有人可以帮助我理解为什么我的文本框的占位符在选择单选按钮时没有改变吗？

Question

我的 RadioButtonList 的 HTML 源代码：

<asp:RadioButtonList id="rbMemberType" runat="server">
    <asp:ListItem Value="Customer" Selected >Customer</asp:ListItem> 
    <asp:ListItem Value="Employee">Employee</asp:ListItem> 
    <asp:ListItem Value="Supplier">Supplier</asp:ListItem>
    <asp:ListItem Value="Administrator">Administrator</asp:ListItem> 
</asp:RadioButtonList>

我的单选按钮列表选定索引已更改事件的 C# 代码：

 protected void rbMemberType_SelectedIndexChanged(object sender, EventArgs e)
 {
    if (rbMemberType.SelectedValue == "Customer")
    {
        txtUsername.Attributes.Add("placeholder", "Your Customer's Username  *");
        txtPassword.Attributes.Add("placeholder", "Your Customer's Password  *");
    }
    else if (rbMemberType.SelectedValue == "Employee")
    {
        txtUsername.Attributes.Add("placeholder", "Your Employee's Username  *");
        txtPassword.Attributes.Add("placeholder", "Your Employee's Password  *");
    }
    else if (rbMemberType.SelectedValue == "Supplier")
    {
        txtUsername.Attributes.Add("placeholder", "Your Supplier's Username  *");
        txtPassword.Attributes.Add("placeholder", "Your Supplier's Password  *");
    }
    else
    {
        txtUsername.Attributes.Add("placeholder", "Your Administrator's Username  *");
        txtPassword.Attributes.Add("placeholder", "Your Administrator's Password  *");
    }
}

我想做的是，例如。如果选择了"员工单选按钮"，则 Txt用户名的占位符将为"您员工的用户名"，TxtPassword 的占位符将为"您员工的密码"。

我的两个文本框：

<div class="form-group">
    <asp:TextBox class="form-control" runat="server" id="txtUsername"/>
</div>
<div class="form-group">
    <asp:TextBox class="form-control"  runat="server" id="txtPassword" 
    autocomplete="new-password"/> 
</div>

Answer 1

要"立即"获得该更改，您需要启用自动回发，并声明OnSelectedIndexChanged偶数。设置该组后，单击单选按钮时将获得回发，并且将触发 SelectedIndexChanged。

<asp:RadioButtonList 
    id="rbMemberType" 
    runat="server" 
    OnSelectedIndexChanged="rbMemberType_SelectedIndexChanged" 
    AutoPostback="true">

Answer 2

将单选按钮替换为以下代码片段

 <asp:RadioButtonList ID="rbMemberType" runat="server" OnSelectedIndexChanged="rbMemberType_SelectedIndexChanged" AutoPostBack="true">
                <asp:ListItem Value="Customer" Selected>Customer</asp:ListItem>
                <asp:ListItem Value="Employee">Employee</asp:ListItem>
                <asp:ListItem Value="Supplier">Supplier</asp:ListItem>
                <asp:ListItem Value="Administrator">Administrator</asp:ListItem>
            </asp:RadioButtonList>

你失踪了

OnSelectedIndexChanged="rbMemberType_SelectedIndexChanged" AutoPostBack="true"