Question

我正在使用一个arraylist，并且有这个列表[list.Count -1]，它给了我超出范围异常的参数，为什么呢？如果列表的计数是它包含的元素数，那么列表[list.count]不应该超出范围，这就是我在列表中添加项目的方式：

string query = "SELECT Title, Type, Contents, Rank,Audio FROM dbo.Article,dbo.ArticleJournal WHERE dbo.Article.ArticleId = dbo.ArticleJournal.ArticleId AND dbo.ArticleJournal.JournalId LIKE @id ;";
List<Codes.ArticleJ> list = new List<Codes.ArticleJ>();
using (SqlConnection connection = new SqlConnection(
         connectionString))
{
    SqlCommand command = new SqlCommand(
        query, connection);
    try
    {
        connection.Open();
        command.Parameters.Add(new SqlParameter("@id", id));
        SqlDataReader reader = command.ExecuteReader();

        while (reader.Read())
        {
            string Title = reader.GetString(0);
            string type = reader.GetString(1);
            String Contents = reader.GetString(2);
            int rnk = reader.GetInt32(3);
            String Audio = reader.GetString(4);

            Codes.ArticleJ article = new Codes.ArticleJ(Title, type,     Contents, rnk, Audio);
            list.Add(article);
        }
    }
    finally 
    { 
        connection.Close();
    }
}

然后我这样做：

if (list[list.Count -1].rank == list.Count)

Answer 1

好吧，如果list.count = 0（即一个空列表）并从中减去1，它将抛出该异常。

Answer 2

正如Damon先前所说，如果你有一个从0开始的arraylist并且你从0减去1，那么你得到的-1就数组/ arraylists来说是不存在的。

以这种方式思考，数组超出范围的唯一方法是当程序在不存在时请求数组键。例如：

//Say you had this array
int [] myArray = new int [5];

//Then you wanted to add a number to myArray[6]
myArray[6] = 15;

//You will get the exception because you did not define myArray to have 7 keys (0-6)

//This also goes for negative integers
myArray[-1] = 15; 

//You will also get the exception because 0 is the lowest key an array can go
//Negative numbers do not exist

我有一个超出界限的争论

2 个答案: