateAfterEvent();
    }
}

}

Answer 1

A very simple approach is to have a vertical speed as well as a horizontal speed. When the user presses "UP" or "JUMP", set y speed to a negative value and update it in your movieClip function. When the character gets to a certain height, reverse the speed.

Using gravity and acceleration looks better but this is a really good place to start. Look into kinematic equations to see how you would make the character accelerate.

public var originalY;

public function myKeyDown(event:KeyboardEvent):void
{
    if (event.keyCode == Keyboard.UP && vSpeed == 0)
    {
        originalY = character.y;
        ySpeed = -1;
    }
}


public function moveClip(event:TimerEvent):void
{
    if (vSpeed != 0)
    {
        character.y += vSpeed;

        /* make the character fall down after reaching max jump height */
        if(originalY - character.y > jumpHeight) {
            vSpeed = vSpeed * -1;
        }

        /* level the character after he's hit the ground (so he doesn't go through) */
        else if(character.y >= originalY) {
            character.y = originalY;
            vSpeed = 0;
        }
    }
}

Answer 2

What I would do is create a motion tween of the character jumping. then call gotoAndPlay on that frame, and on the last frame of the tween put a stop, or a gotoAndStop on the "stationary" frame, or whatever frame represents a neutral position.

   if (event.keyCode == Keyboard.SHIFT)
   {
       character.gotoAndPlay("simpleJump");
       jumpDown = false;
   }

This will give you the greatest animation control over the look and feel. You could also do it programmatically, but personally, I recommend against it. It will take less time to set it up, and you can tweak and refine the jump animations later. You could make several types of jump animations based on object near the target etc.

I would also change this stuff:

if(character.currentLabel != "walkingRight")

By defining a new function where you have all the rules for when and where something can be done, so that in your control logic, you just call

if(characterCan(character,"walkright")) ...

Where characterCan(String) is a method that check if this is possible. For instance, if you are jumping and shooting, you obviously cannot walk right, so in the end, you will have to start adding pieces of logic into those if statements and it's gonna become a cluttered mess.

Answer 3

One method you can try is found here: http://www.actionscript.org/forums/showthread.php3?t=256009 Like your speed variable, grav determines the vertical position of the character.

var grav:Number = 10;
var jumping:Boolean = false;
var jumpPow:Number = 0;

stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDown);
stage.addEventListener(Event.ENTER_FRAME, update);

function onKeyDown(evt:KeyboardEvent):void
{
    if(evt.keyCode == Keyboard.UP)
    {
        if(jumping != true)
        {
            jumpPow = -50;
            jumping = true;
        }
    }   
}


function update(evt:Event):void
{
    if(jumping)
    {
        player_mc.y += jumpPow;
        jumpPow += grav;

        if(player_mc.y >= stage.stageHeight)
        {
            jumping = false;
            player_mc.y = stage.stageHeight;
        }
    }
}    

Edit: Jason's method is fine, but I'm not sure if it would be useful if you plan to have some kind of collision detection.