 
<form id="form1" runat="server"> 
<asp:DropDownList ID="DropDownList1" runat="server"> 
<asp:ListItem>1</asp:ListItem> 
<asp:ListItem>2</asp:ListItem> 
<asp:ListItem>3</asp:ListItem> 
</asp:DropDownList> 
<asp:DropDownList ID="DropDownList2" runat="server"> 
<asp:ListItem>a</asp:ListItem> 
<asp:ListItem>b</asp:ListItem> 
<asp:ListItem>c</asp:ListItem> 
</asp:DropDownList> 
<asp:DropDownList ID="DropDownList3" runat="server"> 
<asp:ListItem>A</asp:ListItem> 
<asp:ListItem>B</asp:ListItem> 
</asp:DropDownList> 
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /> 
<asp:Panel ID="Panel1" runat="server"> 
</asp:Panel> 
<asp:Button ID="Button2" runat="server" Text="最后一個Button" /> 
</form> 

Test.aspx.cs關(guān)鍵代碼：

復(fù)制代碼代碼如下:

 
protected void Page_Load(object sender, EventArgs e) 
{ 
if (Session["Panel1"] != null) 
{ 
int index = this.Form.Controls.IndexOf(Panel1); 
this.Form.Controls.RemoveAt(index); 
Panel1 = Session["Panel1"] as Panel; 
this.Form.Controls.AddAt(index, Panel1); 
} 
} 
protected void Button1_Click(object sender, EventArgs e) 
{ 
for (int i = 0; i < 3; i++) 
{ 
Label label = new Label(); 
DropDownList ddl = this.FindControl("DropDownList" + (i + 1).ToString()) as DropDownList; 
label.Text = ddl.SelectedValue; 
Panel1.Controls.Add(label); 
} 
Literal br = new Literal(); 
br.Text = "<br/>"; 
Panel1.Controls.Add(br); 
Session["Panel1"] = Panel1; 
} 

當(dāng)頁面回發(fā)時，先記下Panel1在控件樹中的位置，并移除它，然后從Session變量獲取上次添加后的Panel1，并添加到控件樹中原來的位置，在這基礎(chǔ)上繼續(xù)添加新的Label控件。最后的那個Button是為了測試之用，作用有二：一是幫助查看添加的位置是否正確，二是用于檢測空回發(fā)時是否能維持上次的狀態(tài)。

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