Question

为什么这个Application对象没有实例化？每当我运行代码时它都为null。

public class Applicant
{
    private Application oApplication = new Application();

    public Applicant()
    { 
        oApplication = new Application();
    }

    public Application Application
    {
        get { return oApplication; }
        set { oApplication = value; }
    }             
}

这是应用程序类

    public class Application
{
    public string ApplicationID { get; set; }
    public ContactDetails ContactDetails { get; set; }   
}

这是调用代码......

        public Applicant[] GetApplicants()
    {
        Applicant[] oApplicant;

        DataSet dsExcelSchema = new DataSet();
        dsExcelSchema = GetDataAsDataSet();

        DataTable contactInfoTable = dsExcelSchema.Tables["ContactInformation$"];
        int numOfApplications = contactInfoTable.Rows.Count - 1;
        int i = 0;

        oApplicant = new Applicant[numOfApplications];

        foreach (DataRow dr in contactInfoTable.Rows)
        {
            Application oApplication = new Application();

            oApplicant[i].Application.ApplicationID = dr["ApplicationID"].ToString();
            i++;
        }
        return oApplicant;
    }

它给我一个NullReferenceException。

Answer 1

您忘记在数组元素中创建申请人的实例 - 应该这样做：

foreach (DataRow dr in contactInfoTable.Rows)
{
    oApplicant[i] = new Applicant();
    oApplicant[i].Application.ApplicationID = dr["ApplicationID"].ToString();
    i++;
}

Answer 2

创建对象数组时：

oApplicant = new Applicant[numOfApplications];

将填充nulls。因此，您需要首先使用实际值初始化它：

for (int i = 0; i < numOfApplications; i++)
{
    oApplicant[i] = new Applicant();
}

Answer 3

除了其他答案之外，您还需要将numOfApplications设置为contactInfoTable.Rows.Count，而不是contactInfoTable.Rows.Count - 1;

int numOfApplications = contactInfoTable.Rows.Count;

为什么我的C＃对象没有实例化？

3 个答案: