在foreach循环中为对象分配值

Posted 2021-04-12

using System;

namespace WorkingWithClasses
{
    class Program
    {
        static void Main(string[] args)
        {
            //create 5 player objects
            Player[] players = new Player[5];

            //assigning a value to a player brings exception error:
            foreach(Player player in players)
            {
                player.Skill = 5;
            }


            float skillSum = 0;
            foreach(Player player in players)
            {
                skillSum += player.Skill;
            }

            Console.WriteLine(skillSum);
        }
    }
    class Player
    {
        public float Skill { get; set; }
    }
}

答案

播放器数组中的每个“玩家”都没有初始化。尝试使用此for循环而不是要获取空引用的foreach循环：

for (var i = 0; i < players.Length; i++)
{
    players[i] = new Player() { Skill = 5 };
}

您也可以使用它，但是它比使用for循环遍历数组要慢：

using System.Linq;

players = Enumerable.Repeat(new Player() { Skill = 5 }, 5).ToArray();

另一答案

您尚未初始化播放器类，请尝试以下以获得预期的结果。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using System;

namespace WorkingWithClasses
{
class Program
{
    static void Main(string[] args)
    {
        //create 5 player objects
        //Player[] players = new Player[5];


        List<Player> playersList = new List<Player>() {
            new Player
            {
                Skill = 5
            },
            new Player
            {
                Skill = 5
            },
            new Player
            {
                Skill = 5
            },
            new Player
            {
                Skill = 5
            },
            new Player
            {
                Skill = 5
            }
        };

        //assigning a value to a player brings exception error:
     /*   foreach (Player player in playersList)
        {
            player = new Player();


        } */


        float skillSum = 0;
        foreach (Player player in playersList)
        {
            skillSum += (float)player.Skill;
        }

        Console.WriteLine(skillSum);
        Console.WriteLine();
    }

}
class Player
{
    public float? Skill { get; set; }
}

}