LINQ查询到WebControl.Controls

Question

我在页面上有三个TextBox控件

<asp:TextBox ID="TextBox1" runat="server" AutoPostBack="True"
        OnTextChanged="TextBox_TextChanged" TabIndex="1">
<asp:TextBox ID="TextBox2" runat="server" AutoPostBack="True"
        OnTextChanged="TextBox_TextChanged" TabIndex="2">
<asp:TextBox ID="TextBox3" runat="server" AutoPostBack="True"
        OnTextChanged="TextBox_TextChanged" TabIndex="3">

和一个事件处理程序

protected void TextBox_TextChanged(object sender, EventArgs e)
{
    WebControl changed_control = (WebControl)sender;

    var next_controls = from WebControl control in changed_control.Parent.Controls
                        where control.TabIndex > changed_control.TabIndex
                        orderby control.TabIndex
                        select control;

    next_controls.DefaultIfEmpty(changed_control).First().Focus();
}

此代码的含义是在页面回发后自动选择带有下一个TabIndex的TextBox（请参阅Little JB的问题）。实际上，我收到InvalidCastException，因为无法将其从System.Web.UI.LiteralControl（WebControl.Controls实际上包含LiteralControls）投射到System.Web.UI.WebControls.WebControl。

我有兴趣以某种方式修改此方法以接收有效的解决方案吗？谢谢！

Answer 1

类型

from control in changed_control
  .Parent
  .Controls
  .OfType<WebControl>()