lunes, 21 de septiembre de 2009

ASP.NET AJAX en 10 minutos (Introducción)


¿Qué es AJAX?

Acrónimo de Asynchronous JavaScript And XML.

No es otra cosa que la combinación de varias tecnologías existentes para el desarrollo de aplicaciones web interactivas:

  • XMLHttpRequest
  • JavaScript
  • Document Object Model
  • XML y XSLT

La experiencia de navegación del usuario será mucho más rica. Ya no se refrescará la página constantemente al interactuar con ella.

Veamos un ejemplo sencillo que nos muestre el potencial de ASP.NET AJAX. Con esto podremos ver los principales controles de esta tecnología.

ASP.NET AJAX Ejemplo Práctico

En el ejemplo que trataremos insertaremos una grilla con información de los empleados que se encuentra en un archivo XML, y habilitaremos el paginado del grid, y como lo haremos usando AJAX, pues al paginar no se recargará toda la página.

1. Lo primero que haremos será crear el proyecto de ASP.NET. En mi caso estoy usando VS 2008. Si estas usando VS 2005 debes tener instalada las extensiones de Microsoft ASP .Net 2.0 AJAX Extensions 1.0 y deberás escoger la plantilla de proyecto ASP.NET AJAX Enabled Web Site.

2. Después de creado el proyecto, crearemos una nueva página web (Web Form) a la cual llamaremos Empleados.aspx

3. Agregaremos entonces a dicha página 2 controles:

· ScriptManager: Se encarga del trabajo con el cliente.

· UpdatePanel: Dentro de este contenedor colocaremos todos los controles que deseamos se envíen al servidor sin necesidad de recargar la pagina completamente.

4. Es este punto colocaremos dentro del UpdatePanel los controles deseados, en nuestro caso de ejemplo una grilla (GridView) a la cual llamaremos grdEmpleados.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Empleados.aspx.cs" Inherits="Ajax.Empleados" %>
<html xmlns="" >
<head runat="server">
  <title>Ejemplo Básico de Ajax</title>
  <form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <asp:GridView ID="grdEmpleados" runat="server" AllowPaging="True"
          AutoGenerateColumns="False" DataSourceID="XmlDataSource1" >
            <asp:BoundField DataField="IDEmpleado" HeaderText="IDEmpleado" />
            <asp:BoundField DataField="Nombre" HeaderText="Nombre" />
            <asp:BoundField DataField="Apellidos" HeaderText="Apellidos" />
    <%--Los Datos--%>
    <asp:XmlDataSource ID="XmlDataSource1" runat="server"
    <asp:XmlDataSource ID="XmlDataEmpleados"  runat="server"></asp:XmlDataSource>       


Esta grilla (Grid grdEmpleados) se nutre o se carga desde un fichero Empleados.xml y configuramos la grilla para que habilite el paginado. El resultado sería este:

ASP.NET AJAX 1.0 Ejemplo

Como se observa en la imagen, hemos creado un grid con paginado, pero lo interesante es que al movernos entre las paginas, no se recarga toda la página, solo los datos de la grilla.


Adicionar AJAX a nuestras aplicaciones ASP.NET es muy fácil, y el resultado es bien satisfactorio a la experiencia del usuario. Solo es cuestión de incluir un ScriptManager y un objeto UpdatePanel -ContentTemplate dentro del cual colocaremos los objetos que queremos se refresquen sin necesidad de recargar toda la página.

Pero hasta aquí solo hemos rallado la pintura del uso de ASP.NET AJAX, hay otros controles bien interesantes como es el caso del UpdateProgress, Timer. También tenemos otra interesante colección de componentes  ASP.NET AJAX Control Toolkit con la que podremos obtener interesantes efectos con la inclusión de unas pocas líneas en nuestros proyectos.

NOTA: Hasta aquí hemos comentado algunas de las ventajas, pero también debemos tener en cuenta algunas limitaciones o cuestiones en el uso de Ajax, en otro artículo intentaré comentarlas.

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