User and Custom Control

• The page parser parses the .ascx file specified in the Src attribute in the @ Register directive and generates a class that derives from the System.Web.UI.UserControl class.
• The parser then dynamically compiles the class into an assembly.
• If you are using Visual Studio, then at design time only, Visual Studio creates a code behind file for the user control, and the file is precompiled by the designer itself.
• Finally, the class for the user control, which is generated through the process of dynamic code generation and compilation, includes the code for the code behind file (.ascx.cs) as well as the code written inside the .ascx file.

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What are custom controls?

How to choose the base class for your custom control

• You should derive from System.Web.UI.Control if you want the control to render nonvisual elements. For example, and are examples of nonvisual rendering.
• You should derive from System.Web.UI.WebControls.WebControl if you want the control to render HTML that generates a visual interface on the client computer.

How to create and use a simple custom control that extends from System.Web.UI.Control using Visual Studio

1. Start Visual Studio.
2. Create a class library project, and give it a name, for example, CustomServerControlsLib.
3. Add a source file to the project, for example, SimpleServerControl.cs.
4. Include the reference of the System.Web namespace in the references section.
5. Check whether the following namespaces are included in the SimpleServerControl.cs file.

   System
   System.Collections
   System.ComponentModel
   System.Data
   System.Web
   System.Web.SessionState
   System.Web.UI
   System.Web.UI.WebControls
   

6. Inherit the SimpleServerControls class with the Control base class.

   public class SimpleServerControl : Control

7. Override the Render method to write the output to the output stream.

   protected override void Render(HtmlTextWriter writer) 
   {
    writer.Write("Hello World from custom control");
   }
   

   Note The HtmlTextWriter class has the functionality of writing HTML to a text stream. The Write method of the HtmlTextWriter class outputs the specified text to the HTTP response stream and is the same as the Response.Write method.
8. Compile the class library project. It will generate the DLL output.
9. Open an existing or create a new ASP.NET Web application project.
10. Add a Web Forms page where the custom control can be used.
11. Add a reference to the class library in the references section of the ASP.NET project.
12. Register the custom control on the Web Forms page.

    <%@ Register TagPrefix="CC " Namespace=" CustomServerControlsLib " Assembly="CustomServerControlsLib " %>

13. To instantiate or use the custom control on the Web Forms page, add the following line of code in the
    tags.

    Note In this code, SimpleServerControl is the control class name inside the class library.
14. Run the Web Forms page, and you will see the output from the custom control.

If you are not using Visual Studio, you need to perform the following steps:

1. Open any text editor.
2. Create a file named SimpleServerControl.cs, and write the code as given in steps 1 through 14.
3. In the PATH variable, add the following path:
   c:\windows (winnt)\Microsoft.Net\Framework\v1.1.4322
4. Start a command prompt, and go to the location where SimpleServerControl.cs is present.
5. Run the following command:
   csc /t:library /out: CustomServerControlsLib. SimpleServerControl.dll /r:System.dll /r:System.Web.dll SimpleServerControl.cs
   For more information about the C# compiler (csc.exe), visit the following MSDN Web site:
   http://msdn2.microsoft.com/en-us/library/1700bbwd(vs.71).aspx (http://msdn2.microsoft.com/en-us/library/1700bbwd(vs.71).aspx)
6. To run the custom control on the Web Forms page, do the following:
   1. Create a directory under the wwwroot folder.
   2. Start Microsoft Internet Information Services (IIS) Manager, and mark the new directory as the virtual root directory.
   3. Create a Bin folder under the new directory.
   4. Copy the custom control DLL into the Bin folder.
   5. Place the sample Web Forms page that you created in the previous steps inside the new directory.
   6. Run the sample page from IIS Manager.

Now that you have built a simple custom control, let's look at how to expose properties and apply design-time attributes on that custom control.

How to expose properties on the custom control

I will build on the previous example and introduce one or more properties that can be configured while using the custom control on the Web Forms page.

The following example shows how to define a property that will display a message from the control a certain number of times, as specified in the property of the control:

1. Open SimpleServerControl.cs in a text editor.
2. Add a property in the SimpleServerControl class.

   public class SimpleServerControl : Control
   {
      private int noOfTimes;
      public int NoOfTimes
      {
          get { return this.noOfTimes; }
          set { this.noOfTimes = value; }
      } 
      protected override void Render (HtmlTextWriter writer)
      {
        for (int i=0; i< NoOfTimes; i++)
        {
          write.Write("Hello World.."+"
   ");
        } 
      }
   }
   

3. Compile the custom control.
4. To use the custom control on the Web Forms page, add the new property to the control declaration.

5. Running the page will display the message "Hello world" from the custom control as many times as specified in the property of the control.

How to apply design-time attributes on the custom control

Why design-time attributes are needed

The custom control that you built in the previous example works as expected. However, if you want to use that control in Visual Studio, you may want the NoOfTimes property to be automatically highlighted in the Properties window whenever the custom control is selected at design time.

To make this happen, you need to provide the metadata information to Visual Studio, which you can do by using a feature in Visual Studio called attributes. Attributes can define a class, a method, a property, or a field. When Visual Studio loads the custom control's class, it checks for any attributes defined at the class, method, property, or field level and changes the behavior of the custom control at design time accordingly.

To find more information about attributes, visit the following MSDN Web site:

http://msdn2.microsoft.com/en-us/library/Aa288059(VS.71).aspx (http://msdn2.microsoft.com/en-us/library/Aa288059(VS.71).aspx)

Let's build a sample that uses commonly used attributes:

1. Open SimpleServerControl.cs in a text editor.
2. Introduce some basic attributes at the class level, for example, DefaultProperty, ToolboxData, and TagPrefixAttrbute. We'll build our sample on these three attributes.

           [
   // Specify the default property for the control.
   DefaultProperty("DefaultProperty"),
   
   // Specify the tag that is written to the aspx page when the
           // control is dragged from the Toolbox to the Design view. 
   // However this tag is optional since the designer automatically 
   // generates the default tag if it is not specified.
   ToolboxData("<{0}:ControlWithAttributes runat=\"server\">" +
   "")
   ]
   public class ControlWithAttributes : Control
   {
   private string _defaultProperty;
   public string DefaultProperty
   {
   get { return "This is a default property value"; }
   set { this._defaultProperty = value; }
   }
   
   protected override void Render(HtmlTextWriter writer)
   {
   writer.Write("Default Property --> " + 
   DefaultProperty + "");
   }
            }
   

3. There is one more tag called TagPrefixAttrbute. It is an assembly-level attribute that provides a prefix to a tag when you drag the control from the Toolbox to the designer. Otherwise, the designer generates a prefix such as "cc1" by default. TagPrefixAttrbute is not directly applied to the control class. To apply TagPrefixAttrbute, open AssemblyInfo.cs, include the following line of code, and then rebuild the project.

   [assembly:TagPrefix("ServerControlsLib ", "MyControl")]

   Note If you want to build the source using the command line, you need to create the AssemblyInfo.cs file, place the file in the directory that contains all the source files, and run the following command to build the control:
   > csc /t:library /out: ServerControlsLib.dll /r:System.dll /r :System.Web.dll *.cs

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What are the basic differences between user controls and custom controls?

Now that you have a basic idea of what user controls and custom controls are and how to create them, let's take a quick look at the differences between the two.

Collapse this tableExpand this table

Factors	User control	Custom control
Deployment	Designed for single-application scenarios Deployed in the source form (.ascx) along with the source code of the application If the same control needs to be used in more than one application, it introduces redundancy and maintenance problems	Designed so that it can be used by more than one application Deployed either in the application's Bin directory or in the global assembly cache Distributed easily and without problems associated with redundancy and maintenance
Creation	Creation is similar to the way Web Forms pages are created; well-suited for rapid application development (RAD)	Writing involves lots of code because there is no designer support
Content	A much better choice when you need static content within a fixed layout, for example, when you make headers and footers	More suited for when an application requires dynamic content to be displayed; can be reused across an application, for example, for a data bound table control with dynamic rows
Design	Writing doesn't require much application designing because they are authored at design time and mostly contain static data	Writing from scratch requires a good understanding of the control's life cycle and the order in which events execute, which is normally taken care of in user controls

Please refer the below link

http://support.microsoft.com/kb/893667



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