返回MissingMethodException的组合框的强类型列表

Question

好的，所以关于这类错误的帖子很多，但没有什么特别的东西让我能够缩小这个问题。

SqlConnection con = null;
        List<State> list = new List<State>();
        try
        {
            con = Common.openConnection(Common.connectionString);
            string sql = "Select * from State order by state";
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                State m = new State(int.Parse(reader.GetValue(0).ToString()),reader.GetString(1), reader.GetString(2), int.Parse(reader.GetValue(3).ToString()));
                list.Add(m);
            }
            reader.Close();
        }
        catch (Exception ex)
        {
            throw new Exception("Error:[DALStateSQL] in selectAll : " + Common.NEWLINE + ex.ToString());
        }
        finally
        {
            Common.closeConnection(con);
        }
        return list;

这是导致问题的方法。我只是试图将它绑定到对象数据源并将其显示在列表框中。我得到了这个堆栈跟踪：

[MissingMethodException: No parameterless constructor defined for this object.]
System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0
System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache) +98
System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean skipCheckThis, Boolean fillCache) +241
System.Activator.CreateInstance(Type type, Boolean nonPublic) +69
System.Web.UI.WebControls.ObjectDataSourceView.InvokeMethod(ObjectDataSourceMethod method, Boolean disposeInstance, Object& instance) +138
System.Web.UI.WebControls.ObjectDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments) +1953
System.Web.UI.WebControls.ListControl.OnDataBinding(EventArgs e) +97
System.Web.UI.WebControls.ListControl.PerformSelect() +34
System.Web.UI.WebControls.BaseDataBoundControl.DataBind() +74
System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() +66
System.Web.UI.WebControls.ListControl.OnPreRender(EventArgs e) +29
System.Web.UI.Control.PreRenderRecursiveInternal() +103
System.Web.UI.Control.PreRenderRecursiveInternal() +175
System.Web.UI.Control.PreRenderRecursiveInternal() +175
System.Web.UI.Control.PreRenderRecursiveInternal() +175
System.Web.UI.Control.PreRenderRecursiveInternal() +175
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2496

这告诉我一切，因为跟踪中没有任何东西是我自己的代码。

我有另一个相同的方法，它有效，它只是一个行为不端的方法的复制粘贴。州级本身很简单：

private int stateId;
    private string stateCode;
    private string name;
    private int countryCode;

    public int StateId
    {
        get { return stateId; }
        set { stateId = value; }
    }

    public string StateCode
    {
        get { return stateCode; }
        set { stateCode = value; }
    }

    public string Name
    {
        get { return name; }
        set { name = value; }
    }

    public int CountryCode
    {
        get { return countryCode; }
        set { countryCode = value; }
    }

    public State()
    {
        this.stateId = 0;
        this.stateCode = "";
        this.name = "";
        this.countryCode = 0;
    }

    public State(int stateId, string stateCode, string name, int countryCode)
    {
        this.stateId = stateId;
        this.stateCode = stateCode;
        this.name = name;
        this.countryCode = countryCode;
    }

编辑：我忘了在其他地方完全提到selectAll（）方法调用，但在尝试将其绑定到对象数据源时会中断。 .....？