Move Character Tile by Tile - unity3d

Question

I am making a 2D game. I got a character and some tiles. The tiles are 1 x 1 unit, and placed in scene.
I used the following codes to move my character. Here is my character ("Hero")'s code:
public class Hero : MonoBehaviour {
private Vector2 speedX = new Vector2(1, 0);
private Vector2 speedY = new Vector2(0, 1);
void Update () {
if(Input.GetKey("left")) {
rigidbody2D.MovePosition(rigidbody2D.position - speedX * Time.deltaTime);
} else if(Input.GetKey("right")) {
rigidbody2D.MovePosition(rigidbody2D.position + speedX * Time.deltaTime);
} else if(Input.GetKey("up")) {
rigidbody2D.MovePosition(rigidbody2D.position + speedY * Time.deltaTime);
} else if(Input.GetKey("down")) {
rigidbody2D.MovePosition(rigidbody2D.position - speedY * Time.deltaTime);
}
}
}
It works, but it does not move as expected. It moves around 0.2 units when I press the arrow key once. How can I make the player moves 1 unit per key down ?
What did I miss?
Documentation: Rigidbody2D.MovePosition

Answer 1

From what I see, it looks like you want to achieve instant movement of character to new position once key is pressed. If so, you have two errors here:
You don't need to multiply speed (speedX or speedY) by Time.deltaTime.
Input.GetKey is not what you want to use, because it will return true in every frame where key is pressed (not once per key pressing). Instead, you need to use Input.GetKeyDown.
So, your code should look like this:
public class Hero : MonoBehaviour {
private Vector2 speedX = new Vector2(1, 0);
private Vector2 speedY = new Vector2(0, 1);
void Update () {
if(Input.GetKeyDown("left")) {
rigidbody2D.MovePosition(rigidbody2D.position - speedX);
} else if(Input.GetKeyDown("right")) {
rigidbody2D.MovePosition(rigidbody2D.position + speedX);
} else if(Input.GetKeyDown("up")) {
rigidbody2D.MovePosition(rigidbody2D.position + speedY);
} else if(Input.GetKeyDown("down")) {
rigidbody2D.MovePosition(rigidbody2D.position - speedY);
}
}
}