An example of dynamically adding controls

There are 3 labels in the first click, 6 in the second click, and 9 in the third click, which means that you want to add 3 more in the last state for each click.
My method is to save the last state through Session. One solution is as follows:
Key Code:

Copy the codeThe code is as follows:

 
<form  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="last Button" />
</form> 

Key Code:

Copy the codeThe code is as follows:

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

When the page is posted back, first note the location of Panel1 in the control tree and remove it. Then get the last added Panel1 from the Session variable and add it to the original location in the control tree. On this basis, continue to add new Label controls. The last Button is for testing purposes, and has two functions: one is to help check whether the added position is correct, and the other is to detect whether the last state can be maintained when the empty postback is released.