如何在一段时间内更改变量

Question

How to change a variable in Unity3D just for 5 seconds or until a certain event? For example, changing velocity:

void Start ()
{
    GetComponent<Rigidbody2D> ().velocity = Vector3.zero;
}

void Update ()
{
   if (Input.GetKey(KeyCode.W))
   {
       goUp ();
   }
}
public void goUp() {
   GetComponent<Rigidbody2D> ().velocity = new Vector2 (0, 10);
}

Since A is pressed, object goes up all the time. How to make object go up not all the time, but every frame while A is pressed? And when A is not pressed, object's velocity goes back to zero. I used to make it this way:

void Start () {
   GetComponent<Rigidbody2D> ().velocity = Vector3.zero;
}

void Update () {

   GetComponent<Rigidbody2D> ().velocity = Vector3.zero;

   if (Input.GetKey(KeyCode.A)) {
       goUp ();
   }

}

public void goUp() {
   GetComponent<Rigidbody2D> ().velocity = new Vector2 (0, 10);
}

But this method is not rational and overloads CPU. Also, I can't use Input.GetKeyUp(KeyCode.A) or "else" statement as a trigger.

Answer 1

I would use x as a property like if it was speed. I'll just psudeo code it.. On your Update() for each frame you only care about Speed in this case so you just call it. You don't have to constantly check for other values because those should be handled by other events.

Property Speed get;set;

    Void APressed()
{
     Speed = 5;
}

Void AReleased()
{
     Speed = 0;
}

Sorry I forgot the second part after 5 seconds.. You could add in something like this, If Unity supports the async keyword.. You would then update your A pressed to look like this

   Void APressed()
    {
         Speed = 5;
ReduceSpeedAfter5Seconds();
    }


public async Task ReduceSpeedAfter5Seconds()
{
    await Task.Delay(5000);
    Speed = 0;
}

Answer 2

have you tried this?

if (Input.GetKey(KeyCode.A)) {
       goUp ();
   }
else
{
    GetComponent<Rigidbody2D> ().velocity = Vector3.zero;
}

Answer 3

Take a look at CoRoutines in Unity/C#: http://docs.unity3d.com/Manual/Coroutines.html

This may do exactly what you need. I have put some pseudo code below if I understand your issue correctly.

if (Input.GetKeyDown("a")) {
    goUp();
    StartCoroutine("ReduceSpeedAfter5Seconds");
}

IEnumerator ReduceSpeedAfter5Seconds() {
GetComponent<Rigidbody2D> ().velocity = new Vector2 (0, 10);
        yield return new WaitForSeconds(5.0f);
}