Unity 2D Platformer Jumping Issue - unity3d

Question

I'm able to get my sprite to jump using a Axis.RawInput. This input also serves as a parameter to trigger the jumping animation when the RawInput is greater than 0. This issue with this is when you release the key, the sprite instantly falls back down. How can I perform a fixed jump when the key is pressed once or held down and then have the sprite fall at a fixed rate while also having the animations trigger?
This is what I have in my PlayerMover script now.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class PlayerMover : MonoBehaviour
{
public Animator anim;
public Vector3 velocity = Vector3.zero;
public float runSpeed = 0f;
public float jumpSpeed = 0f;
private SpriteRenderer sp;
public float maxJump = 4f;
private void Awake()
{
sp = GetComponent<SpriteRenderer>();
}
void Update()
{
runSpeed = Input.GetAxisRaw("Horizontal");
jumpSpeed = Input.GetAxisRaw("Vertical");
anim.SetFloat("Jump", jumpSpeed);
anim.SetFloat("Speed", Mathf.Abs(runSpeed));
}
private void FixedUpdate()
{
Move(runSpeed, jumpSpeed*4);
}
void Move(float horizontal, float vertical)
{
if(horizontal > 0 || horizontal > 0 && vertical >0)
{
anim.SetBool("Idle", false);
sp.flipX = false;
}
else if(horizontal < 0 || horizontal <0 && vertical >0)
{
anim.SetBool("Idle", false);
sp.flipX = true;
}
else
anim.SetBool("Idle", true);
velocity.x = horizontal;
velocity.y = vertical;
transform.position += velocity * Time.fixedDeltaTime;
}
}
I've read about using something like
if(Input.GetKeyDown(GetKeyCode("Space"){
rigidbody2D.AddForce(new Vector2(0, 10), ForceMode2D.Impulse);
}
In order to move but it allows additional jumps whenever Space is pressed.

Answer 1

If you want to use something like:
if(Input.GetKeyDown(GetKeyCode("Space"))){
rigidbody2D.AddForce(new Vector2(0, 10), ForceMode2D.Impulse);
}
but need to stop the player from jumping when they're already in the air, just only allow them to do this when they're already on the floor. So:
if(Input.GetKeyDown(GetKeyCode("Space")) && isOnFloor()){
rigidbody2D.AddForce(new Vector2(0, 10), ForceMode2D.Impulse);
}
Where isOnFloor() is some function that checks if your character is on the floor. Depending on your game implementation this could be done several ways, but the most common one is to check if the player character is colliding with anything, and if so, if that collision object is below them. This stackexchange thread gives some code samples for how to achieve this.

Answer 2

In order to use this
if (Input.GetKeyDown(GetKeyCode("Space"))
{
rigidbody2D.AddForce(new Vector2(0, 10), ForceMode2D.Impulse);
}
you need to check if your player is colliding with the ground, so instead you would have a bool like bool isGrounded to check if you are touching the ground, to do this you can do it in the OnCollisionStay() to confirm it is true when you are colliding with the ground. You can use tags to check if the collider you are colliding with is the ground. Then when you jump, you need to say isGrounded = false; then it will not be true untill you land on the ground again
if (Input.GetKeyDown(GetKeyCode("Space") && isGrounded == true)
{
rigidbody2D.AddForce(new Vector2(0, 10), ForceMode2D.Impulse);
isGrounded = false;
}