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我是新來的asp.net mvc和我有一些問題。我想要做的是在索引上顯示div，以便用戶輸入名稱並從下拉列表中選擇值。然後在「生成密碼」上隱藏起始div並顯示div「Hi'UserName''你輸入了'value1'，'value2'。最終我想要的是捕獲UserName並使用下拉列表中的值創建一個隨機密碼（還沒有啓動該模塊，但「呃」，它會做的是說你好'用戶名'你的新密碼是'密碼'，密碼將包含他們選擇的長度和最大數量的字母字符他們想要的。每次我嘗試我碰到下面的錯誤。隱藏在索引導致錯誤顯示科
System.NullReferenceException was unhandled by user code
這個
@Html.DropDownListFor(m => m.LenOfPass, Model.Lengths, "Please select...", new { @class = "form-control" })
[更新的代碼基於@哈尼的迴應]
新代碼相同的錯誤;
控制器;
using System;
using PassGen.Models;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.ComponentModel.DataAnnotations;
namespace PassGen.Controllers
{
public class HomeController : Controller
{
private IEnumerable<int> GetLengths()
{
return new List<int>
{
8,10,15,20,25
};
}
private IEnumerable<int> GetAlpha()
{
return new List<int>
{
1,2,3,4,5
};
}
private IEnumerable<SelectListItem> GetLengthList(IEnumerable<int> elements)
{
var passLens = new List<SelectListItem>();
foreach (var len in elements)
{
string lengths = Convert.ToString(len);
passLens.Add(new SelectListItem { Value = lengths, Text = lengths });
}
return passLens;
}
private IEnumerable<SelectListItem> GetAlphaList(IEnumerable<int> element)
{
var alphaMax = new List<SelectListItem>();
foreach (var alpha in element)
{
string alphas = Convert.ToString(alpha);
alphaMax.Add(new SelectListItem { Value = alphas, Text = alphas });
}
return alphaMax;
}
[HttpGet]
public ViewResult Index()
{
ViewBag.ShowDetails = false;
var LenOfPass = GetLengths();
var MaxOfAlpha = GetAlpha();
var model = new PassGenerator();
model.LenOfPass = new List<SelectListItem>(); // Note initialization of the property
model.Lengths = GetLengthList(LenOfPass);
model.Alphas = GetAlphaList(MaxOfAlpha);
return View(model);
}
[HttpPost]
public ActionResult Index(PassGenerator response)
{
ViewBag.ShowDetails = false;
if (ModelState.IsValid)
{
ViewBag.ShowDetails = true;
ViewBag.UserName = response.UserName;
ViewBag.PassLength = response.LenOfPass;
ViewBag.AlphaMax = response.MaxOfAlpha;
return PartialView ("Index",response);
}
else
{
//There is a validation error
return View();
}
}
}
}
Model;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Security;
using System.Security.Cryptography;
using System.ComponentModel.DataAnnotations;
using System.Text;
namespace PassGen.Models
{
public class PassGenerator
{
[Required(ErrorMessage = "Please enter your name!")]
public string UserName { get; set; }
//This property will hold Length of password chosen by User.
[Required(ErrorMessage = "Please choose a length for your password!")]
public int LenOfPass { get; set; }
//This will hold Lengths for selection
public IEnumerable<SelectListItem> Lengths { get; set;}
//This property will hold Maximum number of Alphanumeric characters chosen by User.
[Required(ErrorMessage = "Please choose the maximum number of alphanumeric characters that you want included!")]
public int MaxOfAlpha { get; set; }
//This will hold values for Max Alphanumeric.
public IEnumerable<SelectListItem> Alphas { get; set;}
//This property will hold the Random Password that is generated
public string RandPass { get; set;}
}
}
索引沒有改變，請原諒我作爲一個新手對此。 指數：
@model PassGen.Models.PassGenerator
@{
Layout = null;
}
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width" />
<title>Index</title>
<script src="~/Scripts/jquery-2.1.1.min.js" type="text/javascript"></script>
</head>
<body>
<div class="inital-form">
@using (Html.BeginForm()) {
@Html.ValidationSummary()
<p>Your Name: @Html.TextBoxFor(x => x.UserName)</p>
<p>Please choose the length of your password:
@Html.DropDownListFor(m => m.LenOfPass, Model.Lengths, "Please select...", new { @class = "form-control" })
</p>
<p>Please choose the Maximum number of Alphanumeric characters you would like included:
@Html.DropDownListFor(m => m.MaxOfAlpha, Model.Alphas, "Please select...", new { @class = "form-control" })
</p>
<input type="submit" value="Generate Your Password" />
}
</div>
@if (ViewBag.ShowDetails) {
<div class="response-section">
<h1>Hello @Html.DisplayFor(m => m.UserName)</h1>
<p>You have entered the following information;</p>
<ul>
<li>Your requested length for your password: @Html.DisplayFor(m => m.LenOfPass)</li>
<li>Maximum number of Alphanumeric Characters required: @Html.DisplayFor(m => m.MaxOfAlpha)</li>
</ul>
</div>
}
</body>
</html>
您還有這個：model.LenOfPass = new List（）。你的模型的這個屬性是一個int，而不是List 。 –
@MattyM我還是不明白。你是說我應該將模型代碼更改爲public List LenOfPass {get;組; }？我試過了，現在我明白了。 App_Web_ncrwhue0.dll中發生類型'System.NullReferenceException'的異常，但未在用戶代碼中處理 附加信息：未將對象引用設置爲對象的實例。 –
daspixl
幾乎所有的'NullReferenceException'都是一樣的。請參閱「[什麼是.NET中的NullReferenceException？]（http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net）」的一些提示。 –