Question

我有一个绑定到用户类列表的数据网格视图。

当我创建一个新行时，我得到一个缺少的方法异常＆＃34;找不到User.cs上的构造函数＆＃34;。问题是我已经有一个默认的构造函数所以我想知道是否有办法找出参数是什么，以便我可以实现类构造函数。

这是类和构造函数

    public string Username { get; set; }
    public byte[] HashedPassword;
    public byte[] Salt ;
    public string sSalt { get { return Encoding.ASCII.GetString(Salt); } set; }
    public string sPass { get { return Encoding.ASCII.GetString(HashedPassword); } set; }
    public bool Admin { get; set; }
    public List<AnswerClass> answers { get; set; }
    public Tuple<int, int> sessionScore;

    public User(string UsernameArg = "", byte[] PasswordArg = null, byte[] SaltArg = null, bool AdminArg = false)
    {
        sessionScore = new Tuple<int, int>(0, 0);
        Username = UsernameArg;
        HashedPassword = PasswordArg;
        Salt = SaltArg;
        Admin = AdminArg;
        answers = new List<AnswerClass>();
    }

错误：

System.MissingMethodException was unhandled
HResult=-2146233069
Message=Constructor on type 'QuizProject_SourceControl_.User' not found.
Source=mscorlib
StackTrace:
   at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture)
   at System.SecurityUtils.SecureCreateInstance(Type type, Object[] args, Boolean allowNonPublic)
   at System.ComponentModel.BindingList`1.AddNewCore()
   at System.ComponentModel.BindingList`1.System.ComponentModel.IBindingList.AddNew()
   at System.Windows.Forms.CurrencyManager.AddNew()
   at System.Windows.Forms.DataGridView.DataGridViewDataConnection.AddNew()
   at System.Windows.Forms.DataGridView.DataGridViewDataConnection.OnNewRowNeeded()
   at System.Windows.Forms.DataGridView.OnRowEnter(DataGridViewCell& dataGridViewCell, Int32 columnIndex, Int32 rowIndex, Boolean canCreateNewRow, Boolean validationFailureOccurred)
   at System.Windows.Forms.DataGridView.SetCurrentCellAddressCore(Int32 columnIndex, Int32 rowIndex, Boolean setAnchorCellAddress, Boolean validateCurrentCell, Boolean throughMouseClick)
   at System.Windows.Forms.DataGridView.OnCellMouseDown(HitTestInfo hti, Boolean isShiftDown, Boolean isControlDown)
   at System.Windows.Forms.DataGridView.OnCellMouseDown(DataGridViewCellMouseEventArgs e)
   at System.Windows.Forms.DataGridView.OnMouseDown(MouseEventArgs e)
   at System.Windows.Forms.Control.WmMouseDown(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.DataGridView.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
   at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at QuizProject_SourceControl_.Program.Main() in d:\Programming\Repos\QuizProject(SourceControl)\QuizProject(SourceControl)\Program.cs:line 19
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()
InnerException:

Answer 1

您没有默认构造函数。默认构造函数是没有任何参数的构造函数：

public User()
{
    ...
}

您所拥有的是一个构造函数，其中所有参数都具有默认值。这是一个很大的区别，因此原因是参数的默认值在.NET中的工作方式：
在.NET中，编译器将默认值复制到您调用该构造函数（或任何其他方法）的每个位置。所以基本上，参数的默认值只是语法糖。

例：
假设您有这样的方法：

public void Method(int para = 12)
{
}

现在，在代码的某处，您可以这样称呼它：

Method();

编译器将更改此内容，实际编译的代码将如下所示：

public void Method(int para)
{
}

Method(12);

缺少方法异常 - 找出所需的方法

1 个答案: