System Test in Interview on ListBox

This blog explains -

How to use classes and inheritance.
CRUD operations with listbox using databse.
How to use split function.
How to validate the textboxes using javascript.

It also covers the the following System Test question,

Create a class for the math ( "+","-") operations -- name the class "MathOp".
Extend the class using inheritance to include ("*","/") name the class "MathOp2".
Create the following class/function when select a line from the list box, the user should be able to modify the values/operations and save it to the listbox/database Let’s say the user clicked on “1+3=4” , the values 1,3 should be displayed in the input text boxes.

Step 1: At DataBase.

I use the following table to demonstrate the above concepts.

Create table MathRresults(
ID int primary key identity(1,1),
Result varchar(20)
)

Application

Step 2: Creating the project.

Now create the project using the following.

Go to Start, then All Programs and click Microsoft Visual Studio 2010.

Go to File, then click New, Project..., Visual C# , Web. Then select ASP.NET Empty Web Application.

Provide the project a name and specify the location.

Step 3 : Web.Config.

Create the connection string in the Web.Config file as in the following code snippet:

<connectionStrings>
<add name="conStr"
connectionString="Password= 1234; User ID=sa; Database=DB_Jai; Data Source=."
providerName="System.Data.SqlClient"/>
</connectionStrings>

Next: Right-click on Solution Explorer and add a web form to your project.

Make your .aspx as follows -

calculation

Step 4 : JavaScript Validations.

Use the following code to validate the textboxes.

< script type = "text/javascript" > function Valid()
{
if (document.getElementById('<%=txtFirstNumber.ClientID%>').value.trim() == "") {
var msg = document.getElementById('<%=lblMsg.ClientID %>');
msg.innerHTML = "Please enter First Number";
msg.style.color = "red";
document.getElementById('<%=txtFirstNumber.ClientID%>').focus();
return false;
}
if (document.getElementById('<%=txtSecondNumber.ClientID%>').value.trim() == "") {
var msg = document.getElementById('<%=lblMsg.ClientID %>');
msg.innerHTML = "Please enter Second Number";
msg.style.color = "red";
document.getElementById('<%=txtSecondNumber.ClientID%>').focus();
return false;
}
}
< /script>

CodeBehind

Add the following namespaces:

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

Invoke the ConnectionString from Web.Config as in the following:

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConStr"].ConnectionString);

Step 5 : Declare global variables.

private Decimal Num1;
private Decimal Num2;
string constr = ConfigurationManager.ConnectionStrings["connectionStr"].ConnectionString;

Step 6: Classes and Inheritance.

MathOp class Contains two methods that are Add, Subtract.

MathOp2 class Contains two methods that are Mul, Div.

public class MathOp
{
public Decimal Add(Decimal value1, Decimal value2)
{
return (value1 + value2);
}
public Decimal Subtract(Decimal value1, Decimal value2)
{
return (value1 - value2);
}
}
public class MathOp2: MathOp
{
public Decimal Mul(Decimal value1, Decimal value2)
{
return (value1 * value2);
}
public Decimal Div(Decimal value1, Decimal value2)
{
return (value1 / value2);
}
}

Step 7: User defined methods.

//Clear () method is used to clear the textbox box values.
private void Clear()
{
txtFirstNumber.Text = string.Empty;
txtSecondNumber.Text = string.Empty;
lblResult.Text = string.Empty;
lblMsg.Text = string.Empty;
}
//saveResult() method is used to save the result sets in database.
private void saveResult()
{
SqlConnection con = new SqlConnection(constr);
SqlCommand cmd = new SqlCommand("insert into MathRresults values('" + lblResult.Text + "')", con);
SqlDataReader dbr;
try
{
con.Open();
dbr = cmd.ExecuteReader();
lblMsg.Text = "Values saved Successfully";
lblMsg.ForeColor = Color.Green;
dbr.Read();
}
catch (Exception ex)
{
lblMsg.Text = "Failed to Save because :" + ex;
lblMsg.ForeColor = Color.Red;
}
con.Close();
BindResultsToListview();
}
// UpdateResult() method is used to update the result sets with existing records in database.
private void UpdateResult()
{
int ? id = null;
foreach(ListItem li in ListBox1.Items)
{
if (li.Selected == true)
{
id = Convert.ToInt32(ListBox1.SelectedValue);
}
}
SqlConnection con = new SqlConnection(constr);
SqlCommand cmd = new SqlCommand("Update MathRresults set Result = '" + lblResult.Text + "' Where ID = '" + id + "'", con);
SqlDataReader dbr;
try
{
con.Open();
dbr = cmd.ExecuteReader();
lblMsg.Text = "Values Updated Successfully";
lblMsg.ForeColor = Color.Green;
dbr.Read();
//while (dbr.Read())
//{
//}
}
catch (Exception ex)
{
lblMsg.Text = "Failed to update because:" + ex;
lblMsg.ForeColor = Color.Red;
}
finally
{
con.Close();
BindResultsToListview();
}
}
//BindResultsToListview Method is used to bind the operations to ListBox.
private void BindResultsToListview()
{
Clear();
SqlConnection con = new SqlConnection(constr);
string cmd = "Select Id, Result from MathRresults";
SqlDataAdapter adpt = new SqlDataAdapter(cmd, con);
DataSet ds = new DataSet();
adpt.Fill(ds, "MathRresults");
DataTable myDataTable = ds.Tables[0];
if (ds.Tables.Count > 0 && ds != null && ds.Tables[0].Rows.Count > 0) {
ListBox1.DataSource = ds;
ListBox1.DataValueField = "ID";
ListBox1.DataTextField = "Result";
ListBox1.DataBind();
}
}
//DeleteFromListView is used to delete the selected item in ListBox.
private int DeleteFromListView(int id)
{
//Here using statement is automatically close the connections
using(SqlConnection con = new SqlConnection(constr))
{
SqlCommand cmd = new SqlCommand("delete from MathRresults where id = " + id + "", con);
con.Open();
cmd.ExecuteNonQuery();
return 0;
}
}

Step 8 : Page load.

Copy the following code in page_ load.

if (!Page.IsPostBack)
{
BindResultsToListview();
}
Clear();
//txtFirstNumber value to be assigned to Num1 variable.
Num1 = Convert.ToDecimal(txtFirstNumber.Text);
//txtSecondNumber value to be assigned to Num2 variable.
Num2 = Convert.ToDecimal(txtSecondNumber.Text);

Step 9: Addition.

To add or update two values and save the result set in database –

protected void btnAdd_Click(object sender, EventArgs e)
{
MathOp2 m = new MathOp2();
Decimal additon = m.Add(Num1, Num2);
lblResult.Text = (Num1 + ("+" + (Num2 + ("=" + additon))));
lblResult.ForeColor = Color.Green;
//this is pretty simple
//if your not selected any item in listbox it's save your result as a new record in database.
//if your selected any item in listbox it's update your result with existing record in database.
if (ListBox1.SelectedValue == string.Empty)
{
saveResult();
}
else
{
UpdateResult();
}
}

Step 10: Subtraction.

To Subract values and save the result set in database –

protected void btnSubtract_Click(object sender, EventArgs e)
{
MathOp2 m = new MathOp2();
Decimal subtraction = m.Subtract(Num1, Num2);
lblResult.Text = (Num1 + ("-" + (Num2 + ("=" + subtraction))));
lblResult.ForeColor = Color.Green;
if (ListBox1.SelectedValue == string.Empty) saveResult();
else UpdateResult();
}

Step 11: Multiplication.

To multipliy two values and save the result set in database -

protected void btnMultiply_Click(object sender, EventArgs e)
{
MathOp2 m = new MathOp2();
Decimal division = m.Mul(Num1, Num2);
lblResult.Text = (Num1 + ("*" + (Num2 + ("=" + division))));
lblResult.ForeColor = Color.Green;
if (ListBox1.SelectedValue == string.Empty) saveResult();
else UpdateResult();
}

Step 12 : Division.

For division of two values and save the result set in database -

protected void btnDivide_Click(object sender, EventArgs e)
{
// if txtSecondNumber value is zero, then the result would be infinite.
// To prevent that make one alert for user that "Divide By Zero is Invalid"
if (Num2 == 0)
{
lblMsg.Text = "Divide By Zero is Invalid";
lblMsg.ForeColor = Color.Red;
return;
}
MathOp2 m = new MathOp2();
Decimal division = m.Div(Num1, Num2);
lblResult.Text = (Num1 + ("/" + (Num2 + ("=" + division))));
lblResult.ForeColor = Color.Green;
if (ListBox1.SelectedValue == string.Empty) saveResult();
else UpdateResult();
}

Step 13 : Delete the selected listbox value.

To delete the selected item from listbox as well as database –

protected void btnDelete_Click(object sender, EventArgs e)
{
lblResult.Text = string.Empty;
lblMsg.Text = string.Empty;
for (int i = 0; i <= ListBox1.Items.Count - 1; i++)
{
if (ListBox1.Items[i].Selected != false)
{
DeleteFromListView(Convert.ToInt32(ListBox1.Items[i].Value));
}
}
ListBox1.Items.Clear();
BindResultsToListview();
lblMsg.Text = "Selected Value deleted successfully";
}
// ListBox1_SelectedIndexChanged
protected void ListBox1_SelectedIndexChanged(object sender, EventArgs e)
{
lblMsg.Text = string.Empty;
if (ListBox1.SelectedValue == string.Empty)
{
return;
}
int ? id = null;
string selectedtext = null;
foreach(ListItem li in ListBox1.Items)
{
if (li.Selected == true)
{
id = Convert.ToInt32(ListBox1.SelectedValue);
}
}
SqlConnection con = new SqlConnection(constr);
SqlDataAdapter adpt = new SqlDataAdapter("Select * from MathRresults Where Id = '" + id + "'", con);
DataSet ds = new DataSet();
adpt.Fill(ds, "MathRresults");
DataTable myDataTable = ds.Tables[0];
if (ds.Tables.Count > 0 && ds != null && ds.Tables[0].Rows.Count > 0)
{
selectedtext = ds.Tables[0].Rows[0]["Result"].ToString();
}
//Split the item by the operator and the '=' into an array of strings
string[] parts = selectedtext.Split('+', '-', '*', '/', '=');
if (parts.Length > 2) {
//Define a variable for each part
string part1 = parts[0].Trim();
string part2 = parts[1].Trim();
string part3 = parts[2].Trim();
txtFirstNumber.Text = part1;
txtSecondNumber.Text = part2;
lblResult.Text = part3;
}
}

I hope you enjoyed it.