asp.net-mvc MVC ASP.NET 没有为此对象定义无参数构造函数

MVC ASP.NET No parameterless constructor defined for this object

提问by Anna Marie Rapa

When I click submit in order to create an account the following error is displayed. I can't find why it is giving the following error. Also I tried to use breakpoints and debugging but it was useless

当我单击提交以创建帐户时，显示以下错误。我找不到为什么会出现以下错误。我也尝试使用断点和调试，但没用

No parameterless constructor defined for this object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.MissingMethodException: No parameterless constructor defined for this object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

没有为此对象定义无参数构造函数。

说明：在执行当前 Web 请求期间发生未处理的异常。请查看堆栈跟踪以获取有关错误及其起源于代码的更多信息。

异常详细信息：System.MissingMethodException：没有为此对象定义无参数构造函数。

源错误：

执行当前 Web 请求期间生成了未处理的异常。可以使用下面的异常堆栈跟踪来识别有关异常来源和位置的信息。

AccountController.cs

账户控制器.cs

    [HandleError]
        public ActionResult CreateNewFixedBankAccount()
        {
            ViewBag.AccountFromList = new SelectList(
           ManageAccount.Instance.GetAccounts(), "accountID", "name");
            ViewBag.AccountTypes = new SelectList(ManageAccountType.Instance.GetNonFixedTypes(), "id", "type");
            ViewBag.Durations = new SelectList(ManageDuration.Instance.GetAllDurations(), "id", "duration1");


            ViewBag.Currencies = new SelectList(ManageCurrency.Instance.getCurrencies(), "id", "symbol");
            return View();


        }

        //
        // POST: /Account/CreateNewFixedBankAccount
        [HttpPost]
        [HandleError]
        public ActionResult CreateNewFixedBankAccount(ViewModel.NewAccountViewModel model, string username)
        {

            return View();
        }

___________________________________________________________________________________________

CreateNewFixedBankAccount.cshtmlThe submit button below gives the error

CreateNewFixedBankAccount.cshtml下面的提交按钮报错

    @model internetBankingApplication.ViewModel.NewFixedAccountViewModel    
    @{
        ViewBag.Title = "CreateNewFixedBankAccount";
    }


    @using (Html.BeginForm())
    {

        ViewBag.Title = "Create";
        Layout = "~/Views/Shared/_Layout.cshtml";
        <fieldset>
            <legend>Fixed Account Details</legend>

            <div class="editor-label">
            <br />
     <b>@Html.LabelFor(model => model.Name)</b>
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.Name)
            </div>

            <div class="editor-label">
            <br />
                <b> @Html.LabelFor(model => model.UserName)</b>
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.UserName)
            </div>

            <div class="editor-label">
            <br />
             <b> @Html.Label("Account From")</b>
            </div>
            <div class="editor-field">
                 @Html.DropDownListFor(model => model.accountFrom, (SelectList)ViewBag.AccountFromList)
            </div>

            <div class="editor-label">
            <br />
               <b>  @Html.LabelFor(model => model.AvailableBalance)</b>
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.AvailableBalance)
            </div>


            <div class="editor-label">
            <br />
     <b>@Html.LabelFor(model => model.currency)</b>
            </div>
            <div class="editor-field">
                 @Html.DropDownListFor(model => model.currency, (SelectList)ViewBag.Currencies)
            </div>

            <div class="editor-label">
            <br />
               <b>  @Html.LabelFor(model => model.Description)</b>
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.Description)
            </div>

            <div class="editor-label">
            <br />
                <b> @Html.LabelFor(model => model.DateOpened)</b>
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.DateOpened)
            </div>


            <div class="editor-label">
            <br />
             <b> @Html.Label("Account Duration")</b>
            </div>
            <div class="editor-field">
                 @Html.DropDownListFor(model => model.duration, (SelectList)ViewBag.Durations)
                 &nbsp;
                  @Html.ActionLink("View Duration Details","DurationDetails","Duration")
            </div>


            <div class="editor-label">
            <br />
             <b> @Html.Label("Account Renew")</b>
            </div>
            <div class="editor-field">
                 @Html.CheckBoxFor(model => model.renew)

            </div>


            <p>
                <input type="submit" value="CreateNewFixedBankAccount" /></p>
        </fieldset>
    }



___________________________________________________________________________________________

NewFixedAccountViewModel.cs

NewFixedAccountViewModel.cs

This view model will get details that have to do with the account from different tables in the database.

此视图模型将从数据库中的不同表中获取与帐户有关的详细信息。

    public class NewFixedAccountViewModel
    {
        private account _Account { get; set; }

        private fixedAccount _FixedAccount { get; set; }

        private int AccountFrom { get; set; }

        public SelectList AccountTypes { get; set; }

        public SelectList Durations { get; set; }

        public SelectList AccountFromList { get; set; }

        public SelectList Currencies { get; set; }

        public int ID
        {
            get
            {
                return _Account.accountID;
            }
        }

        [Required]
        [Display(Name = "Account Name")]
        public string Name
        {
            get
            {
                return _Account.name;
            }
            set
            {
                _Account.name = value;
            }
        }

        [Required]
        [Display(Name = "Account From")]
        public int accountFrom
        {
            get
            {
                return accountFrom;
            }
            set
            {
                accountFrom = value;
            }
        }

        public string AccountFromName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageAccount.Instance.GetAccountBYID(accountFrom).name;
                }
                catch { }
                return result;
            }
        }


        [Required]
        [Display(Name = "Account Type")]
        public int typeID
        {
            get
            {
                return _Account.typeID;
            }
            set
            {
                _Account.typeID = value;
            }
        }

        public string AccountTypeName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageAccountType.Instance.getTypesByID(_Account.typeID).type;
                }
                catch { }
                return result;
            }
        }


        [Required]
        [Display(Name = "Duration")]
        public int duration
        {
            get
            {
                return _FixedAccount.duration;
            }
            set
            {
                _FixedAccount.duration = value;
            }
        }

        public string durationName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageDuration.Instance.GetDurationById(_FixedAccount.duration).duration1;
                }
                catch { }
                return result;
            }
        }

        [Required]
        [Display(Name = "Available Balance")]
        public decimal AvailableBalance
        {
            get
            {
                return _Account.availableBalance;
            }
            set
            {
                _Account.availableBalance = value;
            }
        }

        [Required]
        [Display(Name = "Currency")]
        public int currency
        {
            get
            {
                return _Account.currency;
            }
            set
            {
                _Account.currency = value;
            }
        }

        public string CurrencyName
        {
            get
            {
                string result = string.Empty;
                try
                {
                    result = ManageCurrency.Instance.getTypesByID(_Account.currency).name;
                }
                catch { }
                return result;
            }
        }


        [Required]
        [Display(Name = "Account Description")]
        public string Description
        {
            get
            {
                return _Account.description;
            }
            set
            {
                _Account.description = value;
            }
        }


        [Required]
        [Display(Name = "Account Renew")]
        public bool renew
        {
            get
            {
                if (_FixedAccount.renew == 0)
                {
                    return false;
                }
                return true;
            }
            set
            {
                if (value == false)
                {
                    _FixedAccount.renew = 0;
                }
                else
                {

                    _FixedAccount.renew = 1;
                }
            }
        }


        [Required]
        [Display(Name = "Date Opened")]
        public DateTime DateOpened
        {
            get
            {
                return _Account.dateOpened;
            }
            set
            {
                _Account.dateOpened = value;
            }
        }

        [Required]
        [Display(Name = "Username")]
        public string UserName
        {
            get
            {
                return _Account.username;
            }
            set
            {
                _Account.username = value;
            }
        }

        public NewFixedAccountViewModel(string username)
        {
            AccountTypes = new SelectList(
            ManageAccountType.Instance.getTypes(), "id", "type", _Account.typeID);


            AccountFromList = new SelectList(
            ManageAccount.Instance.GetUserAccounts(username), "accountID", "name", accountFrom);

            Currencies = new SelectList(
            ManageCurrency.Instance.getCurrencies(), "id", "name", _Account.currency);

            Durations = new SelectList(
            ManageDuration.Instance.GetAllDurations(), "id", "duration", _FixedAccount.duration);


        }

        public NewFixedAccountViewModel(int accountID, string username)
        {
            _Account = ManageAccount.Instance.GetAccountBYID(accountID);

            _FixedAccount = ManageFixedAccount.Instance.GetFixedAccountByID(accountID);

            AccountFromList = new SelectList(
            ManageAccount.Instance.GetUserAccounts(username), "accountID", "name", accountFrom);

            AccountTypes = new SelectList(
            ManageAccountType.Instance.getTypes(), "id", "type", _Account.accountType);

            Currencies = new SelectList(
            ManageCurrency.Instance.getCurrencies(), "id", "name", _Account.currency);

            Durations = new SelectList(
            ManageDuration.Instance.GetAllDurations(), "id", "duration", _FixedAccount.duration);


        }

回答by Adelia Benalius

it's because you don't have parameterless constructor in your ViewModel class. You have 2 constructors there:

这是因为您的 ViewModel 类中没有无参数构造函数。您在那里有 2 个构造函数：

• public NewFixedAccountViewModel(string username)
• public NewFixedAccountViewModel(int accountID, string username)

• public NewFixedAccountViewModel（字符串用户名）
• public NewFixedAccountViewModel(int accountID, string username)

When you submit the form, during model binding, the controller is trying to create a new instance of the model, but it doesn't find parameterless constructor.

当您提交表单时，在模型绑定期间，控制器会尝试创建模型的新实例，但找不到无参数构造函数。

So you need to have:

所以你需要有：

public NewFixedAccountViewModel() { 
// Your code here 
}

What you can do is maybe use the Username property instead of username parameter, so your code will be:

您可以做的是使用 Username 属性而不是 username 参数，因此您的代码将是：

public NewFixedAccountViewModel()
    {
        AccountTypes = new SelectList(
        ManageAccountType.Instance.getTypes(), "id", "type", _Account.typeID);


        AccountFromList = new SelectList(
        ManageAccount.Instance.GetUserAccounts(Username), "accountID", "name", accountFrom);

        Currencies = new SelectList(
        ManageCurrency.Instance.getCurrencies(), "id", "name", _Account.currency);

        Durations = new SelectList(
        ManageDuration.Instance.GetAllDurations(), "id", "duration", _FixedAccount.duration);

    }

回答by ssn771

I'm not sure if this is quite right, but I think what's happening is you've declared constructors for your model. So it is trying to create a new object based on your model class, but can't because there isn't a constructor that accepts no parameters. I think what you need to do is create a new model in your controller with one of the constructors you have defined and pass it to the view:

我不确定这是否完全正确，但我认为发生的事情是您已经为您的模型声明了构造函数。所以它试图根据您的模型类创建一个新对象，但不能，因为没有一个不接受任何参数的构造函数。我认为您需要做的是在您的控制器中使用您定义的构造函数之一创建一个新模型并将其传递给视图：

NewFixedAccountViewModel model = new NewFixedAccountViewModel(username);
return View(model);

Then it'll bind to the model object you have created with the appropriate constructor and bind the form fields to that instead instead of trying to create a new one.

然后它将绑定到您使用适当的构造函数创建的模型对象，并将表单字段绑定到该对象，而不是尝试创建一个新的。