从txt文件中读取数据时,我得到空引用异常。
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;
}
}
RecurringAppointment
继承自Appointments
。文件存在,文件位置正确。有趣的是程序在30分钟前工作我只是从下面改变了Load方法,你可以在上面看到:
public bool Load(string fileName)
{
string appointmentData = string.Empty;
using (StreamReader reader = new StreamReader(fileName))
{
while((appointmentData = reader.ReadLine()) != null)
{
appointmentData = reader.ReadLine();
if(appointmentData[0] == 'R')
{
this.Add(appointment = new RecurringAppointment(appointmentData));
}
else
{
this.Add(appointment = new Appointment(appointmentData));
}
}
return true;
}
}
现在它在两种情况下都不起作用。
答案 0 :(得分:3)
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,则在while语句中对null进行检查可使代码进入循环,但后面的ReadLine返回空字符串。当然,尝试读取空字符串的索引零处的char将抛出NRE异常。
您的文件中还存在空行问题。如果存在空行,则再次读取索引零将使索引超出范围异常
您可以通过这种方式修复代码
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;
}
}