来自 TextBox 的 WebControls - 不在 Postaback 上保存新属性

Posted 2023-03-31

【中文标题】来自 TextBox 的 WebControls - 不在 Postaback 上保存新属性

【英文标题】：WebControls From TextBox - Not Saving New Property on Postaback

【发布时间】：2018-04-07 22:29:16

【问题描述】：

我觉得自己是个白痴，应该就这么简单，但似乎行不通。 下面是我的控制代码。

Imports System.Web.UI.WebControls

Public Class PasswordTextBox
            Inherits TextBox
Public Sub New()
    TextMode = TextBoxMode.Password
End Sub

Public Property Password As String
    Get
        Dim s As String = CType(ViewState("Password"), String)
        If s Is Nothing Then Return ""
        Return s
    End Get
    Set(value As String)
        ViewState("Password") = value
    End Set
End Property

Private Const DEFAULT_PASSWORD As String = "********************"
Public Overrides Property Text() As String
    Get
        If Password = "" Then Return ""
        Return DEFAULT_PASSWORD
    End Get
    Set
        MyBase.Text = DEFAULT_PASSWORD
        Attributes("value") = DEFAULT_PASSWORD
    End Set
End Property

Protected Overrides Sub OnPreRender(e As EventArgs)
    MyBase.OnPreRender(e)

    Attributes("value") = Text
End Sub
Protected Overrides Sub Render(ByVal output As System.Web.UI.htmlTextWriter)
    MyBase.Render(output)
End Sub

结束类

目的很简单，覆盖属性以始终显示 ***** 作为值，而是使用新属性 Password 来获取/设置数据。这样当用户在浏览器中使用“Inspect element”功能时，他就无法得到实际的密码。

但是，在页面回发时，当我获得 txtPassword.Password 属性时，它返回一个空字符串。

我有什么遗漏吗？ 谢谢

【参考方案1】：

好的，我能够找到问题所在。我必须从 IPostBackDataHandler 继承，然后重写 LoadPostData 方法。

新类如下所示。

Imports System.Web.UI
Imports System.Web.UI.WebControls


Public Class PasswordTextBox
      Inherits TextBox
      Implements IPostBackDataHandler

Public Sub New()
    TextMode = TextBoxMode.Password
End Sub

Public Property Password As String
    Get
        Dim s As String = CType(ViewState("Password"), String)
        If s Is Nothing Then Return ""
        Return s
    End Get
    Set(value As String)
        ViewState("Password") = value
    End Set
End Property

Private Const DEFAULT_PASSWORD As String = "********************"
Public Overrides Property Text() As String
    Get
        If Password = "" Then Return ""
        Return DEFAULT_PASSWORD
    End Get
    Set
        MyBase.Text = DEFAULT_PASSWORD
        Attributes("value") = DEFAULT_PASSWORD
    End Set
End Property

Protected Overrides Sub OnPreRender(e As EventArgs)
    MyBase.OnPreRender(e)

    Attributes("value") = Text
End Sub
Protected Overrides Sub Render(ByVal output As System.Web.UI.HtmlTextWriter)
    MyBase.Render(output)
End Sub

Public Overridable Shadows Function LoadPostData(postDataKey As String, postCollection As System.Collections.Specialized.NameValueCollection) As Boolean Implements IPostBackDataHandler.LoadPostData
    Dim presentValue As String = Password
    Dim postedValue As String = postCollection(postDataKey)

    If presentValue Is Nothing OrElse Not presentValue.Equals(postedValue) Then
        If postedValue <> DEFAULT_PASSWORD Then Password = postedValue
        Return True
    End If

    Return False
End Function

End Class