(Big unity noob here) I can jump while in the air, and I can't jump while moving on the x-axis - unity3d

Question

Have tried a few things but they didn't seem to work, so I was hoping that you guys could help me.
I've trying to make this demo for a little time now, but I can't seem to get the jumping to work.
When I try to jump while running, I can't. But I can however jump forever when i get up in the air, which is something that I would like to remove from the game.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class movement : MonoBehaviour
{
Rigidbody2D rb2d;
public float moveVelocity = 8f;
public float jumpVelocity = 15f;
public float fallMultiplier = 2.5f;
public float lowJumpMultiplier = 2f;
public const string RIGHT = "right";
public const string LEFT = "left";
public const string UP = "up";
string buttonPressed;
void Start()
{
rb2d = GetComponent<Rigidbody2D>();
}
void Update()
{
if (rb2d.velocity.y < 0)
{
rb2d.velocity += Vector2.up * Physics2D.gravity.y * (fallMultiplier - 1) *
Time.deltaTime;
}
else if (rb2d.velocity.y > 0 && !Input.GetButton ("Jump"))
{
rb2d.velocity += Vector2.up * Physics2D.gravity.y * (lowJumpMultiplier - 1) *
Time.deltaTime;
}
if (Input.GetKey(KeyCode.RightArrow))
{
buttonPressed = RIGHT;
}
else if (Input.GetKey(KeyCode.LeftArrow))
{
buttonPressed = LEFT;
}
else if (Input.GetKey(KeyCode.UpArrow))
{
buttonPressed = UP;
}
else
{
buttonPressed = null;
}
}
private void FixedUpdate()
{
if (buttonPressed == RIGHT)
{
rb2d.velocity = new Vector2(moveVelocity, rb2d.velocity.y);
}
else if (buttonPressed == LEFT)
{
rb2d.velocity = new Vector2(-moveVelocity, rb2d.velocity.y);
}
else if (buttonPressed == UP)
{
rb2d.velocity = Vector2.up * jumpVelocity;
}
else
{
rb2d.velocity = new Vector2(0, rb2d.velocity.y);
}
}
}

Answer 1

I am not sure why you are trying to control the gravity of the player when gravity is already applied to any gameObject with the RigidBody or RigidBody2D component attached to it. It is good that you are reading input in the Update() function and applying the motion inside of the FixedUpdate(). Here is a slight tweak to your current code, let me know how this goes.
Rigidbody2D rb2d;
public float moveVelocity = 8f;
public float jumpVelocity = 15f;
private float horizontalInput = 0.0f;
// did the player just try to jump
private bool justJumped = false;
void Start()
{
rb2d = GetComponent<Rigidbody2D>();
}
void Update()
{
// grab how the player is moving - this value is mapped to your arrow keys
// so horizontal is left / right arrow and Vertical is up/down arrow
// the value is between [-1, 1] respectively
horizontalInput = Input.GetAxis("Horizontal");
// player tried to jump, we are not currently jumping and the player is grounded
if(IsGrounded() && Input.GetKeyDown(KeyCode.UpArrow))
{
justJumped = true;
}
}
private void FixedUpdate()
{
// handle our jump
if(justJumped)
{
// we just applied a jump so do not apply it again
justJumped = false;
// you can either apply the jump by setting velocity, but I would recommend using AddForce instead
rb2d.AddForce(Vector2.up * jumpVelocity);
}
// we are moving in either the left or right direction
if(horizontalInput != 0)
{
// move in the horizontal axis, but keep our Y component of velocity the same in case we jumped
rb2d.velocity = new Vector2 (horizontalInput * moveVelocity, rigidBody.velocity.y);
}
else
{
// just in case we are not moving, assure this by setting the horizontal component of velocity to 0
rb2d.velocity = new Vector2 (0f, rigidBody.velocity.y);
}
}
// determines if this object is currently touching another object that is marked as ground
private bool IsGrounded() {
// our current position (the player)
Vector2 position = transform.position;
// the direction we are going to aim the raycast (down as that is where the ground is)
Vector2 direction = Vector2.down;
// the ground should be close, so check it very close to the player
float distance = 1.0f;
// check if we hit anything that is on the layer of just ground - ignore all other layers
// IMPORTANT:: Make sure to make a Layer and set all of your ground to this layer
RaycastHit2D hit = Physics2D.Raycast(position, direction, distance, LayerMask.GetMask("GroundLayer"));
// we hit a ground collider, so we are grounded
if (hit.collider != null) {
return true;
}
return false;
}
Let me know if this works for you. I changed a few things around such as using GetAxis() instead of using the arrow keys as in Unity, these are the same. I also changed your jump to use an AddForce2D instead of setting velocity. The one addition was I added a IsGrounded() which will detect if whatever object this script is on (I assume it is on your player object) is near or touching objects below them that are marked as GroundLayer. If you have questions comment below.