嘗試在ASP.NET 4.5中覆蓋HtmlGenericControl時出錯

Question

我有以下課程：

Public Class HtmlGenericSelfClosingTag
    Inherits HtmlGenericControl
    Public Sub New()
        MyBase.New()
    End Sub
    Public Sub New(tag As String)
        MyBase.New(tag)
    End Sub
    Public Shadows Property TagName As String
        Get
            Return MyBase.TagName
        End Get
        Set(value As String)
            MyBase.TagName = value
        End Set
    End Property
    Public Overrides ReadOnly Property Controls As ControlCollection
        Get
            Throw New Exception("HtmlGenericSelfClosingTag cannot have child controls.")
        End Get
    End Property
    Public Overrides Property InnerHtml As String
        Get
            Return String.Empty
        End Get
        Set(value As String)
            Throw New Exception("InnerHtml cannot be set on an HtmlGenericSelfClosingTag")
        End Set
    End Property
    Public Overrides Property InnerText As String
        Get
            Return String.Empty
        End Get
        Set(value As String)
            Throw New Exception("InnerText cannot be set on an HtmlGenericSelfClosingTag")
        End Set
    End Property
    Public Overrides Sub RenderControl(writer As HtmlTextWriter)
        MyBase.Render(writer)
        writer.Write(HtmlTextWriter.TagLeftChar & Me.TagName)
        Attributes.Render(writer)
        writer.Write(HtmlTextWriter.SelfClosingTagEnd)
    End Sub
End Class

我已經聲明控件為：

Protected WithEvents MyElement As HtmlGenericSelfClosingTag

我將html標記定義為：

<HtmlGenericSelfClosingTag ID="MyElement" runat="server" />

在頁面渲染期間出現以下錯誤：

基類包含字段“ MyElement”，但其類型（MyClass.HtmlGenericSelfClosingTag）與控件的類型（System.Web.UI.HtmlControls.HtmlGenericControl）不兼容。

我已經搜索了DuckDuckGo（以及擴展名，Google等），以找出我需要重寫的其他內容，以使我的類與HtmlGenericControl類兼容，但沒有骰子。 我還檢查了MSDN文檔，但沒有提及覆蓋要求。 有任何想法嗎？

Answer 1

通過從aspx文件中刪除<HtmlGenericSelfClosingTag ID="MyElement" runat="server" />標記，然后直接在代碼中直接添加控件，就可以解決該問題，如下所示：

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Me.head.Controls.AddAt(0, BaseElement)
End Sub

為了避免兩次呈現控件，我修改了Render代碼：

Public Overrides Sub RenderControl(writer As HtmlTextWriter)
    writer.Write(HtmlTextWriter.TagLeftChar & Me.TagName)
    Attributes.Render(writer)
    writer.Write(HtmlTextWriter.SelfClosingTagEnd)
End Sub