ASP.Net Controls 用法大全 【转载】

<asp:DataGrid id=DataGrid1 runat="server" DataSource="<%# employees1 %>"
       AutoGenerateColumns="False" ShowFooter="True">
  <Columns> 
    <asp:BoundColumn DataField="emp_id" SortExpression="emp_id" HeaderText="emp_id"/>
    <asp:BoundColumn DataField="fname" SortExpression="fname" HeaderText="fname"/>
    <asp:BoundColumn DataField="lname" SortExpression="lname" HeaderText="lname"/>
    <asp:TemplateColumn>
      <HeaderTemplate>
        <asp:DropDownList Runat="server" ID="DropDownList1">
          <asp:ListItem Value="1">One</asp:ListItem>
          <asp:ListItem Value="2">Two</asp:ListItem>
          <asp:ListItem Value="3">Three</asp:ListItem>
        </asp:DropDownList>
      </HeaderTemplate>
      <ItemTemplate>
        <asp:TextBox Runat="server" ID="TextBox1" />
      </ItemTemplate>
      <FooterTemplate>
        <asp:DropDownList Runat="server" ID="Dropdownlist1">
          <asp:ListItem Value="1">One</asp:ListItem>
          <asp:ListItem Value="2">Two</asp:ListItem>
          <asp:ListItem Value="3">Three</asp:ListItem>
        </asp:DropDownList>
      </FooterTemplate>
    </asp:TemplateColumn>
    <asp:ButtonColumn Text="Select" CommandName="Select"></asp:ButtonColumn>
  </Columns>
</asp:DataGrid>

private void DataGrid1_SelectedIndexChanged(object sender, System.EventArgs e)
{
   DropDownList d;                 
   d = DataGrid1.Controls[0].Controls[0].FindControl("DropDownList1") as DropDownList;
   if(d != null)
   {
      Response.Write("Found header DropDownList1 in SelectedIndexChanged event<br>");
   }
   int footerIndex = DataGrid1.Controls[0].Controls.Count-1;
   d = DataGrid1.Controls[0].Controls[footerIndex].FindControl("DropDownList1") as DropDownList;
   if(d != null)
   {
      Response.Write("Found footer DropDownList1 in SelectedIndexChanged event<br>");
      Response.Write(FindUtil.DumpParents(d));
   }
}

will give us both DropDownList controls in the header and footer, and produce the following output. Seeing hard coded index values into the Controls collection is a bit worrisome. If your control changes, or the DataGrid control changes in a newer version of the framework, this code could break. An alternate solution could involve looping through the DataGridTable controls looking for DataGridItem objects with a ItemType property equal to ListItem.Header or ListItem.Footer. Whichever you decide, neither feels extremely robust in the face of future changes.

FindControl in Repeater controls

Like the DataGrid, the Repeater is an INamingContainer. Let’s take a look at the following form which displays authors from SQL Server.

<asp:Repeater id="Repeater1" runat="server">
  <ItemTemplate>
     <tr>
        <td><%#DataBinder.Eval(Container.DataItem, "au_id")%></td>
        <td><%#DataBinder.Eval(Container.DataItem, "au_lname")%></td>
        <td><%#DataBinder.Eval(Container.DataItem, "au_fname")%></td>
        <td><asp:TextBox Runat="server" ID="TextBox1" /></td>
        <td><asp:Button Runat="server" ID="Button1" OnClick="Button1_Click" Text="Click" /></td>
     </tr>
  </ItemTemplate>
</asp:Repeater>

Each row of the repeater will contain a TextBox and Button control. Every Button control will use the same event handler where we can grab the corresponding TextBox control in the row with the following code.

protected void Button1_Click(object sender, System.EventArgs e)
{
   Button btn = sender as Button;
   TextBox tb = btn.Parent.FindControl("TextBox1") as TextBox;
   if(tb != null)
   {
      Response.Write("Found TextBox1 in Button1_Click event<br>");
      Response.Write(FindUtil.DumpParents(tb));
   }
}

Here you can see we have taken a different tack by asking for the parent of the Button control which has fired the event handler. In the following screen shot, you can see the parent of the TextBox (and the Button) is a RepeaterItem control (which also implements INamingContainer). Thus the first TextBox appearing on the screen will have an unique ID of Repeater1:_ctl0:TextBox1. One more tip before we move to the last section. Suppose we added a second button at the bottom of the form with the repeater. When the user clicks this button we want to loop the repeater collecting the contents of each TextBox control from every row. You can accomplish this task with the following code.

private void Button2_Click(object sender, System.EventArgs e)
{
   foreach(RepeaterItem item in Repeater1.Items)
   {
      TextBox b = item.FindControl("TextBox1") as TextBox;
      Response.Write(b.Text + "<br>");                       
   }
}

User Controls

For the sake of completeness, let’s take a look at how FindControl works when a User Control (ascx) appears. Let’s through the following user control into a form.

<%@ Control Language="c#" 
  AutoEventWireup="false" 
  Codebehind="MyUserControl.ascx.cs" 
  Inherits="aspnet.FindControls.MyUserControl" 
  TargetSchema="http://schemas.microsoft.com/intellisense/ie5"
%>
<asp:TextBox id="TextBox1" runat="server"></asp:TextBox>
<asp:Button id="Button1" runat="server" Text="Button"></asp:Button>

If we view the HTML output, we will see the following.

   <input name="MyUserControl1:TextBox1" type="text" id="MyUserControl1_TextBox1" />
   <input type="submit" name="MyUserControl1:Button1" value="Button" id="MyUserControl1_Button1" />

Although user controls do not implement INamingContainer, they do ensure their child controls will not have a naming conflict. For instance, if we placed two of these user controls on the same form, without munging the names we would have two TextBox1 controls on the same form. Although you generally will not need to do this, you can find a control from the code behind of a user control as easily as the first example in this article

private void Button1_Click(object sender, System.EventArgs e)
{
   TextBox b = this.FindControl("TextBox1") as TextBox;
   if(b != null)
   {
      Response.Write("Found TextBox1 on User Control Button1_Click<br>");
   }               
}

If you wanted to find the TextBox control from inside of the parent page (not recommended, but here for completeness), you would have to invoke FindControl on the user control. In the following example, we will also use FindControl to find our user control.

private void Page_Load(object sender, System.EventArgs e)
{
   MyUserControl u = FindControl("MyUserControl1") as MyUserControl;
   TextBox b = u.FindControl("TextBox1") as TextBox;
   if(b != null)
   {
      Response.Write("Found TextBox1 on Page_Load<br>");
   }                            
}

Conclusion

Hopefully this article has shed some light and will offer some assistance to those readers who have lost wayward controls. The behavior of FindControl makes perfect sense once you understand the purpose of INamingContainer and begin using FindControl on the correct objects.