Niranjan Kala's blog: Difference Between User Controls and Custom Control

User control
1) Reusability web page
2) We can't add to toolbox
3) Just drag and drop from solution explorer to page (aspx)
4) U can register user control to. Aspx page by Register tag
5) A separate copy of the control is required in each application
6) Good for static layout
7) Easier to create
8)Not complied into DLL
9) Here page (user page) can be converted as control then
We can use as control in aspx

Custom controls
1) Reusability of control (or extend functionalities of existing control)
2) We can add toolbox
3) Just drag and drop from toolbox
4) U can register user control to. Aspx page by Register tag
5) A single copy of the control is required in each application
6) Good for dynamics layout
7) Hard to create
8) Compiled in to dll

User Controls

User controls are custom, reusable controls, and they use the same techniques that are employed by HTML
and Web server controls. They offer an easy way to partition and reuse common user interfaces across
ASP.NET Web applications. They use the same Web Forms programming model on which a Web Forms
page works. For more details about the Web Forms programming model.

How to create a user control

The syntax you use to create a user control is similar to the syntax you use to create a Web Forms page (.aspx).

The only difference is that a user control does not include the <html>, <body>, and <form> elements since a

Web Forms page hosts the user control. To create a user control, follow these steps:

Open a text or HTML editor, and create a server-side code block exposing all the properties, methods,
and events.

<script language="C#" runat="server">    public void button1_Click(object sender, EventArgs e)

label1.Text = "Hello World!!!";

 </script>

Create a user interface for the user control.

<asp:Label id="label1" runat="server"/>

  <br><br>

<asp:button id="button1" text="Hit" OnClick="button1_Click" 
runat="server" />

How to use a user control in a Web Forms page

Create a new Web Forms page (.aspx) in Microsoft Visual Studio .NET 2002, Microsoft Visual Studio
.NET 2003, Microsoft Visual Studio 2005, or any text editor.

Declare the @ Register directive. For example, use the following code.

<%@ Register TagPrefix="UC" TagName="TestControl" 
                                            Src="test.ascx" %>

Note Assume that the user control and the Web Forms page are in the same location.

To use the user control in the Web Forms page, use the following code after the @ Register directive.

<html>

<body>

<form runat="server">

<UC:TestControl id="Test1" runat="server"/>

</form>

</body>

</html>

How to create an instance of a user control programmatically in the code behind file of a Web Forms page

The previous example instantiated a user control declaratively in a Web Forms page using the @ Register directive. However, you can instantiate a user control dynamically and add it to the page. Here are the steps for doing that:

Create a new Web Forms page in Visual Studio.
Navigate to the code behind file generated for this Web Forms page.

In the Page_Load event of the Page class, write the following code.

// Load the control by calling LoadControl on the page class. Control c1 = LoadControl("test.ascx");              // Add the loaded control in the page controls collection.  Page.Controls.Add(c1);

Note You can add a user control dynamically at certain events of the page life cycle.

How a user control is processed

When a page with a user control is requested, the following occurs:

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.

Custom Controls

Custom controls are compiled code components that execute on the server, expose the object model, and render markup text, such as HTML or XML, as a normal Web Form or user control does.

How to choose the base class for your custom control

To write a custom control, you should directly or indirectly derive the new class from the System.Web.UI.Control class or from the System.Web.UI.WebControls.WebControl class:

You should derive from System.Web.UI.Control if you want the control to render nonvisual
elements. For example, <meta> and <head> 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.

If you want to change the functionality of existing controls, such as a button or label, you can directly derive the new class with these existing classes and can change their default behavior. In brief, the Control class provides the basic functionality by which you can place it in the control tree for a Page class. The WebControl class adds the functionality to the base Control class for displaying visual content on the client computer. For example, you can use the WebControl class to control the look and styles through properties like font, color, and height.

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

Start Visual Studio.
Create a class library project, and give it a name, for example, CustomServerControlsLib.
Add a source file to the project, for example, SimpleServerControl.cs.
Include the reference of the System.Web namespace in the references section.

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

Inherit the SimpleServerControls class with the Control base class.
```
public class SimpleServerControl : Control
```
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.
Compile the class library project. It will generate the DLL output.
Open an existing or create a new ASP.NET Web application project.
Add a Web Forms page where the custom control can be used.
Add a reference to the class library in the references section of the ASP.NET project.

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

To instantiate or use the custom control on the Web Forms page, add the following line of code in the
<form> tags.
```
<form id="Form1" method="post" runat="server">     <CC:SimpleServerControl id="ctlSimpleControl" 
runat="server">     </CC:SimpleServerControl > </form> 
```
Note In this code, SimpleServerControl is the control class name inside the class library.
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:

Open any text editor.
Create a file named SimpleServerControl.cs, and write the code as given in steps 1 through 14.
In the PATH variable, add the following path:
c:\windows (winnt)\Microsoft.Net\Framework\v1.1.4322
Start a command prompt, and go to the location where SimpleServerControl.cs is present.
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),
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:

Open SimpleServerControl.cs in a text editor.

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.."+"<BR>");      }     } }

Compile the custom control.

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

<CC:SimpleServerControl id="ctlSimpleControl" NoOfTimes="5" 
runat="server"></CC:SimpleServerControl>

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

Open SimpleServerControl.cs in a text editor.

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\">" +   "</{0}:ControlWithAttributes>")  ] 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 --> <B>" +    DefaultProperty + "</B>");  }  }

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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Tuesday, February 15, 2011

Difference Between User Controls and Custom Control