Guest Book Solution You can also view part I of this article which describes the setting up of this application with Visual Studio 2008 and IIS 7, running on Vista. SQL Server 2005 was used as the database. I had originally blogged on this using VS 2005 but feedback indicated that quite a few people are now using VS 2008, so I upgraded it to VS 2008, which I am currently running on VMWare Workstation... the best $190 I ever spent. This is part II and the full code will be available for download in part III, real soon!

Speaking of feedback, I have been having problems with the comments system on this blog for some time now. So, pretty soon I am upgrading the blog engine and switching to a database version. The plan is to eventually make it a real "Community" site. Watch this space...

The Guest Book application is written in C# and is pretty straightforward. Here I will walk through the creation of the back-end which will allow the site administrator to moderate the comments posted to the guest book by site visitors.

First, we need to set up our membership system. The membership system is where most people seem to get stuck. There are several ways of achieving the same thing and I think that this is what causes much of the confusion. Typically, in an application such as this you would use a CAPTCHA control to combat the spammers, so we are not going to force users to register in order to sign the guest book. We will need an administration area for our admin forms, so we will create an "admin" role. The way I go about this is to create a new folder and call it Admin. Add a config file  to this new folder and set up the authorization rules as shown below.

Admin Web.config

Now, we're going to cheat a little. I'm going to do the TV chef and slip in a little something I pre-prepared earlier in the kitchen (actually gleaned from several of Scott Guthrie's blog postings). I always keep a sample Web.config file handy that I know is set up correctly for a basic membership system. I start this way rather than jumping in right off with the WSAT wizard because I want to have one single database for both my application and membership data. Tidier. So, I manually set up the database connection in the project Web.config file, along with entries for the membership and authentication sections. See the snippets below, and don't forget to include the roleManager tag!

Project Web.config

Now that the membership database connection is configured the way we want it, we can run the aspnet_regsql tool from the command line. This will create the actual membership database objects for us as part of our Guests database. Just navigate from the start menu to SQL Server Management Studio and locate the command line tool under the Configuration Tools folder. Simply enter aspnet_regsql at the prompt and you will be presented with the SQL Server Setup Wizard. Here are some screenshots showing the correct selections to make:

SQL Server Setup Wizard

SQL Server Setup Wizard

SQL Server Setup Wizard

If you go to SSMS and refresh the database, you should now be able to expand the tables icon, and you will see that the wizard had created everything we need for our membership system. At this stage, you are ready to run the WSAT tool and start setting up the admin role and adding the admin user. I will outline this process in the final installment, as well as the creation of our administration forms. Stay tuned!

Membership Database Objects

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Events and Delegates - Part II

by agrace 8. September 2007 09:24

Hungry Geek You can read part one of this topic here. This part presents a simple example of how to publish and subscribe to an event that does not send data. Note that events such as button clicks, that generate no data can avail of the EventHandler delegate provided in the class library.

Publish an Event - Five Steps:

* Define type inherited from EventArgs to contain any event-related data. If there is no data, use pre-defined EventArgs type

* Define delegate that specifies prototype of event handler. If the events generates no data, use pre-defined EventHandler delegate

* Define an event based on the delegate type

* Define a protected, virtual method to raise the event

* When the event occurs, call the protected, virtual method above

class ButtonPublisher
{
     public delegate void EventHandler(object sender, EventArgs e);
     public event EventHandler Click;

     // Each class that publishes an event provides a
     // protected, virtual method to raise that event.
     // The "On" name prefix makes this easy to spot.
     protected void OnClick()
     {
         // Check for subscibers
         if (Click != null)
             // Notify them
             Click(this, null);
     }

     // Raise the event
     public void PerformClick()
     {
         OnClick();
     }
}

 

Subscribe to an Event - Three Steps:

* Implement an event handler with same signature specified by the event's delegate object

* Create a delegate object specified for the event. This delegate refers to the event handler method (see below)

this.Click += new EventHandler(ButtonClick_Handler);

 

* Subscribe to event by attaching event handler to the event (see above). Use the += operator so as not to cancel any previously registered delegates

class Subscriber
 {
     static void Main(string[] args)
     {
         ButtonPublisher button = new ButtonPublisher();
         // Create new delegate object and subscribe to event
         button.Click += new ButtonPublisher.EventHandler(ButtonClick_Handler);
         button.PerformClick();
     }

     static public void ButtonClick_Handler(object sender, EventArgs e)
     {
         Console.WriteLine("Button Clicked");

         // Keep console window open long enough to read!
         System.Threading.Thread.Sleep(10000);
     }
 }

 

Happy coding!

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Events and Delegates - Part I

by agrace 1. September 2007 09:46

This is part one of a series of posts on events and delegates, a powerful means of implementing loosely-coupled designs. This part will focus on delegates. You can read part two here.

Introduction

As a developer, I think it took me longer than necessary to get my head around the code details of the event/delegate paradigm. In retrospect, I believe this was mainly due to my lack of understanding of the delegate type, which connects everything together.

Another problem I encountered was a lack of consistency of language and definitions used by the authors of books and articles on events and delegates. More on this later.

Publishers + Subscribers = Observer Pattern

 

There is no need to have a PhD in anonymous methods, function pointers, multicast versus single cast delegates and the like, in order to get started with events. What you do need is a basic understanding of the central piece of the jigsaw: the delegate. Next, you need to get an overview of the Publish-Subscribe model. Finally, you need to open up your code editor and create a basic event sample for yourself.

Overview

Generally, delegates (or callbacks) are typesafe pointers to methods, similar to function pointers in C++. We can use delegates to specify callbacks and also to register handlers for GUI events like button clicks. Unlike function pointers, which can only contain the address of a static method, a delegate can refer to instance methods in classes - this is what makes them tremendously useful. A delegate is like an interface: the difference is that the delegate declares a single static or reference method, whereas the interface can declare several methods. Whenever we want classes to communicate with less coupling than with an interface, we should use a delegate. In other words, delegates are not only for use with events!

If we need to specify an action or method in advance and we don't know which method, or even object, that will perform this action, we should use a delegate. For example, we can connect a button to a delegate and at runtime we can resolve that delegate to a particular method to be run.

Delegates

A delegate is a special type in .NET whose main role in life is to hold a reference to a method. Delegates are defined with a signature, much like methods, and can only hold a reference to a method which matches this signature. We declare a delegate by using the "delegate" keyword and specifying the signature of the method to which it holds a reference. The following is a declaration of a delegate that can reference a method that takes two parameters and does not return a value:

public delegate void EventHandler(object sender, EventArgs e);

 

The delegate is a TYPE; think of the entire statement above as a type. A method matching this signature would look like this:

public void Button_Clicked(object sender, EventArgs e);

 

In the following example, the delegate called SampleDelegate can invoke any method that is passed a string parameter and returns an int:

delegate int SampleDelegate(sting str);

 

We can now initialize a new delegate, like so...

SampleDelegate del = new SampleDelegate(DoSomething);

 

 ... and can call the delegate as follows:

del(someString);

 

Terminology

A final point regarding terminology. When we talk about classes, we use two separate terms: class and object. With delegates, there is only a single term. An instance of a delegate class is also known as a delegate. So, we need to pay attention to context here. I will come back to the issue of terminology in the next post which will focus on events.

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