c# - 你调用的对象是空的

Question

我已经分配了两个字符串数组:

string[] SelectColumns = {},WhereColumns={};

两者都充满了数据项。例如 SelectColumns.length = 7,WhereColumns.Length=3;

当我去实现它们时，我遇到了一个异常:未将对象引用设置为对象的实例。我在下面使用它们:

for (int i = 0; i < SelectColumns.Length; i++)
{
    DPS._SelectCol[i] = SelectColumns[i];
}

for (int i = 0; i < WhereColumns.Length; i++)
{
    DPS._WhereCol[i] = WhereColumns[i];
}

这里的DPS是一个类的对象，如下所示:

public class DefaultProfileSetting
{
    private string Server;

    public string _Server
    {
        get { return Server; }
        set { Server = value; }
    }

    private string Authentication;

    public string _Authentication
    {
        get { return Authentication; }
        set { Authentication = value; }
    }
    private string Login;

    public string _Login
    {
        get { return Login; }
        set { Login = value; }
    }
    private string Pass;

    public string _Pass
    {
        get { return Pass; }
        set { Pass = value; }
    }
    private string DB;

    public string _DB
    {
        get { return DB; }
        set { DB = value; }
    }
    private string Table;

    public string _Table
    {
        get { return Table; }
        set { Table = value; }
    }
    private string[] SelectCol;

    public string[] _SelectCol
    {
        get { return SelectCol; }
        set { SelectCol = value; }
    }
    private string[] WhereCol;

    public string[] _WhereCol
    {
        get { return WhereCol; }
        set { WhereCol = value; }
    }
}

Answer 1

您可能只有字符串数组引用 _SelectCol 而不是实际数组，需要实例化 _SelectCol 字符串数组以为其元素分配内存。

DPS._SelectCol = new string [SelectColumns.Length];

for (int i = 0; i < SelectColumns.Length; i++)
{
    DPS._SelectCol[i] = SelectColumns[i];
}