错误是“对象引用未设置为对象的实例” [英] Error is "Object reference not set to an instance of an object"

问题描述

我有一个问题，当我运行我的代码，然后发生错误对象引用未设置为对象的实例。

  void btn_Save_Click（object sender，EventArgs e）
 {
 string str =（Provider = Microsoft.ACE.OLEDB.12.0; Data Source = C：/Users/Geeta/Desktop/eTimeTrackLite1.mdb; Persist Security Info = False;）; 
 OleDbConnection conn = new OleDbConnection（str）; 
 conn.Open（）; 
 string query =insert into Employees（[EmployeeName]，EmployeeCode，DeviceCode，Company，Department，Designation，Grade，Team，Location，EmploymentType，Category，HolidayGroup，ShiftGroup，ShiftRoster，Dateofjoining，Dateofconfirmation，Status，DateofResigning， [Sex]）values（'+ txt_empname.Text +'，'+ txt_code.Text +'，'+ txt_dcode.Text +'，'+ dp_company.SelectedItem.ToString '+ dp_department.SelectedItem.ToString（）+'，'+ dp_designation.SelectedItem.ToString（）+'，'+ dp_grade.SelectedItem.ToString（）+'，'+ dp_team.SelectedItem.ToString （）+'，'+ dp_location.SelectedItem.ToString（）+'，'+ dp_emptype.SelectedItem.ToString（）+'，'+ dp_category.SelectedItem.ToString + dp_holigroup.SelectedItem.ToString（）+'，'+ dp_shiftgroup.SelectedItem.ToString（）+'，'+ dp_shiftroster.SelectedItem.ToString（）+'，'+ dp_day.SelectedItem.ToString +'，'+ dp_month.SelectedItem.ToString（）+'，'+ dp_year.SelectedItem.ToString（）+'，'+ dp_cday.SelectedItem.ToString（）+'，'+ dp_cmonth .SelectedItem.ToString（）+'，'+ dp_cyear.SelectedItem.ToString（）+'，'+ dp_status.SelectedItem.ToString（）+'，'+ dp_rday.SelectedItem.ToString '，'+ dp_rmonth.SelectedItem.ToString（）+'，'+ dp_ryear.SelectedItem.ToString（）+'，'+ rdbtn_male.Checked.ToString（）+'，'+ rdbtn_female.Checked ToString（）+'）; 
 OleDbCommand cmd = new OleDbCommand（query，conn）; 
 cmd.ExecuteNonQuery（）; 
 conn.Close（）; 
 BindGridData（）; 
} 
  

感谢

解决方案

为了避免这种问题，不要使用ToString是有调用对象为null的风险，使用Convert.ToString（）。
http://msdn.microsoft.com/en -us / library / system.convert.tostring.aspx

i have a problem, when i m run my code then error is occured that "Object reference not set to an instance of an object."

plz suggest me regarding that.

Code

protected void btn_Save_Click(object sender, EventArgs e)
    {
        string str = ("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:/Users/Geeta/Desktop/eTimeTrackLite1.mdb;Persist Security Info=False;");
        OleDbConnection conn = new OleDbConnection(str);
        conn.Open();
        string query = "insert into Employees ([EmployeeName],EmployeeCode,DeviceCode,Company,Department,Designation,Grade,Team,Location,EmploymentType,Category,HolidayGroup,ShiftGroup,ShiftRoster,Dateofjoining,Dateofconfirmation,Status,DateofResigning,[Sex]) values ('" + txt_empname.Text + "','" + txt_code.Text + "', '" + txt_dcode.Text + "', '" + dp_company.SelectedItem.ToString() + "', '" + dp_department.SelectedItem.ToString() + "', '"+dp_designation.SelectedItem.ToString()+"', '"+dp_grade.SelectedItem.ToString()+"', '"+dp_team.SelectedItem.ToString()+"', '"+dp_location.SelectedItem.ToString()+"', '"+dp_emptype.SelectedItem.ToString()+"', '"+dp_category.SelectedItem.ToString()+"', '"+dp_holigroup.SelectedItem.ToString()+"', '"+dp_shiftgroup.SelectedItem.ToString()+"', '"+dp_shiftroster.SelectedItem.ToString()+"', '"+dp_day.SelectedItem.ToString()+"', '"+dp_month.SelectedItem.ToString()+"', '"+dp_year.SelectedItem.ToString()+"', '"+dp_cday.SelectedItem.ToString()+"', '"+dp_cmonth.SelectedItem.ToString()+"', '"+dp_cyear.SelectedItem.ToString()+"', '"+dp_status.SelectedItem.ToString()+"', '"+dp_rday.SelectedItem.ToString()+"', '"+dp_rmonth.SelectedItem.ToString()+"', '"+dp_ryear.SelectedItem.ToString()+"', '"+rdbtn_male.Checked.ToString()+"', '"+rdbtn_female.Checked.ToString()+"')";
        OleDbCommand cmd = new OleDbCommand(query, conn);
        cmd.ExecuteNonQuery();
        conn.Close();
        BindGridData();
    }

"Thanks"

解决方案

In order to avoid this kind of problems, don't use ToString is there is a risk of the calling object to be null, use Convert.ToString() instead. http://msdn.microsoft.com/en-us/library/system.convert.tostring.aspx

这篇关于错误是“对象引用未设置为对象的实例”的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！