一、C#中FindByValue函數的用法：
ListItem item = DropDownList1.Items.FindByValue(theme);
根據指定的值("theme")獲取 DropDownList 中對應的項。
二、FindControl的使用方法：
Control.FindControl (String)：在當前的命名容器中搜索帶指定 id 參數的服務器控件。（有點類似javascript中的getElementById(string)）
簡單的例子：
<form id="form1" runat="server">
<div>
<asp:TextBox ID="TextBox1" runat="server">TextBox</asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
<br />
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label></div>
</form>
如果需要獲得頁面中的"TextBox1",代碼中可以使用this.TextBox1來引用，這里我們使用FindControl:
protected void Button1_Click(object sender, EventArgs e)
{
//Control c = this.FindControl("TextBox1");
//TextBox tb= (TextBox)c;
//FindControl返回的是一個Control類型的控件，需要強制類型轉化成TextBox類型
TextBox tb=(TextBox)this.FindControl("TextBox1");
this.Label1.Text = tb.Text; }
當TextBox1放到其他控件里應該怎么查找呢？
<div>
<asp:Panel ID="Panel1" runat="server" Height="50px" ;125px">
<asp:TextBox ID="TextBox1" runat="server">TextBox</asp:TextBox>
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
</asp:Panel>
</div>
當TextBox1放到Panel里，似乎沒什么影響 TextBox tb=(TextBox)this.FindControl("TextBox1")，當查看生存頁
面的HTML代碼是發現，TextBox的ID並沒有改變，所以可以獲得TextBox1。
<div>
<div id="Panel1" style="height:50px;;">
<input name="TextBox1" type="text" value="TextBoxdsd" id="TextBox1" />
<span id="Label1">TextBoxdsd</span>
<input type="submit" name="Button1" value="Button" id="Button1" />
</div>
</div>
當TextBox1放到DataGrid中
<asp:DataGrid ID="dg1" runat="server" OnSelectedIndexChanged="dg1_SelectedIndexChanged">
<Columns>
<asp:TemplateColumn>
<ItemTemplate>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</ItemTemplate>
</asp:TemplateColumn>
<asp:ButtonColumn CommandName="Select" Text="選擇"></asp:ButtonColumn>
</Columns>
</asp:DataGrid>
這時候this.FindControl("TextBox1")==null,無法獲得TextBox1,查看生成頁面HTML發現，頁面有多個
<input name="dg1$ctl02$TextBox1" type="text" id="dg1_ctl02_TextBox1" />
<input name="dg1$ctl03$TextBox1" type="text" id="dg1_ctl03_TextBox1" />
TextBox1隱藏了，給DataGrid添加選擇列，通過以下方法獲得被選擇行的TextBox1
protected void dg1_SelectedIndexChanged(object sender, EventArgs e)
{
Control c = this.dg1.Items[this.dg1.SelectedIndex].FindControl("TextBox1");
//Control c = this.dg1.SelectedItem.FindControl("TextBox1");
TextBox tb = (TextBox)c;
tb.Text = "TextBox";
}
protected void dg1_EditCommand(object source, DataGridCommandEventArgs e)
{
TextBox tb = (TextBox)e.Item.FindControl("TextBox1");
this.Label1.Text = tb.Text.ToString();
}
如果是在DataGrid的頁眉和頁腳：
((TextBox)this.dg1.Controls[0].Controls[0].FindControl("TextBoxH")).Text = "Head";
((TextBox)this.dg1.Controls[0].Controls[this.dg1.Controls[0].Controls.Count - 1].FindControl
("TextBoxF")).Text = "Footer";
TextBox1在Repeater中
<asp:Repeater ID="Repeater1" runat="server" DataSourceID="SqlDataSource1"
OnItemCommand="Repeater1_ItemCommand">
<ItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" Text=""></asp:TextBox><%#DataBinder.Eval
(Container.DataItem,"ProductName")%><asp:Button ID="btn" OnClick="btn_click" runat="server"
Text="dddd" /><br />
</ItemTemplate>
</asp:Repeater>
通過按鈕來獲得TextBox1:
protected void btn_click(object sender, EventArgs e)
{
//獲得按鈕
Button btn = (Button)sender;
TextBox tb = (TextBox)btn.Parent.FindControl("TextBox1");
tb.Text = "Text";
}
或者
foreach (RepeaterItem item in this.Repeater1.Items)
{
((TextBox)item.FindControl("TextBox1")).Text = "Text2";
}
自定義控件里的TextBox1
<%@ Control Language="C#" AutoEventWireup="true" CodeFile="WebUserControl.ascx.cs"
Inherits="WebUserControl" %>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
引用<uc1:WebUserControl ID="WebUserControl1" runat="server" />
獲取TextBox1:
((TextBox)this.WebUserControl1.FindControl("TextBox1")).Text = "userc";
模板頁訪問頁面TextBox1
//模板頁的TextBox1
TextBox tbM = (TextBox)this.FindControl("TextBox1");
//頁面中的TextBox1
TextBox tbC = (TextBox)this.FindControl("ContentPlaceHolder1").FindControl("TextBox1");
tbC.Text = tbM.Text;
頁面使用模板頁的TextBox1
//模板頁的TextBox1
TextBox tbM = (TextBox)Master.FindControl("TextBox1");
//本頁面的TextBox1
//錯誤的方法：TextBox tbC = (TextBox)this.FindControl("TextBox1");
TextBox tbC = (TextBox)Master.FindControl("ContentPlaceHolder1").FindControl("TextBox1");
tbM.Text = tbC.Text.ToString();