C#中FindByValue、FindControl函数的用法

一、C#中FindByValue函数的用法：
ListItem item = DropDownList1.Items.FindByValue(theme);
根据指定的值("theme")获取 DropDownList 中对应的项。
二、FindControl的使用方法：
Control.FindControl (String)：在当前的命名容器中搜索带指定 id 参数的服务器控件。（有点类似javascript中的getElementById(string)）
简单的例子：
<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>

如果需要获得页面中的"TextBox1",代码中可以使用this.TextBox1来引用，这里我们使用FindControl:

   protected void Button1_Click(object sender, EventArgs e)
    {
      //Control c = this.FindControl("TextBox1");
      //TextBox tb= (TextBox)c;
     //FindControl返回的是一个Control类型的控件，需要强制类型转化成TextBox类型
      TextBox tb=(TextBox)this.FindControl("TextBox1");
      this.Label1.Text = tb.Text;    }

当TextBox1放到其他控件里应该怎么查找呢？

   <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>

当TextBox1放到Panel里，似乎没什么影响 TextBox tb=(TextBox)this.FindControl("TextBox1")，当查看生存页

面的HTML代码是发现，TextBox的ID并没有改变，所以可以获得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>

当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="选择"></asp:ButtonColumn>
        </Columns>
        </asp:DataGrid>

这时候this.FindControl("TextBox1")==null,无法获得TextBox1,查看生成页面HTML发现，页面有多个
<input name="dg1$ctl02$TextBox1" type="text" id="dg1_ctl02_TextBox1" />
<input name="dg1$ctl03$TextBox1" type="text" id="dg1_ctl03_TextBox1" />
TextBox1隐藏了，给DataGrid添加选择列，通过以下方法获得被选择行的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的页眉和页脚：

((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>

通过按钮来获得TextBox1:

    protected void btn_click(object sender, EventArgs e)
    {
        //获得按钮
        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";
        }

自定义控件里的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" />

获取TextBox1:

((TextBox)this.WebUserControl1.FindControl("TextBox1")).Text = "userc";

模板页访问页面TextBox1

        //模板页的TextBox1
        TextBox tbM = (TextBox)this.FindControl("TextBox1");
        //页面中的TextBox1
        TextBox tbC = (TextBox)this.FindControl("ContentPlaceHolder1").FindControl("TextBox1");
        tbC.Text = tbM.Text;

页面使用模板页的TextBox1

        //模板页的TextBox1
        TextBox tbM = (TextBox)Master.FindControl("TextBox1");
        //本页面的TextBox1
        //错误的方法：TextBox tbC = (TextBox)this.FindControl("TextBox1");
        TextBox tbC = (TextBox)Master.FindControl("ContentPlaceHolder1").FindControl("TextBox1");
        tbM.Text = tbC.Text.ToString();