我当前在代码块上遇到此错误。请评论或提供建议如何解决此问题。谢谢。
"An unhandled exception of type 'System.NullReferenceException' occurred in HHONamespace.exe"
Additional information: Object reference not set to an instance of an object."
问题很简单,在将editRecord变量铸造为手动时间之前,我将在其中的列表框中获得选定的记录值时,我会得到一个空。我测试了调试器,即使它是从同一手动时间类构成的列表记录,也读取了NULL,即这很难解释,可能会发生什么?为什么断开将属性写入此变量随后的编辑器表单的连接?由于此变量实例,编辑器形式中的构造函数失败是null引用。该代码工作直到最终施放数据结构,这很奇怪。
private void editBtn_Click(object sender, EventArgs e)
{
//NEEDS SOME DEBUGGING
//Choose a record and select in listbox
if (listHoursLog.SelectedIndex >= 0)
{
var selection = listHoursLog.SelectedItem.ToString();
//Identify manually entered records from timer records that begin with "M"
if (listHoursLog.SelectedIndex >= 0 && selection.StartsWith("M"))
{
ManualTime editRecord = listHoursLog.SelectedItem as ManualTime;
//Launch editor
ManualHours newForm = new ManualHours(editRecord);
newForm.ShowDialog();
if (newForm.ShowDialog() == DialogResult.OK)
{
if (editRecord != null)
{
listHoursLog.Items.Add(editRecord);
}
}
}
else
MessageBox.Show("You may edit only the manually entered records.");
}
}
}
}
...手动Hourhours编辑器表单使用此构造函数...
namespace LOG
{
public partial class ManualHours : Form
{
public ManualHours()
{
InitializeComponent();
}
public ManualHours(ManualTime recordE)
{
InitializeComponent();
//construct the prior data
startDateTimePicker.Value = recordE.date;
/*Need to parse the hours and mins to decimal*/
hrsUpDown.Value = Convert.ToDecimal(recordE.hours.TotalHours);
minsUpDown.Value = Convert.ToDecimal(recordE.mins.TotalMinutes);
}
这是手动时间类...很简单。
namespace LOG
{
public class ManualTime
{
public DateTime date { get; set; }
public TimeSpan hours { get; set; }
public TimeSpan mins { get; set; }
public TimeSpan totalTime { get; set; }
public ManualTime()
{
date = DateTime.Now;
}
public override string ToString()
{
//For list of log records
return string.Format("Manual entry; Date: {0}, ({1} hours + {2} mins) = Total Time: {3}",
this.date.ToShortDateString(),
this.hours, this.mins,
totalTime.ToString(@"hh:mm:ss"));
}
}
}
我认为这行是错误的:
ManualTime editRecord = listHoursLog.SelectedItem as ManualTime;
您需要转换选定的项目为手动时间,而不是 cast it。演员将始终返回null,因此错误。
如果所选项目是字符串,则可以在手动时间类中编写一个parse()函数来转换字符串,类似于toString()functions的反面。