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http://in.geocities.com/rsramsam/aspdotnet1.htm

ASP.Net using C#....

(A Quick tour) -R.S.RAMASWAMY

(rsramsam@yahoo.co.in)

( published in Feb-2004 issue of

DEVELOPERIQ magazine.

www.developeriq.com)

--------------------

It can be claimed without being far off the mark, that ASP.net is the prize-offering in the DotNet platform. ASP.Net programs can bewritten in either C# or in VB.Net. However, it is better to use C#. Professional programming mostly requires C/C++/Java and C# is very much similar to these languages.Thus, it will be easier to switch over to other languages if necessary. If we want to write our program, using J# also, it will entail minimum change in style of coding..Moreover, C# is the language being actively promoted by Microsoft for certain advanced level work.

If we want to work in ASP.net , but in Linux platform using MONO, then C# is a ' must' at present, though in future, it may be possible to create ASP.net programs in other languages in MONO.So, it will be better to switch over to C# from VB world.

VB.net however is only very slightly different from C# code.VB.net may seem to be the easier choice as it is the default language for 'ASP.net in Microsoft platform' and is not case-sensitive( how swiftly, things are changing! Who would have predicted that we may have to qualify ASP.net with reference to the platform?) . But, being case-indifferent is not the best way to thrive in professional software field!.

Another point,which should be stressed is that though there are classes in' Windows.Forms' and 'Web.Forms', bearing the same name,their behaviour is different. ( For example, Datagrid).However, a lot of C# code will work equally well in desktop as well as in ASP.net!

ASP.net makes VB programmers , equally productive in Web-Applications as well as desktop apps.Similarly, ASP.net ,gives the great ease of webforms and webservice to j2ee hands and removes all hurdles. For all appearances, ASP.net programming is just like VB programming except that instead of getting the gui elements by drag and drop, we have to write some rudimentary html-like code. True, even this difference vanishes if we are using VisualStudio.net but we will be using DotNet Framework SDK only, for our lessons because it is LEGALLY free for professional development and our method will be useful even in Linux world. And , as we are studying ASP.net in C#,

we must write the code with case-awareness.

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The major topics in ASP.net are listed below.

1) ASP.net Web-Form controls

2) Database operations, Data-bound controls

3) Graphics & Dynamic graphics creation

4) XML operations

5) ASP.net Validation & special controls

6) Separation of logic & presentation

7) XML-WebService

8) Mobile Applications.

9) Session Management

10) File-Upload , email etc.

------------------------

These are the topics that are essential to get started with ASP.net. If we know these ,we would have covered about 75% and we can always learn the remaining topics , after this.

If we have some prior knowledge of Java,VB and ASP, and if we actually learn by doing,we can learn ASP.net very easily.It is that very programmer-friendly environment, but so much more fun,powerful and modern!

---------------------------------------------

However, some readers may find it very difficult to instal DotNet SDK and IIS-5 properly and run their first asp.net program successfully. This may well be the most difficult part.For Windows programmers,first, we should remember that Asp.net runs only in Windows-2000. Secondly, it requires InternetInformationServer-5. This is not automatically installed.But it is available separately in Windows-2000 CD. We also need InternetExplorer 5.5 or above(6.0 preferable). Microsoft Data Access Components 2.7 (MDAC2.7)

also has to be installed. We must checkup whether the server is working by creating a simple page as:

'D:\inetpub\wwwroot\welcome.htm'.

---------------------

<html> <body>welcome</body></html>

-------------------

& viewing it in browser. as 'http://localhost/welcome.htm'.

After this, we must checkup a simple 'demo1.aspx' as given below. If we get correct result, we are on our way.

--------------------------------------------

(TOPIC-1)....... ASP.net WebForm Controls

===========================

Let us straight away begin with a simple ASP.net example using WebForm controls.

We create demo1.aspx file in 'lessons'folder

,as (d:\inetpub\wwwroot\lessons\demo1.aspx)

-----------------------------------------------

<%@ language="C#" debug="true" %>

void job1(Object o, EventArgs e)

{

String s = text1.Text;

text2.Text=s;

}

</script>

<asp:textbox id=text1 runat=server />

<asp:button text="click"

onclick=job1 runat=server />

<asp:textbox id=text2 runat=server />

</form></body></html>

-----------------------------------------------

In C#,all Class names,functions and properties begin with Capital letter. Instead of camel-

back notation as in Java, we use capitalletter

for that purpose also.(see how EventArgs is

typed in the script section).These rules are

the same as in MFC and so only Java

programmers , accustomed as they are to

function names beginning with 'lower case' and camelback notation will have some initial difficulty.

-----------------------------------------------

In reading ASP.net code, we always begin with

the html section. It looks like the usual html

form, except that asp:textbox and asp:button

have been used. Secondly, each of these lines

ends with 'runat=server' attribute.The html

section is NOT case-sensitive.(but the script section is definitely case-sensitive...in C#).Carefully note that we have not

specifically mentioned GET or POST.

The default is POST. (Posting to itself!)

When we start the browser and type the URL as:

'http://localhost/lessons/demo1.aspx',

and hit 'enter', we get a textbox(text1),a

button and another textbox(text2).Let us type something in text1 and click the button.

What we typed in text1 now appears in text2!

( Due to compilation time, allow for some

delay).

(Is this ASP.net or VB or JAVA?).That easy!

Actually, what is being done behind the

scene is very much complex! The 'apparently

html' code is compiled in the server and the resultant html is sent to the browser. If we

try to see the source in the browser, we see standard html for textboxes and button.We also

see some strange characters dubbed as 'viewstate'!.and 'hidden' . When any button is clicked in ASP.net, it is equivalent to

submitting the form to the server! The code

re-creates the form's controls and fills up

the data as required.

The data typed in text1 is retained as if we

are in VB!Anyone with familiarity in ASP will

realise,that to create the same effect in

plain ASP requires imagination and dynamic

form creation.

-----------------------

Now that we have seen a simple example,let us

see the syntax for creating a few other gui elements. ----------------------------------------------

<asp:dropdownlist id=combo1 runat=server />

<asp:listbox id=list1 runat=server />

<asp:listbox id=list2

selectionmode=multiple runat=server />

<asp:checkboxlist

id=checklist1 runat=server />

<asp:radiobuttonlist

id=radiolist1 runat=server />

-----------------------------------------------

We can populate these controls by the uniform method of first creating a vector, adding elements to that vector and binding the respective control to the vector.

(Actually, the class-name is ArrayList but we

name the variable as vector so that Java coders will find it easy to follow.)

For example,

ArrayList vector1;

vector1 = new ArrayList();

vector1.Add("Madras");

vector1.Add("Bombay");

vector1.Add("Delhi");

combo1.DataSource=vector1;

combo1.DataBind();

--------------------------------------

Considering another example,

ArrayList vector2;

vector2=new ArrayList();

vector2.Add("COBOL");

vector2.Add("C++");

vector2.Add("Java");

vector2.Add("MFC");

vector2.Add("C#");

checklist1.DataSource=vector2;

checklist1.DataBind();

------------------------------------------

Exactly, same method as the above,is followed

for populating simple-list & multi-list and radiobutton-list.As this is done in scripting section, the html part is absolutely free from clutter!

-----------------------------------------------

How do we extract data from these controls?

Simple! In combo,simple-list and radiolist, we have to get just one string. So,

--------------------------------------------

String s1=combo1.SelectedItem.Text;

String s2=list1.SelectedItem.Text;

String s3=radio1.SelectedItem.Text;

--------------------------------------------

In multi-list and checklist, we have to extract more than one item. So, the syntax

is special.

------------------------------------

For multi-list,

String s = "";

foreach(ListItem item in list2.Items)

{

if(item.Selected)

{

String a=item.Text;

list3.Items.Add(s);

}

-----------------------------------------------

'ListItem' is a class name.

'Items' is a property of listbox.

'Selected' is a property.

'Text' also is a property.

'Add' is a method.

--------------------------------------------

For check-list,

String s = "";

foreach(ListItem item in checklist1.Items)

{

if(item.Selected)

{

String a=item.Text;

List3.Items.Add(s);

}

So, where is the difference? It occurs in the source of 'Items'.

-----------------------------------------------

How do we create the equivalent of TextArea?

As is VB, it is just a textbox with multiline property.

<asp:textbox id=area1 textmode=multiline

rows=6 columns=20 runat=server />

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Let us now consider a second example

(demo2.aspx). The purpose is to illustrate

creation of combo,multi-list and simple-list controls and the ususl operations in them.

In this demo,a combo offers options for

various Engg branches. When we choose the

required branch, a list of best students of

that branch is displayed in multi-list (list1)

We can select a few in a single step and

add them to simple-list(list2). If we want to delete any name from list2, we can.

We can repeat the process for each branch and

arrive at the final selection list.In essence, this is nothing but the famous 'Shopping Cart' problem of the web.The only difference is that

we have not populated the controls from a

database . But once we understand this simple example, a real world example is not all that difficult and is being given after covering

database.

We want the combo to be populated when the

form first appears but not afterwards.

(similar to form_load in vb).But, each time

a button is clicked in ASP.net, the form is

posted back to the server!So, we must ensure

that the combo is not loaded repeatedly.

This is checked up by the conditional :

if(!IsPostBack)

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// d:\inetpub\wwwroot\lessons\demo2.aspx

============================================

<%@ language="C#" debug="True" %>

void Page_Load()

{

if( !IsPostBack)

{

ArrayList vector1;

vector1 = new ArrayList();

vector1.Add("Electrical");

vector1.Add("Mechanical");

combo1.DataSource = vector1;

combo1.DataBind();

}

//---------------------------------------

void job1(Object o, EventArgs e)

{

String s = combo1.SelectedItem.Text;

ArrayList vector1;

if(s =="Electrical")

{

vector1=new ArrayList();

vector1.Add("Thomas");

vector1.Add("Robert");

vector1.Add("Sam");

}

if(s == "Mechanical")

{

vector1=new ArrayList();

vector1.Add("James");

vector1.Add("Jones");

vector1.Add("Tom");

}

list1.DataSource = vector1;

list1.DataBind();

}

//--------------------------------------

void job2(Object o, EventArgs e)

{

foreach (ListItem item in list1.Items)

{

if (item.Selected)

{

String a = item.text;

list2.Items.Add(a);

}

//--------------------------------------

void job3(Object o, EventArgs e)

{

list2.Items.Remove(list2.SelectedItem);

}

//----------------------------------------

</script>

<asp:dropdownlist id="combo1" runat=server />

<asp:listbox id=list1

selectionmode=multiple runat=server />

<asp:listbox id=list2 runat=server />

<asp:button text="select branch"

onclick=job1 runat=server />

<asp:button text="add"

onclick=job2 runat=server />

<asp:button text="remove"

onclick=job3 runat=server />

</form>

</body>

</html>

===============================================

Though, we have not covered all the controls,

these are enough for the present.We now move on to Database opearations.

==============================================

(SECTION-2) DATABASE OPERATIONS

------------------------------

ADO.net offers two sets of packages for Database operations.

a) OleDb

b) SqlClient

----

As we know,Microsoft offers an indstrial grade

DB product known as SQLSERVER. In DOTNET, Microsoft have provided a special low-level

driver, especially for accessing SQLSERVER. This speeds up the operations. For other

databases like Oracle ,Access etc,they provide another set known as OleDb.

-----------------------------------------------

Dot.net offers two methods of Database operations.

SqlClient

=========

a) SqlDataReader

b) SqlDataAdapter & DataSet

-----

OleDb

-----------

a) OleDbReader

b) OleDbDataAdapter & dataset -----------------------------------------------

The Reader type is cursor based and fast&

does not bring the entire table into the

memory.

DataAdapater and DataSet method brings the

entire database into memory. This is known

as 'In-memory database'. After this, the

connection to the database is cutoff. This

enables other clients to access the database. After, viewing/manipulating the records, the

data can be stored back in database , if

needed. This is the advantage of Dataset

approach. But, if the table is very large, it

may slow down because of too much memory consumption.(For those familiar with XML

parsing, these are similar to the merits of

SAX & DOM spectively).

However, for XML opeartions , DataSet is

very easy and powerful. So, for the usual operations like 'select','insert into' , 'delete' and 'update' , we can use the

Reader method.For XML opeartions,we can use DataSet method.. ***********************************************

The following code-examples give illustration.

1) Sample code: SqlSever: Reader approach

-----------------------------------------

<%@ page language="c#" %>

<%@ Import NameSpace="System.Data.SqlClient"%>

String s1= "Server=localhost;uid=RSR;pwd=sa;database=db";

SqlConnection con= new SqlConnection(s1);

con.Open();

String sql="select * from table1";

SqlCommand command=

new SqlCommand( sql, con);

SqlDataReader reader=

command.ExecuteReader();

while(reader.Read())

{

Response.Write(reader[0].ToString());

Response.Write("<br>");

}

reader.Close();

con.Close();

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2) Sample Code: SqlServer DataSet approach

---------------------------------------------

<%@ page language="c#" %>

<%@ Import NameSpace="System.Data.SqlClient"%>