Introduction to ASP+ web controls

Introduction

This Q.A. series provides you with reference as well as examples of using ASP+ web controls. At the end of the series you will find a ZIP file for download which contains sample ASP+ pages. This Q.A mainly focuses on non-data bound controls. The examples are that way very basic but that do illustrate common use of the control under consideration. The NGWS SDK documentation is the ultimate source of information on how to use ASP+. This Q.A. just provides most common features but its handy as it contains everything in one page!

To run these samples you will need Windows2000 server with NGWS SDK installed. You will also need IIS 5.0 and IE 5.5.

If you explore ASP+ further on your own and have something interesting to share please contact me at bipinjoshi@yahoo.com

What are web controls ?

Web controls are basically HTML elements wrapped under easy to use scripting tags of ASP+ and provide rich functionality in your FORMs or pages. Web controls range from simple text box to advance girds and lists. Some of the controls like data grid can be bound to data sources much like Visual Basic data bound controls.

What are advantages of web controls ?

• They are highly customizable and provide common properties and methods throughout.
• Even though web controls provide rich functionality finally they are rendered as plain HTML in the client browser thus avoiding browser compatibility problems.
• They can be used in object oriented manner much like Visual Basic controls.
• They are processed at server side. This makes ASP+ page much readable and cleaner as compared to traditional ASP page.
• They can be data bound
• State maintenance is automatically taken care by ASP+

What are common web controls available?

Following is a list of common web controls :

• Label
• Panel
• Button
• TextBox
• CheckBox
• RadioButton
• RadioButtonList
• ListBox
• DropDownList
• Table/TableRow/TableCell
• DataGrid
• DataList
• Repeater
• Calender
• Validation controls

How do I handle Web control events?

Web control are processed at server side. This means that all the events generated by a control will be handled at server end. The event handling has changed with ASP+. Each event handler now has following syntax :

public sub myeventhandler(source as Object, evt as EventArgs)
'access your web controls here and
'manipulate their properties
end sub

Here, source is the object which caused the event to be raised and evt is an object providing more information about the event.

Note : I could not found clearly how to use these parameters from NGWS preview SDK. Also, it is not clear how to pass my own parameters to the event handlers.

What precautions are needed while coding for web controls ?

• All controls must have id attribute set
• All controls must be set to process at server side
• All controls must be enclosed within HTML FORM element
• The form must be set to process server side
• All controls must have proper start and end tags i.e. <control></control> or <control />
• If you want to maintain control state you must use POST method

How do I use Label web control ?

Lable web control is generally used to display labels for other FORM elements. The general syntax is :

<asp:Label id="label1"  Text="my label text" />

How do I use Button web control ?

Button web control is used to represent an action like Ok, Submit, Cancel etc.

Syntax :

<asp:Button id="button1" Text="My button caption" OnClick="myevthandler" />

How do I use Panel web control?

It is a wrapper for HTML <DIV> tag.

Syntax :

<asp:Panel id="Panel1" runat="server"     BackImageUrl="url" HorizontalAlign="Center|Justify|Left|NotSet|Right"
   Wrap="True|False"
/>

Or

<asp:Panel id="Panel1" runat="server" >
  ------ other controls go here -----------
</asp:Panel>

How do I use TextBox web control?

Text box web control is used to accept user input in your web forms.

Syntax :

<asp:TextBox id=value runat="SERVER" Text="text" TextMode="Single | Multiline | Password" />

How do I use CheckBox web control?

Check box is used to indicate on or off state.

Syntax :

<asp:CheckBox id="CheckBox1" runat="server"    Text="label"  OnCheckedChanged="OnCheckedChangedMethod"
/>

How do I use RadioButton web control?

Syntax :

<asp:RadioButton id="RadioButton1" runat="server" Text="label"
   OnCheckedChanged="OnCheckedChangedMethod"
/>

How do I use  ListBox or DropDownList web controls?

ListBox presents a list of item from which user can select one or many items.

<asp:ListBox id="Listbox1" runat="server"
   OnSelectedIndexChanged="OnSelectedIndexChangedMethod"
/>
   <asp:Listitem value="value" selected="True|False">
         Text
   </asp:Listitem>
</SP:ListBox>

Or

<asp:DropDownList  id="Combo1" runat="server"    OnSelectedIndexChanged="OnSelectedIndexChangedMethod"
/>
   <asp:Listitem value="value" selected="True|False">
         Text
   </asp:Listitem>
</asp:DropDownList>

How do I use Table web controls?

Table web controls represent HTML table. You can manipulate rows and columns programmatically.

<asp:Table id="Table1" runat="server" />
   <asp:TableRow>
      <asp:TableCell>
         Cell text
      </asp:TableCell>
   </asp:TableRow>
</asp:Table>