单击按钮时动态加载用户控件的问题 [英] Issue with dynamically loading a user control on button click

问题描述

我有一个页面，我在其中动态加载用户控件，如下所示:

I have a page in which I am loading a user control dynamically as follows:

Default.aspx:

    <cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </cc1:ToolkitScriptManager>

    <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>

Default.aspx.cs:

    protected void Page_Load(object sender, EventArgs e)
    {
        var ctrl = LoadControl("~/UserCtrl1.ascx");
        ctrl.ID = "ucUserCtrl1";
        PlaceHolder1.Controls.Add(ctrl);
    }

下面是UserCtrl1.ascx的代码

<asp:Label ID="Label1" runat="server"></asp:Label>
<asp:Button ID="Button1" runat="server" Text="Button1" OnClick="Button1_Click" />
<br />
<asp:PlaceHolder ID="PlaceHolder2" runat="server"></asp:PlaceHolder>

单击 Button1 时，我正在动态加载另一个用户控件

I am dynamically loading another user control when the Button1 is clicked

UserCtrl1.ascx.cs

    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = "UserControl - 1 button clicked!";

        var ctrl = LoadControl("~/UserCtrl2.ascx");
        ctrl.ID = "ucUserCtrl2";
        PlaceHolder2.Controls.Add(ctrl);
    }

下面是 UserCtrl2.ascx 的标记

Below is the markup for UserCtrl2.ascx

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <asp:Label ID="Label2" runat="server"></asp:Label>
        <asp:Button ID="Button2" runat="server" Text="Button2" OnClick="Button2_Click" />
    </ContentTemplate>
</asp:UpdatePanel>

UserCtrl2.ascx.cs

    protected void Button2_Click(object sender, EventArgs e)
    {
        Label2.Text = "UserControl - 2 button clicked!";
    }

当我单击 UserCtrl1 中的 Button1 时页面加载后，单击事件会触发，我可以看到 Label1 文本.它还正确加载了 UserCtrl2，但是当我单击 UserCtrl2 中的 Button2 时，单击事件会触发，更糟糕的是，当我单击 Button2 两次时，UserCtrl2 控件会从页面中消失.我怎样才能解决这个问题?

After the page loads when I click the Button1 in UserCtrl1 the click event fires and I am able to see the Label1 text. It also properly loads the UserCtrl2, but when I click the Button2 in UserCtrl2 the click event dosent fire and even worse when I click the Button2 twice the UserCtrl2 control dissappears from the page. How can I fix this?

推荐答案

第二个控件的问题是您只有在单击按钮 1 后才加载它.但是当其他一些(不是按钮 1 单击)回发发生时第二个控件未加载.

The problem with the second control is that you are loding it only after the click of button 1. But when some other (not button 1 click) postback happens your second control is not loaded.

一个可能的修复方法是保存一些标志(例如在 ViewState 中)，这将帮助您确定是否应该加载第二个控件(并在页面加载时加载).

One of possible fixes is saving some flag (e.g. in ViewState) that will help you to determine if your second control should be loaded (and load in on page load).

protected void Button1_Click(object sender, EventArgs e)
{
    Label1.Text = "UserControl - 1 button clicked!";

    var ctrl = LoadControl("~/UserCtrl2.ascx");
    ctrl.ID = "ucUserCtrl2";
    PlaceHolder2.Controls.Add(ctrl);

    this.SecondControlLoaded = true; // This flag saves to ViewState that your control was loaded.
}

protected void Page_Load(object sender, EventArgs e)
{
    var ctrl = LoadControl("~/UserCtrl1.ascx");
    ctrl.ID = "ucUserCtrl1";
    PlaceHolder1.Controls.Add(ctrl);

    if (this.SecondControlLoaded)
    {
        var ctrl = LoadControl("~/UserCtrl2.ascx");
        ctrl.ID = "ucUserCtrl2";
        PlaceHolder2.Controls.Add(ctrl);
    }
}

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