对象引用未设置为对象隐藏字段的实例

我的代码有问题

这是我的母版页 HTML 代码

<%@ Master Language="VB" CodeFile="MasterPage.master.vb" Inherits="MasterPage" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title></title>
<asp:ContentPlaceHolder id="head" runat="server">
</asp:ContentPlaceHolder>  
</head>
<body>
<form id="form1" runat="server">
<div class="header" id="header">
    <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
    </asp:ContentPlaceHolder> 
<asp:HiddenField ID="param1" runat="server" />
     <script type="text/javascript">
         function alertMessage() {
             var test = document.getElementById("param1").value;
             alert(test);
         }
     </script>
</div> 
</form>
</body>
</html>

这是我在子页面上调用隐藏字段的代码

Protected Button1_Click(sender as Object, e as EventArgs) Handles Button1.Click
    Dim param1 As HiddenField = DirectCast(Page.Master.FindControl("param1"), HiddenField)
    param1.Value = "Testing"
    Dim csname1 As String = "ClientScript"
    Dim csname2 As String = "alertMessage()"
    Dim cstype As Type = Me.GetType()
    Dim cs As ClientScriptManager = Page.ClientScript
    If (Not cs.IsStartupScriptRegistered(cstype, csname1)) Then
        cs.RegisterClientScriptBlock(cstype, csname1, csname2, True)
    End If
    cs.RegisterStartupScript(cstype, csname1, csname2, True)
End Sub

它使所述对象引用未设置为对象的实例

这是不断抛出错误的代码行

Dim param1 As HiddenField = DirectCast(Page.Master.FindControl("param1"), HiddenField)

谁能帮我???

感谢各种帮助

谢谢

试试这个

Dim param1 As HiddenField =  Me.Page.Master.FindControl("param1")

然后将值分配给该控件。基本上，当您在之前使用隐藏的归档值时给它赋值这个错误来了。

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