How to make a character touch the ground in Unity 2D?

Question

Unity

I'm making an android game using Unity 2D. I have character jump code:

public void Jump(bool isJump)
    {
        isJump = groundCheck;

        if (groundCheck)
        {
            rb2d.velocity = new Vector2(rb2d.velocity.x, jumpPower);
        }

    }

I tried to check if the character is on the ground in this way:

void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.tag == "ground")
        {
           groundCheck = true;
       }
    }

But that jump doesn't work at all. How do I make it so that the character can only jump if he is standing on the ground.
I'm new to C# programming. Please help me.

Answer 1

It does not work, most likely, because initially the variable groundCheckis equal falsein the declaration, you need to set it immediately true, because initially the character is already on the ground: And after the jump, immediately change to :
bool groundCheck = true;

if (groundCheck)
        {
            rb2d.velocity = new Vector2(rb2d.velocity.x, jumpPower);
            groundCheck = false;
        }