C#空引用异常和StreamReader

从txt文件读取数据时出现空引用异常

     public class Appointments : List<Appointment>
        {
            Appointment appointment;

            public Appointments()
            {

            }

            public bool Load(string fileName)
            {
                string appointmentData = string.Empty;
                using (StreamReader reader = new StreamReader(fileName))
                {
                    while((appointmentData = reader.ReadLine()) != null)
                    {
                        appointmentData = reader.ReadLine();
                        //**this is where null ref. exception is thrown** (line below)
                        if(appointmentData[0] == 'R')
                        {
                            appointment = new RecurringAppointment(appointmentData);
                        }
                        else
                        {
                            appointment = new Appointment(appointmentData);
                        }
                        this.Add(appointment);
                    }
                    return true;
                }
            }

---

现在，这两种情况都不起作用。

您的代码在每个循环中读取两次。这意味着，如果在读取文件的最后一行时文件的行数为奇数，则while语句中的null检查允许代码进入循环，但下面的ReadLine返回null字符串。当然，尝试读取空字符串的索引0处的字符将引发NRE异常

文件中还有空行的问题。如果有一个空行，那么再次读取索引0将抛出索引超出范围异常

您可以用这种方式修复代码

public bool Load(string fileName)
{
    string appointmentData = string.Empty;
    using (StreamReader reader = new StreamReader(fileName))
    {
        while((appointmentData = reader.ReadLine()) != null)
        {
            if(!string.IsNullOrWhiteSpace(appointmentData))
            {
                if(appointmentData[0] == 'R')
                    this.Add(appointment = new RecurringAppointment(appointmentData));
                else
                    this.Add(appointment = new Appointment(appointmentData));
            }
        }
        return true;
    }
}

---

除此之外，你还打了两次readline……为什么过了一会儿你还要读另一行？这将在最后一行终止应用程序（如果行数为奇数）。事实上，最后一行将从while中读取，但另一个ReadLine没有要读取的内容并返回null。您是否在文件中添加了新行？我猜是坏习惯：D.删除额外任命后Data=reader.ReadLine（）。我获取的索引超出范围错误。可能是您的文件中的某些内容。（当然，如果您的文件包含空行，那么读取索引[0]处的字符将抛出）请显示输入文件的一些行。这是处理文件读取的好方法：D。感谢您的输入。希望我能给您一些+rep:（。

public bool Load(string fileName)
{
    string appointmentData = string.Empty;
    using (StreamReader reader = new StreamReader(fileName))
    {
        while((appointmentData = reader.ReadLine()) != null)
        {
            if(!string.IsNullOrWhiteSpace(appointmentData))
            {
                if(appointmentData[0] == 'R')
                    this.Add(appointment = new RecurringAppointment(appointmentData));
                else
                    this.Add(appointment = new Appointment(appointmentData));
            }
        }
        return true;
    }
}