ASPxClientCallbackPanel.BeginCallback Event

Occurs when a callback for server-side processing is initiated.

Declaration

BeginCallback: ASPxClientEvent<ASPxClientBeginCallbackEventHandler<ASPxClientCallbackPanel>>

Event Data

The BeginCallback event's data class is ASPxClientBeginCallbackEventArgs. The following properties provide information specific to this event:

Property	Description
command	Gets a command name that identifies which client action forced a callback to occur.

Remarks

The BeginCallback and ASPxClientCallbackPanel.EndCallback events can be used to perform specific client-side actions (for example, to display and hide an explanatory text or picture) while a callback is being processed on the server side.

Example

The ASPxCallbackPanel control provides a built-in loading panel, however you can implement a custom one. For this purpose, the default panel is hidden by setting the SettingsLoadingPanel.Enabled property to false. The custom panel is implemented using the ASPxLoadingPanel control. The callback panel’s ASPxClientCallbackPanel.BeginCallback and ASPxClientCallbackPanel.EndCallback client-side events are used to show and hide the loading panel respectively. Additionally, this example demonstrates how to add, modify, and hide controls in the ASPxCallbackPanel control in the ASPxCallbackPanel.Callback event handler.

Note

A complete sample project is available at https://github.com/DevExpress-Examples/how-to-implement-a-custom-loading-panel-for-the-aspxcallbackpanel-control-t228855

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<%@ Register Assembly="DevExpress.Web.v14.2, Version=14.2.6.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" Namespace="DevExpress.Web" TagPrefix="dx" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>How to implement a custom loading panel, and how to add and hide controls in the ASPxCallbackPanel control</title>
    <style>
        .sendCommentBlock {
            margin: 20px 0;
        }

        .comment {
            border-bottom: 1px dashed #888888;
        }
    </style>
    <script>
        function SendCommentCallback(s, e) {
            CallbackPanel.PerformCallback();
        };

        function OnBeginCallback(s, e) {
            LoadingPanel.Show();
        };

        function OnEndCallback(s, e) {
            LoadingPanel.Hide();
        };
    </script>
</head>
<body>
    <form id="form1" runat="server">
        <div class="sendCommentBlock">
            <dx:ASPxButton ID="Button" runat="server" Text="Post Comment" AutoPostBack="false">
                <ClientSideEvents Click="SendCommentCallback" />
            </dx:ASPxButton> 
            <br />
            <br />
            <dx:ASPxTextBox ID="TextBox" runat="server" Width="170px"></dx:ASPxTextBox>
        </div>

        <dx:ASPxCallbackPanel ID="CallbackPanel" ClientInstanceName="CallbackPanel" 
            runat="server"
            CssClass="pnl"
            Width="300px"
            OnCallback="CallbackPanel_Callback"
            OnInit="CallbackPanel_Init">
            <SettingsLoadingPanel Enabled="false" />
            <ClientSideEvents BeginCallback="OnBeginCallback" EndCallback="OnEndCallback" />
            <PanelCollection>
                <dx:PanelContent>
                    <dx:ASPxLabel ID="CountLabel" runat="server" Text="Comments Count : "></dx:ASPxLabel>
                    <br />
                    <br />
                    <dx:ASPxLabel ID="NoCommentsLabel" runat="server" Text="No Comments" ForeColor="Gray"></dx:ASPxLabel>
                </dx:PanelContent>
            </PanelCollection>
        </dx:ASPxCallbackPanel>

        <dx:ASPxLoadingPanel ID="LoadingPanel" ClientInstanceName="LoadingPanel"
            runat="server"
            Modal="true"
            HorizontalAlign="Center"
            VerticalAlign="Middle">
            <Image Url="Images/load.gif" Height="50px" Width="50px"></Image>
        </dx:ASPxLoadingPanel>
    </form>
</body>
</html>

using System;
using System.Collections.Generic;
using System.Threading;
using DevExpress.Web;

public partial class _Default : System.Web.UI.Page {
    protected void CallbackPanel_Callback(object sender, DevExpress.Web.CallbackEventArgsBase e) {
        ASPxCallbackPanel panel = (ASPxCallbackPanel)sender;
        NoCommentsLabel.Visible = false;
        Thread.Sleep(3000);

        ASPxLabel comment = new ASPxLabel() {
            Text = string.Format("[{0}]\n{1}\n\n",
                DateTime.Now.ToLocalTime(),
                !string.IsNullOrEmpty(TextBox.Text) ? TextBox.Text : "Empty comment"
            ),
            CssClass = "comment"
        };

        List<ASPxLabel> comments = (List<ASPxLabel>)Session["comments"] ?? new List<ASPxLabel>();

        comments.Add(comment);
        panel.Controls.Add(comment);
        Session["comments"] = comments;

        CountLabel.Text = "Comments Count : " + comments.Count;
    }

    protected void CallbackPanel_Init(object sender, EventArgs e) {
        if(!IsPostBack && !IsCallback)
            Session.Clear();
        RecreateComments(sender);
    }

    private void RecreateComments(object sender) {
        List<ASPxLabel> comments;
        if((comments = (List<ASPxLabel>)Session["comments"]) != null) {
            CountLabel.Text = "Comments Count : " + comments.Count;
            ASPxCallbackPanel panel = (ASPxCallbackPanel)sender;
            NoCommentsLabel.Visible = false;
            foreach(ASPxLabel comment in comments) {
                panel.Controls.Add(comment);
            }
        }
    }
}

Imports System
Imports System.Drawing
Imports System.Threading
Imports DevExpress.Web

Partial Public Class _Default
    Inherits System.Web.UI.Page

    Protected Sub ASPxCallbackPanel1_Callback(ByVal sender As Object, ByVal e As DevExpress.Web.CallbackEventArgsBase)
        Dim panel As ASPxCallbackPanel = DirectCast(sender, ASPxCallbackPanel)

        ' Perform long task
        Thread.Sleep(5000)

        ' Add/Modify/Hide controls inside callback panel
        TimeLabel.Text = Date.Now.ToLongDateString()
        TimeLabel.ForeColor = Color.Green
        TextBoxToHide.Visible = False
        ButtonToDisable.Enabled = False

        panel.Controls.Add(New ASPxHyperLink() With {.NavigateUrl = "https://www.devexpress.com/sc", .Text = "Navigate to DevExpress support center"})
    End Sub
End Class

<%@ Page Language="vb" AutoEventWireup="true" CodeFile="Default.aspx.vb" Inherits="_Default" %>

<%@ Register Assembly="DevExpress.Web.v14.2, Version=14.2.6.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" Namespace="DevExpress.Web" TagPrefix="dx" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style>
        .btn-send {
            margin: 20px 0;
        }
    </style>
    <script>
        function SendTaskRequest(s, e) {
            panel.PerformCallback();
        };

        function BeginCallbackHandler(s, e) {
            console.debug(e)
            loadingPanel.Show();
        };

        function EndCallbackHandler(s, e) {
            loadingPanel.Hide();
        };
    </script>
</head>
<body>
    <form id="form1" runat="server">
        <dx:ASPxButton ID="ASPxButton1" runat="server" Text="Perform Task" AutoPostBack="false" CssClass="btn-send">
            <ClientSideEvents Click="SendTaskRequest" />
        </dx:ASPxButton>

        <dx:ASPxCallbackPanel ID="ASPxCallbackPanel1" runat="server"
            ClientInstanceName="panel"
            CssClass="pnl"
            Width="300px" 
            OnCallback="ASPxCallbackPanel1_Callback">
            <SettingsLoadingPanel Enabled="false" />
            <ClientSideEvents BeginCallback="BeginCallbackHandler" EndCallback="EndCallbackHandler" />
            <PanelCollection>
                <dx:PanelContent>
                    <dx:ASPxLabel ID="TimeLabel" runat="server" Text="[Server Time]" CssClass="margin-element"></dx:ASPxLabel>
                    <dx:ASPxTextBox ID="TextBoxToHide" runat="server" Width="170px" NullText="This textbox will be hidden"></dx:ASPxTextBox>
                    <dx:ASPxButton ID="ButtonToDisable" runat="server" Text="Button"></dx:ASPxButton>
                    <br />
                </dx:PanelContent>
            </PanelCollection>
        </dx:ASPxCallbackPanel>

        <dx:ASPxLoadingPanel ID="ASPxLoadingPanel1" runat="server" 
            ClientInstanceName="loadingPanel" 
            Modal="true" 
            HorizontalAlign="Center" 
            VerticalAlign="Middle">
            <Image Url="Images/load.gif" Height="50px" Width="50px"></Image>
        </dx:ASPxLoadingPanel>
    </form>
</body>
</html>

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ASPxClientCallbackPanel.BeginCallback Event

Declaration

Event Data

Remarks

Example