C# 如何在foreach循环中处理NullReferenceException?
我总是得到这个错误代码。我知道是什么问题,但我不知道为什么。我猜我的模型是空的,但在我看来,它不是空的。 错误代码: 处理请求时发生未处理的异常。 NullReferenceException:对象引用未设置为对象的实例 这里有点问题:C# 如何在foreach循环中处理NullReferenceException?,c#,asp.net,model-view-controller,foreach,nullreferenceexception,C#,Asp.net,Model View Controller,Foreach,Nullreferenceexception,我总是得到这个错误代码。我知道是什么问题,但我不知道为什么。我猜我的模型是空的,但在我看来,它不是空的。 错误代码: 处理请求时发生未处理的异常。 NullReferenceException:对象引用未设置为对象的实例 这里有点问题:@foreach(模型中的var-emp) 我的看法是: @model IEnumerable<CRUDDemo.Models.EmployeeInfo> @{ ViewData["Title"] = "Index"; Layout =
@foreach(模型中的var-emp)
我的看法是:
@model IEnumerable<CRUDDemo.Models.EmployeeInfo>
@{
ViewData["Title"] = "Index";
Layout = "~/Views/Shared/_Layout.cshtml";
}
<h1>Index</h1>
<p>
<a asp-action="Create">Create New</a>
</p>
@*For Display Employee Info*@
<table class="table table-striped">
<thead>
<tr>
<th>
@Html.DisplayNameFor(model => model.Name)
</th>
<th>
@Html.DisplayNameFor(model => model.Gender)
</th>
<th>
@Html.DisplayNameFor(model => model.Company)
</th>
<th>
@Html.DisplayNameFor(model => model.Department)
</th>
</tr>
</thead>
<tbody>
@foreach(var emp in Model)
{
<tr>
<td>
@Html.DisplayFor(modelItem => emp.Name)
</td>
<td>
@Html.DisplayFor(modelItem => emp.Gender)
</td>
<td>
@Html.DisplayFor(modelItem => emp.Company)
</td>
<td>
@Html.DisplayFor(modelItem => emp.Department)
</td>
<td>
<a asp-action="Edit" asp-route-id="@emp.ID">Edit</a>
<a asp-action="Details" asp-route-id="@emp.ID">Details</a>
<a asp-action="Delete" asp-route-id="@emp.ID">Delete</a>
</td>
</tr>
}
</tbody>
</table>
@model IEnumerable
@{
ViewData[“标题”]=“索引”;
Layout=“~/Views/Shared/_Layout.cshtml”;
}
指数
创造新的
@*用于显示员工信息*@
@DisplayNameFor(model=>model.Name)
@DisplayNameFor(model=>model.Gender)
@DisplayNameFor(model=>model.Company)
@DisplayNameFor(model=>model.Department)
@foreach(模型中的var emp)
{
@DisplayFor(modeleItem=>emp.Name)
@DisplayFor(modeleItem=>emp.Gender)
@DisplayFor(modeleItem=>emp.Company)
@DisplayFor(modelItem=>emp.Department)
编辑
细节
删去
}
我的模型:
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Threading.Tasks;
namespace CRUDDemo.Models
{
public class EmployeeDAL
{
string connectionString = "Data Source=LENOVOL470\\SQLEXPRESS;Initial Catalog=EMPLOYEEDB;Persist Security Info=False;User ID=sa;password=123;";
//Get All
public IEnumerable<EmployeeInfo> GetAllEmployee()
{
List<EmployeeInfo> empList = new List<EmployeeInfo>();
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("SP_GetAllEmployee", con);
cmd.CommandType = System.Data.CommandType.StoredProcedure;
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
EmployeeInfo emp = new EmployeeInfo();
emp.ID = Convert.ToInt32(dr["ID"].ToString());
emp.Name = dr["Name"].ToString();
emp.Gender = dr["Gender"].ToString();
emp.Company = dr["Company"].ToString();
emp.Department = dr["Department"].ToString();
empList.Add(emp);
}
con.Close();
}
return empList;
}
//To Insert Employee
public void AddEmployee(EmployeeInfo emp)
{
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("SP_InsertEmployee", con);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@Name", emp.Name);
cmd.Parameters.AddWithValue("@Gender", emp.Gender);
cmd.Parameters.AddWithValue("@Company", emp.Company);
cmd.Parameters.AddWithValue("@Department", emp.Department);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
//To Update Employee
public void UpdateEmployee(EmployeeInfo emp)
{
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("SP_UpdateEmployee", con);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@EmpId", emp.ID);
cmd.Parameters.AddWithValue("@Name", emp.Name);
cmd.Parameters.AddWithValue("@Gender", emp.Gender);
cmd.Parameters.AddWithValue("@Company", emp.Company);
cmd.Parameters.AddWithValue("@Department", emp.Department);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
//To Delete Employeee
public void DeleteEmployee(int? empId)
{
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("SP_DeleteEmployee", con);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@EmpId", empId);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
//Get Employee by ID
public EmployeeInfo GetEmployeeById(int? empId)
{
EmployeeInfo emp = new EmployeeInfo();
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("SP_GetEmployeeById", con);
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@EmpId", empId);
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
while(dr.Read())
{
emp.ID = Convert.ToInt32(dr["ID"].ToString());
emp.Name = dr["Name"].ToString();
emp.Gender = dr["Gender"].ToString();
emp.Company = dr["Company"].ToString();
emp.Department = dr["Department"].ToString();
}
con.Close();
}
return emp;
}
}
}
使用系统;
使用System.Collections.Generic;
使用系统数据;
使用System.Data.SqlClient;
使用System.Linq;
使用System.Threading.Tasks;
命名空间CRUDDemo.Models
{
公共阶层雇员
{
string connectionString=“数据源=LENOVOL470\\SQLEXPRESS;初始目录=EMPLOYEEDB;持久安全信息=False;用户ID=sa;密码=123;”;
//全部
公共IEnumerable GetAllEmployee()
{
List empList=新列表();
使用(SqlConnection con=newsqlconnection(connectionString))
{
SqlCommand cmd=新的SqlCommand(“SP_GetAllEmployee”,con);
cmd.CommandType=System.Data.CommandType.StoredProcess;
con.Open();
SqlDataReader dr=cmd.ExecuteReader();
while(dr.Read())
{
EmployeeInfo emp=新的EmployeeInfo();
emp.ID=Convert.ToInt32(dr[“ID”].ToString());
emp.Name=dr[“Name”].ToString();
emp.Gender=dr[“Gender”].ToString();
emp.Company=dr[“Company”].ToString();
emp.Department=dr[“Department”].ToString();
雇主添加(emp);
}
con.Close();
}
返回雇主;
}
//插入雇员
公共无效添加员工(员工信息emp)
{
使用(SqlConnection con=newsqlconnection(connectionString))
{
SqlCommand cmd=新的SqlCommand(“SP_InsertEmployee”,con);
cmd.CommandType=CommandType.storedProcess;
cmd.Parameters.AddWithValue(“@Name”,emp.Name);
cmd.Parameters.AddWithValue(“@Gender”,emp.Gender);
cmd.Parameters.AddWithValue(“@Company”,emp.Company);
cmd.Parameters.AddWithValue(“@Department”,emp.Department);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
//更新员工
公共无效更新员工(员工信息emp)
{
使用(SqlConnection con=newsqlconnection(connectionString))
{
SqlCommand cmd=新的SqlCommand(“SP_UpdateEmployee”,con);
cmd.CommandType=CommandType.storedProcess;
cmd.Parameters.AddWithValue(“@EmpId”,emp.ID);
cmd.Parameters.AddWithValue(“@Name”,emp.Name);
cmd.Parameters.AddWithValue(“@Gender”,emp.Gender);
cmd.Parameters.AddWithValue(“@Company”,emp.Company);
cmd.Parameters.AddWithValue(“@Department”,emp.Department);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
//删除雇员
公共无效删除员工(int?empId)
{
使用(SqlConnection con=newsqlconnection(connectionString))
{
SqlCommand cmd=新的SqlCommand(“SP_deletemployee”,con);
cmd.CommandType=CommandType.storedProcess;
cmd.Parameters.AddWithValue(“@EmpId”,EmpId);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
//按ID获取员工
公共EmployeeInfo GetEmployeeById(int?empId)
{
EmployeeInfo emp=新的EmployeeInfo();
使用(SqlConnection con=newsqlconnection(connectionString))
{
SqlCommand cmd=newsqlcommand(“SP_GetEmployeeById”,con);
cmd.CommandType=System.Data.CommandType.StoredProcess;
cmd.Parameters.AddWithValue(“@EmpId”,EmpId);
con.Open();
SqlDataReader dr=cmd.ExecuteReader();
while(dr.Read())
{
emp.ID=Convert.ToInt32(dr[“ID”].ToString());
emp.Name=dr[“Name”].ToString();
emp.Gender=dr[“Gender”].ToString();
emp.Company=dr[“Company”].ToString();
emp.Department=dr[“Department”].ToString();
}
con.Close();
}
返回emp;
}
}
}
我的控制器:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using AspNetCore;
using CRUDDemo.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ActionConstraints;
namespace CRUDDemo.Controllers
{
public class EmployeeController : Controller
{
EmployeeDAL employeeDAL = new EmployeeDAL();
public IActionResult Index()
{
List<EmployeeInfo> empList = new List<EmployeeInfo>();
empList = employeeDAL.GetAllEmployee().ToList();
return View(empList);
}
[HttpGet]
public IActionResult Create()
{
return View();
}
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Create([Bind] EmployeeInfo objEmp)
{
if (ModelState.IsValid)
{
employeeDAL.AddEmployee(objEmp);
return RedirectToAction("Index");
}
return View(objEmp);
}
public IActionResult Edit(int? id)
{
if (id == null)
{
return NotFound();
}
EmployeeInfo emp = employeeDAL.GetEmployeeById(id);
if(emp == null)
{
return NotFound();
}
return View(emp);
}
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Edit(int? id, [Bind] EmployeeInfo objEmp)
{
if (id == null)
{
return NotFound();
}
if (ModelState.IsValid)
{
employeeDAL.UpdateEmployee(objEmp);
return RedirectToAction("Index");
}
return View(employeeDAL);
}
[HttpGet]
public IActionResult Details(int? id)
{
if (id == null)
{
return NotFound();
}
EmployeeInfo emp = employeeDAL.GetEmployeeById(id);
if (emp == null)
{
return NotFound();
}
return View(emp);
}
public IActionResult Delete(int? id)
{
if (id == null)
{
return NotFound();
}
EmployeeInfo emp = employeeDAL.GetEmployeeById(id);
if (emp == null)
{
return NotFound();
}
return View(emp);
}
[HttpPost,ActionName("Delete")]
[ValidateAntiForgeryToken]
public IActionResult DeleteEmp(int? id)
{
employeeDAL.DeleteEmployee(id);
return RedirectToAction("Index");
}
}
}
使用系统;
使用System.Collections.Generic;
使用System.L
@foreach(var emp in Model)
{
@if(emp != null)
{
// bind the properties to UI element
}