Please Wait - Building a WaitScreen control for ASP.NET

Sometimes it happens that a form is processing and you need to make sure that the users don't panic and run away before it finishes. A splash screen with a "Loading..." indicator can help to calm down frightened users and make life easier for technical support staff. Back in the days of classic ASP (VBScript) which used a linear programming approach we had to start by setting the response buffer to true: This line does nothing but instructing the server NOT to send anything back to the client until the page has been finished processing. An exception can be forced by calling the flush command: Calling flush lets the server send everything to the client that is processed so far. This will also speed up your page since the server doesn't have to switch back and forth between executing the page and sending bits to the browser. Using this we were able to accomplish the following steps: Send e.g. a div-layer containing a "Loading..." graphic to the client Process the long running task. Send the results of the long running task to the client Send a client side script to the client, that hides the div-layer containing the "Loading..." graphic 1: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" ""> 2: <html xmlns=""> 3: ... 4: <body> 5: <div id="splashScreen"> 6: <img src="wait.gif" width="75" height="15" /> 7: </div> 8: <script type="text/javascript"></script> 9: </body> 10: </html> I haven’t mentioned yet that client side Javascript initially checks what kind of browser we have to deal with (either up level like Internet Explorer 7.0, other Internet Explorer’s or Netscape 4.x). But with ASP.NET we have got a complete different way of how the page is executed. Today we have a Page class, which has an event based execution model and controls – so how can this mechanisms be used in ASP.NET? The difference between classic ASP and ASP.NET, that initially seems to be a problem, is really an advantage. It gives us the ability to write and store our code in a more structured manor. This way we can separate infrastructure code form application logic code. It lets us focus on the things we, as application developers, really need to do – To get things done. First of all we need to do a few initial steps: · Start Visual Studio (or use notepad.exe) · Creating a new Project of the type “Class Library” (on skip this if you are using notepad) · Rename Class1.cs to WaitScreen.cs (or just save your file as WaitScreen.cs using notepad) · Add a reference to the namespace “System.Web” (or remember to add the compiler switch /r pointing to the assembly System.Web.dll) After our environment has been set up we can start writing the code. First we outline the class to use it as a WebControl by deriving it from the WebControl class. 1: using System; 2: using System.ComponentModel; 3: using System.Web.UI; 4: using System.Web.UI.WebControls; 5:  6: namespace devcoach.Web.UI.Controls 7: { 8: /// <summary> 9: /// The WaitScreen control displays a grafic while a long running operation 10: /// is running. 11: /// </summary> 12: public class WaitScreen : WebControl 13: { 14: } 15: } 16:  Controls are reusable components so it is important to let the client side developer (the guy who uses the control in Visual Web Developer – this might also be you…) the opportunities to customize the layout of the control. In our case the only customization that can be done would be a different graphic that is displayed during the long running operation is executed on the server. Here is the code that allows the client side developer to easily set a URL, pointing to an graphics file, form an attribute on the ServerContol or by directly setting the value of the property from the code behind. 1: // This field holds the URL pointing to an image 2: private string m_ImageUrl = "~/images/busy.gif"; The private field m_ImageUrl is initialized with a default image on the instantiation of the class so – if the image exists – the client side developer mustn’t explicitly set anything. 1: /// <summary> 2: /// Gets/sets the URL pointing to an image. 3: /// A string containing the URL pointing 4: /// to an image.. 5: /// This property gets/sets the URL pointing to an image. 6: /// </summary> 7: [Description("Gets/sets the URL pointing to an image.")] 8: public string ImageUrl 9: { 10: get { return m_ImageUrl; } 11: set { m_ImageUrl = value; } 12: } The property ImageUrl just gives public access to the private field m_ImageUrl. Having (again) the client side developer in mind we provide the XML comments summary, value and remarks and additionally set the description attribute, which allows Visual Studio to display details in the properties window. Delegates and events are one of the most powerful tools that come with .NET Framework and we can use them to let the client developer attach his/her custom long running operation as custom event handler code. Even more then one method can be attached so that all together are the “one long running task” that is processed while the graphic is displayed. Separated nicely from the infrastructure code (the control we are currently writing). Here is our event code: 1: public delegate void ProcessHandler(object sender, EventArgs e); 2:  3: public event ProcessHandler Process; The OnProcess method triggers the event and invokes the attached custom long running operations. Now that the ability is given that custom code can be executed using the event/delegate we need to actually raise the event and before that ensure that the response buffer is set to true and the graphic is send to the client. The load event of out control does this job for us. 1: /// <summary> 2: /// Triggers the Load event. 3: /// </summary> 4: protected override void OnLoad(EventArgs e) 5: { 6: base.OnLoad(e); 7:  8: Page.Response.Buffer = true; 9:  10: #region Show splash screen 11: Page.Response.Write("..."); 12: #endregion 13:  14: Page.Response.Flush(); 15:  16: OnProcess(); 17:  18: Page.Response.Flush(); 19:  20: #region Hide splash screen 21: Page.Response.Write("..."); 22: #endregion 23: } After OnProcess is called we call Flush like we did in classic ASP and send the piece of client side script to the client that will hide the div-layer containing the graphic indicating the user that something is happening. On the client side the control can now be used as follows in the *.aspx-Page: 1: <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %> 2: <%@ Register Assembly="devcoach.Web.WaitScreen" Namespace="devcoach.Web.UI.Controls" TagPrefix="ctrl" %> 3: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" ""> 4:  5: <html xmlns="" > 6: <head runat="server"> 7: <title>Untitled Page</title> 8: </head> 9:  10: <body> 11: <form id="form1" runat="server"> 12: <div> 13: 14: <ctrl:WaitScreen ID="WaitScreen" runat="server" OnProcess="WaitScreen_Process" /> 15: 16: </div> 17: </form> 18: </body> 19: </html> And the associated code behind page: 1: using System; 2: using System.Threading; 3: using System.Web.UI; 4:  5: public partial class _Default : Page 6: { 7: protected void WaitScreen_Process(object sender, EventArgs e) 8: { 9: // Put long running operation in here... 10: Thread.Sleep(4000); 11: } 12: } Design-time isn’t as easy as I would wish and therefore the functionality in this specific area is often kept short or even missing. One of the biggest problems is the missing HttpContext. Without it we cannot ask for example for the path of the current page, web environment variables, URL-parameters and so on… Our control is really a good example to show how we can add this kind of functionality because it is quite simple. The goal is to show the image set by the control default or the client side developer in the designer of Visual Web Developer. So we add a new class to our project and name it “WaitScreenDesigner.cs”. To access the built-in designer functionality we need to add reference to the “System.Design” assembly and a using declaration to the System.Web.UI.Design namespace on top of our control class. We also need to derive it from the ControlDesigner-class: 1: /// <summary> 2: /// The designer for the wait screen control. 3: /// </summary> 4: public class WaitScreenDesigner 5: : ControlDesigner 6: { 7: /// <summary> 8: /// Retrieves the HTML markup that is used to represent 9: /// the control at design time. 10: /// </summary> 11: /// <returns> 12: /// The HTML markup used to represent the control at design time. 13: /// </returns> 14: public override string GetDesignTimeHtml() 15: { 16: ... 17: } 18: } The designer of Visual Web Developer calls the method GetDesgnTimeHtml on the base class to generate the Html to display – If we override that method we can control what the designer shoes to the client side developer of our controls. To display the defined image we need to access the property of our control from the designer’s class’s method. Visual Studio’s extensibility API’s enable us to cast form the Component property of the designer to our control and easily read values of properties. The following example gets the value of the control’s class property ImageUrl: 1: string imageUrl = ((WaitScreen)this.Component).ImageUrl; Now that we have the set path to an image we should be able to display the image in an <img>-Tag except the URL contains the useful „~/“, which tells ASP.NET that the path starts with the root path of the current application. To translate such an URL to a physical path that we can use we need an instance of the web application – as the control this can be achieved though casting with the Component property of the designer. 1: IWebApplication webApp = 2: (IWebApplication)Component.Site.GetService( 3: typeof(IWebApplication)); The next step is to find the image as project item of our web project. The IWebApplication interface provides the method GetProjectItemFromUrl, which fits our needs. 1: IProjectItem item = webApp.GetProjectItemFromUrl(imageUrl); On the interface IProjectItem we will now find a property called PhysicalPath that we can use as value for the src attribute of an <img>-Tag, which will be returned form the GetDesignTimeHtml method: 1: return string.Concat( 2: "<img src=\"", 3: item.PhysicalPath, 4: "\" alt=\"Please wait...\" />"); Now its time to tell the Designer that our control should be rendered with our designer class we just created. This is done by assigning the DesignerAttribute to the control class. 1: [Designer(typeof(WaitScreenDesigner))] 2: public class WaitScreen : WebControl 3: { 4: ... 5: } If you now look at the designer the page should look like the following screenshot: To make it even more comfortable the control can be add to the Toolbox. But if you don’t want your control to be displayed as the “default 3rd party control grind” we still have one job to do. Add a 16x16 pixel icon file names WaitScreen.ico to the root of the project as embedded resource. And add the following attribute to the control class: 1: [ToolboxBitmap( 2: typeof(WaitScreen), 3: "devcoach.Web.UI.Controls.WaitScreen.ico")] 4: public class WaitScreen : WebControl 5: { 6: ... 7: } The long name is in the format {default_namespace_of_project}.{filename_and_ext} just in case you wonder where the devcoach.Web.UI.Controls.” comes from. Now you’ll see your icon instead of the “default 3rd party control grind”. Download

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Lennybacon says #1: Exceptions and ValidatorControls

I often get asked things through my messenger and today I decided to start sharing a few lines of the conversations...    Frank: Is there a way to connect a Validator to an Exception so that the validation summary can be used to display the exception message? Lennybacon says: 1. build a Custom Validator Frank: Ok Lennybacon says: 2. Use Page_Error or catch to set a "flag" to the Validator Lennybacon says: 3. override the method EvaluateIsValid and return the state of the flag Lennybacon says: This way the validator (if called on the postback) indicates its validation as true and after the flag is set false. Lennybacon says: Here is some pseudo-code Lennybacon says:        try        {          CriticalOperation();        }        catch(MyException e)        {          MyValidator.SetInvalid();          MyValidator.ErrorMessage = "bla bla: " + e.Message;          Page.Validate();        } Lennybacon says:        Validator : CustomValidator        {           bool flag = true;           void setInvalid(){flag=false;}           bool EvulateIsValid()           {                return flag;           }        }

Executing CREATE statements from within Visual Studio 2005

If you try to run a CREATE statement in a query (right click on a database in the Server Explorer) you receive this message. So i wrote a small utility which will do the job for me. using System; using System.IO; using System.Data.SqlClient; using System.Collections.Generic; using System.Text; using System.Windows.Forms;   namespace MdfExec {     class Program     {         static void Main(string[] args)         {             string _cnStr;               if (args.Length == 2)             {                 _cnStr =                     "data source=.\\SQLEXPRESS;Integrated Security=SSPI;" +                     "AttachDBFilename=" + args[1] + ";User Instance=true;";             }             else             {                 OpenFileDialog fd = new OpenFileDialog();                   fd.AddExtension = true;                 fd.DefaultExt = ".mdf";                 fd.ShowDialog();                   _cnStr =                     "data source=.\\SQLEXPRESS;Integrated Security=SSPI;" +                     "AttachDBFilename=" + fd.FileName + ";User Instance=true;";             }               using (SqlConnection _cn = new SqlConnection(_cnStr))             {             using(SqlCommand _cmd = _cn.CreateCommand())                    {                     using (StreamReader fs = File.OpenText(args[0]))                     {                         _cmd.CommandText = fs.ReadToEnd();                         _cmd.Connection.Open();                         _cmd.ExecuteNonQuery();                     }                    }             }         }     } }   You can now right click on a *.sql file choose "open with ..." and select MdfExec.exe to execute the SQL statement. Since there is no second parameter (but needed to define to which database to connect) a OpenFileDialog will prompt:   Happy coding

Customizing the Prop Snippet

I'm quite busy with a project I'm on with Clemens (the last before he'll join the Indigo team at Microsoft) - just to explain why it got bit quiet around me :-) Here is a modified version of the prop snippet that I want to share ( and remember :-P ). <?xml version="1.0" encoding="utf-8" ?> <CodeSnippets  xmlns="">       <CodeSnippet Format="1.0.0">             <Header>                   <Title>prop</Title>                   <Shortcut>prop</Shortcut>                   <Description>Code snippet for property and                   backing field</Description>                   <Author>Microsoft Corporation</Author>                   <SnippetTypes>                         <SnippetType>Expansion</SnippetType>                   </SnippetTypes>             </Header>             <Snippet>                   <Declarations>                         <Literal>                              <ID>type</ID>                               <ToolTip>Property type</ToolTip>                              <Default>int</Default>                         </Literal>                         <Literal>                              <ID>property</ID>                              <ToolTip>Property name</ToolTip>                              <Default>MyProperty</Default>                         </Literal>                         <Literal>                              <ID>field</ID>                              <ToolTip>The variable backing this                              property</ToolTip>                              <Default>myVar</Default>                         </Literal>                   </Declarations>                   <Code Language="csharp"><![CDATA[#region $property$             // This field holds the $property$       private $type$ $field$;         /// <summary>Gets/sets the $property$.</summary>       /// <value>A <see cref="$type$">$type$</see>       /// containing the $property$.</value>       /// <remarks>This property gets/sets the $property$.</remarks>       [System.ComponentModel.Description("Gets/sets the $property$.")]       public $type$ $property$       {             get { return $field$;}             set { $field$ = value;}       }       #endregion       $end$]]>                   </Code>             </Snippet>       </CodeSnippet> </CodeSnippets>

Complex Databinding

I just finished writing some ASP.NET code where I also typed the following lines:  <ItemTemplate> <asp:Image ID="IsOnline" runat="server" ImageUrl='<%# GetImageUrl((MembershipUser)Container.DataItem) %>' /> </ItemTemplate> ... protected string GetImageUrl(MembershipUser user) { if (user.IsLockedOut) { return "~/images/BadUser.gif"; } else if (!user.IsApproved) { return "~/images/GreyUser.gif"; } else if (user.IsOnline) { return "~/images/OnlineUser.gif"; } else { return "~/images/OfflineUser.gif"; } } Before I shutdown my machine I fetchted Mail and Feeds when i ran accross this posting by ScottGu pointing to Fritz Onions Blog. ;-)

Friday Night Andreas Hoffmann 2nd Lead Of The VfLNiederRhein User Group Picked Me Up Ad We Drove The Long Way Down To The

Friday night Andreas Hoffmann (2nd lead of the VfL-NiederRhein user group) picked me up ad we drove the long way down to the south.   Our destination for Saturday morning was the “Chaostage” event of the .NET user group Deggendorf  ( I had a session “Introducing the concepts and architecture of ASP.NET“ in the morning and a second one “Hello WebServices – Message-Oriented Programming for distributed systems” in the evening. We checked in at our hotel in Garching (I won’t tell the name but I’ll tell you a bit about the worst service). Because the waitress served me frozen potatoes with my steak I stood up and walked over to the bar. Just in this moment a voice behind me asked “Is this a codezone keychain? Are you gonna be at Microsoft on Monday?” It was Nicki Wruck ( the organizer of the ICE 2005 Community together with Frank Solinske ( IT-Pro Security Guru. Only one nano-second later we drank the first beer together. The geek meet was so exciting that I was just about to forget the bad service of our hotel J Sunday we fetched Stephan Oetzel ( in Poing. We picked up Michael Willers ( Developer Security Guru from the Airport to merge the Security guys in the “Hofbräukeller”. Uwe Baumann ( discussed about technical stuff with Andreas and me meanwhile. Later Nicki joined us together with Nico Lüdemann ( and Carola Helfert ( Monday - Launch Day – started with the Community GetTogether. Stephan and Andreas and I presented the results of the .NET Summit NRW (our community event). As always the time to do some “networking” was toooooooo short - even if we had at least the day before to talk to a few guys. The Launch Party was great. Steve Balmer’s Launch talk was transmitted per satellite into the Lobby of Microsoft in Germany – Great. The only problem again: So many people and such a small amount of time :-) 

Code like i want to see it with ASP.NET 2.0

A short statement additional to my post against the spagetti code because I think Scott got me wrong: The Object Data Source is one of the coolest things out there cause it's never been so easy to use n-tier applications and bind custom business objects to databound controls. And this is exactly what I tell the folks out there in my articles and talks.