Unity-实例化新对象时为空引用

Question

I'm trying to cycle through a 2D array of card objects and instantiate them in my Unity scene. However, I'm getting a Null reference exception when trying to instantiate them. Here is the code that instantiates the objects:

//Setting up initial board
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 4; j++){
            //Checked with debug.log, this should work Debug.Log (board[j, i].name);
            Debug.Log(board[j, i].name);
            temp = Instantiate(board[j,i]) as GameObject;
            CardScript cs = temp.GetComponent<CardScript>();
            objectBoard[j, i] = cs;
            //Setting locations of the cards
            objectBoard[j, i].transform.position = new Vector3(30 * j + 20, 50 * i +   70, 0);
        }
    }

The error occurs in the line 'CardScript cs = new.... I originally had the error in the temp = Instantiate... line, when the code was GameObject temp = Instantiate.... It fixed when I made temp a private GameObject variable in the code. I don't think I can do that with this one, because I need to have a reference to each individual object I'm instantiating.

Full Code:

public class MatchScript : MonoBehaviour {

public CardScript[] potentialCards;

private CardScript[,] board;
private CardScript[,] objectBoard;
private List<CardScript> entries;
private GameObject temp;


// Use this for initialization
void Start () {
    entries = new List<CardScript> ();
    objectBoard = new CardScript[4,3];
    board = new CardScript[4, 3];
    foreach (CardScript c in potentialCards)
        entries.Add (c);
    foreach (CardScript c in potentialCards)
        entries.Add (c);

    //Loading up the board
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 4; j++){
            int k = Random.Range(0, entries.Count);
            board[j, i] = entries[k];

            entries.RemoveAt(k);
        }
    }

    //Setting up initial board
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 4; j++){
            //Checked with debug.log, this should work Debug.Log (board[j, i].name);
            Debug.Log(board[j, i].name);
            temp = Instantiate(board[j,i]) as GameObject;
            CardScript cs = temp.GetComponent<CardScript>();
            objectBoard[j, i] = cs;
            //Setting locations of the cards
            objectBoard[j, i].transform.position = new Vector3(30 * j + 20, 50 * i + 70, 0);
        }
    }
}

// Update is called once per frame
void Update () {

}

Answer 1

I'm not really sure why this happen. But you can fix this by change

temp = Instantiate(board[j,i]) as GameObject;

to

temp = Instantiate(board[j,i].gameObject) as GameObject;

Answer 2

"expression as Type" clause returns expression cast to Type if and only if actual type of expression is derived from Type, otherwise it returns null.

Instantiate makes an independent copy of an object passed, which, naturally, has type CardScript. Now, there is some possible misunderstanding: GameObject is a base class for all "entities in Unity scenes", but that doesn't include all classes you create on your own. If CardScript is a class you created and it doesn't inherit any class explicitly, then it inherits System.Object (which is base class for all C# classes).

If CardScript is derived from GameObject, then you should probably provide that class as well.