在ASP.NET中添加動態控件

Question

在我看來，在ASP.NET Web窗體中動態添加控件存在固有的困難。 具體來說，要使動態添加的控件包含在ViewState ，並正確地Page_PreInit事件等，建議在Page_PreInit事件期間添加這些Page_PreInit 。

也就是說，很多時候我們可能想根據事件（例如用戶單擊按鈕）添加此類控件。 諸如Click事件之類的控件特定事件始終在Init之后甚至在Load之后運行。 假設以下.aspx ....

 <form id="form1" runat="server">
    <div>
      <asp:PlaceHolder ID="phAddresses" runat="server"></asp:PlaceHolder>
       <br /><br />
        <asp:Button ID="btnAddAddress" runat="server" Text="Add Another Address" OnClick="btnAddAddress_Click" />

...以及以下.aspx.cs ....

private static List<AddressUserControl> addresses = new List<AddressUserControl>();




protected void Page_PreInit(object sender, EventArgs e)
  {

   foreach (AddressUserControl aCntrl in addresses)
    {
      phAddresses.Controls.Add(aCntrl);
       // Helper to find button within user control
     addressButtonControl = findAddressControlRemoveButton(aCntrl);
     addressUserControlButton.ID = "btnRemoveAddress" + addressCount;
     addressUserControlButton.Click += new EventHandler(addressUserControlButton_Click);
     addressCount++;
    }
  }

 protected void btnAddAddress_Click(object sender, EventArgs e)
 {
  AddressUserControl aCntrl = LoadControl("~/UserControls/AddressUserControl.ascx")                 as    AddressUserControl;
 addresses.Add(aCntrl);
 }

現在，在上述情況下，顯示的用戶控件數始終落后於用戶實際添加的數量，因為Click事件要到PreInit之后才運行，在PreInit之后必須將控件添加到占位符。 我必須在這里遺漏一些東西，因為這似乎是ASP生命周期所固有的，並且需要一些“ hack”或其他。

編輯-是的，由於某些原因，我在btnAddress_Click（）期間添加的EventHandlers將無法運行，只有我在Page_Init期間或以聲明方式在標記中添加的EventHandlers無法運行。 這就是我試圖做的...

protected void btnAddAddress_Click(object sender, EventArgs e)
 {
   AddressUserControl aCntrl = LoadControl("~/UserControls/AddressUserControl.ascx") as AddressUserControl;
  addresses.Add(aCntrl);
  phAddresses.Controls.Add(aCntrl);
  findAddressControlRemoveButton(aCntrl);
  addressUserControlButton.ID = "btnRemoveAddress" + addresses.Count;

                ///////////////////////////////////////////////////////////////////////////////////
                // ADDED EVENT HANDLER HERE
                //////////////////////////////////////////////////////////////////////////////////////
  addressUserControlButton.Click += new E ventHandler(addressUserControlButton_Click);

  }

...但事件不會像我所說的那樣觸發。 有任何想法嗎？

編輯-這是我的AddressUserControl的標記。 文件背后的代碼中沒有邏輯

<%@ Control Language="C#" ClassName="AddressUserControl" AutoEventWireup="true" CodeBehind="AddressUserControl.ascx.cs" Inherits="XFAWithUserControl.UserControls.AddressUserControl" %>


    <asp:Panel ID="pnlAddressForm" runat="server">
        <asp:Label ID="lblStreet" runat="server" Text="Street Address"></asp:Label>
           <asp:TextBox ID="txtStreet" runat="server"></asp:TextBox>
             <br /><br />
            <asp:Label ID="lblCity" runat="server" Text="City"></asp:Label>
            <asp:TextBox ID="txtCity" runat="server"></asp:TextBox>
            <br /><br />
            <asp:Label ID="lblState" runat="server" Text="State"></asp:Label>
            <asp:TextBox ID="txtState" runat="server"></asp:TextBox>
            <br /><br />
            <asp:Label ID="lblZip" runat="server" Text="Zip"></asp:Label>
            <asp:TextBox ID="txtZip" runat="server"></asp:TextBox>
            <br /><br />
            <asp:Button ID="btnRemoveAddress" runat="server" Text="Remove Address" />
        </asp:Panel>

現在我對btnRemoveAddress的點擊事件只是這樣的愚蠢...

 private void addressUserControlButton_Click(object sender, EventArgs e)
  {
    Button thisButton = sender as Button;
    thisButton.Text = "Why Hello";
  }

但是我的目標是讓它刪除關聯的AddressUserControl，以便用戶可以通過單擊按鈕從頁面添加和/或刪除任意數量的AddressUserControls。

編輯-這是我現在所擁有的，仍然無法正常工作

protected void btnAddAddress_Click(object sender, EventArgs e)
        {
            AddressUserControl aCntrl = LoadControl("~/UserControls/AddressUserControl.ascx") as AddressUserControl;
            addresses.Add(aCntrl);
            phAddresses.Controls.Add(aCntrl);
            findAddressControlRemoveButton(aCntrl);
            addressUserControlButton.ID = "btnRemoveAddress" + addresses.Count;
            aCntrl.ChangeText += new EventHandler(addressUserControlButton_Click);
        }

private void addressUserControlButton_Click(object sender, EventArgs e)
{
    Button thisButton = sender as Button;
    thisButton.Text = "Why Hello";
}

AddressUserControl.ascx

<asp:Panel ID="pnlAddressForm" runat="server">
    <asp:Label ID="lblStreet" runat="server" Text="Street Address"></asp:Label>
    <asp:TextBox ID="txtStreet" runat="server"></asp:TextBox>
    <br /><br />
    <asp:Label ID="lblCity" runat="server" Text="City"></asp:Label>
    <asp:TextBox ID="txtCity" runat="server"></asp:TextBox>
    <br /><br />
    <asp:Label ID="lblState" runat="server" Text="State"></asp:Label>
    <asp:TextBox ID="txtState" runat="server"></asp:TextBox>
    <br /><br />
    <asp:Label ID="lblZip" runat="server" Text="Zip"></asp:Label>
    <asp:TextBox ID="txtZip" runat="server"></asp:TextBox>
    <br /><br />
    <asp:Button ID="btnRemoveAddress" runat="server" Text="Remove Address" OnClick="btnRemoveAddress_Click" />
</asp:Panel>

AddressUserControl.ascx.cs

public event EventHandler ChangeText;



   protected void Page_Load(object sender, EventArgs e)
    {

    }

    public void btnRemoveAddress_Click(object sender, EventArgs e)
    {
        if (this.ChangeText != null)
        {
            ChangeText(sender, e);
        }
    }

Answer 1

您需要將點擊處理程序中的邏輯添加到面板的Controls集合以及控件列表中，如下所示：

protected void btnAddAddress_Click(object sender, EventArgs e)
{
    AddressUserControl aCntrl = LoadControl("~/UserControls/AddressUserControl.ascx") as AddressUserControl;
    addresses.Add(aCntrl);
    phAddresses.Controls.Add(aCntrl);
}

更新：

在用戶控件中，您需要定義一個事件，該事件可以在承載用戶控件的頁面中定義，如下所示：

AddressUserControl.cs（代碼隱藏）：

public event EventHandler RemoveAddress;

protected void removeAddressUserControlButton_Click(object sender, EventArgs e)
{
    // Find out if the event has been set, if so then call it
    if (this.RemoveAddress!= null)
    {
        RemoveAddress(sender, e);
    }
}

現在，在您使用用戶控件的頁面上，執行以下操作：

// Wire up the user control's event
nameOfUserControl.RemoveAddress += new EventHandler(addressUserControlButton_Click);

最后，實現addressUserControlButton_Click事件：

protected void addressUserControlButton_Click(object sender, EventArgs e)
{
    // Do your dynamic control creation here or whatever else you want on the page
}