Player won't jump in unity2d - unity3d

Question

here's my jump code it updates in void Update
void Jump()
{
if(isgrounded == true)
{
amountofjumps = jumps;
}
if(Input.GetKeyDown(KeyCode.UpArrow) && amountofjumps > 0)
{
rb2d.velocity = Vector2.up * jump * Time.deltaTime;
amountofjumps--;
}
else if(Input.GetKeyDown(KeyCode.UpArrow) && amountofjumps == 0 && isgrounded == true)
{
rb2d.velocity = Vector2.up * jump * Time.deltaTime;
}
}
here are the variables I use for my jump code
bool isgrounded;
public float groundcheckradius;
public LayerMask whatisground;
public float jump;
private int amountofjumps;
public int jumps;
here's how I detect the ground
void checkforground()
{
isgrounded = Physics2D.Raycast(transform.position,Vector2.down, groundcheckradius,whatisground);
}
void OnDrawGizmos()
{
Gizmos.color = Color.red;
Gizmos.DrawLine(transform.position, transform.position + Vector3.down * groundcheckradius);
}
thanks in advance

Answer 1

Velocity is often used for moving object try rigidbody2d.AddForce() instead.
void Jump()
{
if (isgrounded == true)
{
amountofjumps = jumps;
}
if (Input.GetKeyDown(KeyCode.UpArrow) && amountofjumps > 0 && isgrounded == true)
{
rb2d.AddForce(transform.up * jump, ForceMode2D.Impulse);
amountofjumps--;
}
}

Answer 2

First of all Time.deltaTime makes no sense when setting a velocity. A velocity already is frame-rate independent so when you multiply a velocity by Time.deltaTime (about 0.017 for 60 fps) it becomes extremely small/slow.
Secondly currently you overwrite the entire velocity so if your player is moving forward it will completely stop any movement on the X axis.
And finally when you are grounded you want always be able to jump ... not only if amountofjumps == 0 which will never be the case since right before you have set it to amountofjumps = jumps;! You don't want to check the amountofjumps at all when jumping from the ground!
You would probably rather use e.g.
// get the current velocoty of the rigidbody
var velocity = rb2d.velocity;
// Only overwrite the Y velocity with the jump
velocity.y = jump;
// re-assign the changed vector to the rgidbody
rb2d.velocity = velocity;
And then I would change the logic to something like e.g.
private void Jump()
{
if(isgrounded)
{
amountofjumps = jumps;
// when you are grounded you can always jump!
// Not only when the amountofjumps == 0
// actually when you are grounded the amountofjumps shouldn't matter at all
if(Input.GetKeyDown(KeyCode.UpArrow))
{
DoJump();
}
}
// As before while not grounded the amountofjumps is taken into account
else if(amountofjumps > 0)
{
if(Input.GetKeyDown(KeyCode.UpArrow))
{
DoJump();
}
}
}
private void DoJump()
{
// get the current velocoty of the rigidbody
var velocity = rb2d.velocity;
// Only overwrite the Y velocity with the jump
velocity.y = jump;
// re-assign the changed vector to the rgidbody
rb2d.velocity = velocity;
// Always reduce the amount of jumps also when jumping from the ground
amountofjumps--;
}