.Net Nullable Types

A variable of a nullable type can be used to store the normal range of values allowed by the underlying data type plus the Null. Nullable types are instances of System.Nullable.

Since reference types already supports Null, nullable types represent value type variables which supports null.

For example Nullable<bool> (or spoken like nullable of bool) can be used to store true, false and null.

There are two ways to declare a nullable variable.

Method 1

int? i; // Declaring
i = null; // Initializing

int? i = 4; // Declariong and initializing

Method 2

Nullable<int> a; // Declaring
a = 4; // Initializing

Nullable<int> a = null; // Declariong and initializing

As you see above assigning values to a nullable is same as for a normal variable. But when retrieving the value you need to be little careful.

Method 1 – Using GetValueOrDefault

GetValueOrDefault property is available for nullable variables. If the variable is null it will get the default value for the type otherwise the actual value it contains.

textBox1.Text += "Value of i - " + i.GetValueOrDefault();

Method 2 – Using variable.Value

When you are going to retrieve the value inside the variable using .Value be careful to first check whether there is actually a value in the variable, otherwise .Net will generate an InvalidOperationException with a description of “Nullable object must have a value”.

// \r\n is used to insert a new line.
if (i == null)
    textBox1.Text += "\r\n" + "i is Null";
else
    textBox1.Text += "\r\n" + "i is - " + i.Value;

or

// Environment.NewLine is equal to placing a new line or \r\n.
if (a.HasValue)
    textBox1.Text += Environment.NewLine + "a has - " + a.Value;
else
    textBox1.Text += Environment.NewLine + "a has Null";

The full code would look like the following.

1. // Declaring Method 1
2. int? i; // Declaring
3. i = null; // Initializing
4. //int? i = 4; // Declariong and initializing
6. // Get value using GetValueOrDefault().
7. textBox1.Text += "Value of i - " + i.GetValueOrDefault();
9. // \r\n is used to insert a new line.
10. if (i == null)
11.     textBox1.Text += "\r\n" + "i is Null";
12. else
13.     textBox1.Text += "\r\n" + "i is - " + i.Value;
15. // Declaring Method 2
16. //Nullable<int> a; // Declaring
17. //a = 4; // Initializing
18. Nullable<int> a = 4; // Declariong and initializing
20. // Environment.NewLine is equal to placing a new line or \r\n.
21. if (a.HasValue)
22.     textBox1.Text += Environment.NewLine + "a has - " + a.Value;
23. else
24.     textBox1.Text += Environment.NewLine + "a has Null";

The output would be,

Value of i - 0
i is Null
a has – 4

You could use the ?? operator to assign the default value for a non nullable variable while the nullable contains null as the current value.

int? Null_X = null;
int NonNull_y = Null_X ?? -1;

Features of Search Engines

How many of you know that common and popular search engines like Google and Bing are providing many other functionalities than searching?

Yes it is true there are many functionalities within them that most of us don’t know.

Following are some features, you can try these out by typing the italic text in your favorite search engine.

1. Finding the date and the time of a place. – “Time Sri Lanka”, “time Melbourne”
2. Checking spelling of words. – “Cheking”, ”mathmatics”
3. Finding results of arithmetic. – “(25*34)+78”, “2**5”
4. Finding the weather if a place. – “Weather Colombo”, “weather Changi”
5. Finding the populations of countries or popular cities. – “Population UK”, “population Sri Lanka”
6. Converting units. – “12.5km in Meters”, “3km in inches”
7. Stock details. – “MSFT”, “AAPL”
8. Find similar word (Synonyms). – “~Cooking”, “~hot drinks”
9. Finding currency values. – “1 GBP in AUD”, “89.34 AUD in USD”
10. Finding maps. – “New York Map”, “Sydney map”
11. Finding definitions of words. – “Define Computer”, “define language”
12. Other than above you can find about Books, Movies, Air Line Schedules etc. But they are widely for other countries like UK, US.

While searching you can use special characters like wild cards, concatenate, subtract to help while searching. Try them out to find the results by your own.

Business Data Catalog - BDC

As of Microsoft, Business Data Catalog is a new feature introduced with SharePoint 2007 which can be used to integrate business data from backend server {Line Of Business (LOB)} applications.

There are few good articles I found in the following web sites if you are interested to read more.

• http://msdn.microsoft.com/en-us/library/ms563661.aspx
• BDC Purpose and Technical Architecture
• Application Definition File (ADF) and its Development
• Developing an ADF to Connect to Web Services
• Consuming Business Data through Web Parts and SharePoint Lists
• Implementing Enterprise Search with Business Data
• Integrating User Profiles with Business Data
• Working with the BDC Object Model
• Using Actions in BDC
• http://blah.winsmarts.com/2007-4-SharePoint_2007__BDC_-_The_Business_Data_Catalog.aspx

How to Read and Write Text

Reading and writing to text files had been made easy by .Net.

Following code will create a text file and insert 2 lines to it and will then read it and display.

1. // System.IO is required for file handling.
2. using System.IO;

1. // Creating a stream writer object.
2. // @ is used before the string to avoid the string getting broken by the /.
3. StreamWriter stWriter = new StreamWriter(@"C:\Backup\File.txt");
5. // Writing into the file.
6. stWriter.Write("It is now ");
7. stWriter.WriteLine(DateTime.Now);
8. stWriter.WriteLine("The End");
10. // Closing the file.
11. stWriter.Close();
13. // Reading the file.
14. // Checking the availability of the file.
15. if (File.Exists(@"C:\Backup\File.txt"))
16. {
17.     // Without using the @, \\ also can be used to represent \ inside of a string.
18.     using (StreamReader stReader = File.OpenText("C:\\Backup\\File.txt"))
19.     {
20.         // Temporary variable.
21.         string str = "";
22.         while ((str = stReader.ReadLine()) != null)
23.         {
24.             // Assigning to a label.
25.             label1.Text += str + "\n";
26.         }
27.     }
28. }
29. else
30.     MessageBox.Show("Error, File cannot be found.");

SharePoint Page Types

Do you know in SharePoint there are two types of pages?

In a SharePoint site each page you see is either a ghosted page or an unghosted page.

Ghosted (Uncustomized) Pages

These are the pages stored in the severs file system but not in the database. The other important thing is these files are common to all the site collections within the SharePoint server and are generally based on the "out of the box" site definition templates. Basically they are working as template files. Ghosted pages are faster since ASP.NET parser will be used to parse them and as you might know ASP.NET parser will compile the page into an assembly on the first time it is rendered, on subsequent executions the compilation is skipped since the assembly is already there.

When ghosted pages are modified by SharePoint designer then they will become unghosted pages, and then SharePoint will start using that file in the future not the file stored in the file system. A common example for this would be the “default.master” file on the “C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\Global“.

Unghosted (Customized) Pages

These are the pages which are stored on the database. Unghosted pages are specific to the SharePoint web site the page is in. If you change these files it will not affect any other site in the same SharePoint server. Unghosted pages will be parsed by the safemode parser which will not compile the pages. The only dynamic code allowed is server-side controls that are marked safe (Safe Controls, Trusted Controls).

Why Ghosting?

This allows SharePoint to,

• Increase it’s performance by enabling caching the main site template into memory and then apply the changes that are stored in the database for the specific file.
• Increases security by not allowing unghosted pages to run code so an attacker who injects code will not be able to crash your server.

Finding the IP Address of the Email Sender

Recently I was bit curios to find out whether we can find the IP address of the sender in an email. After doing some web searching I found interesting sites which describes what needs to be done.

If you like to find out the way to do this please visit and see.

http://www.johnru.com/active-whois/trace-email.html

http://aruljohn.com/info/howtofindipaddress/

Protect HTML Files

Recently I came up with a requirement to protect a website which was created using HTML.

When searching over the internet a team member of mine found a nice software called HTML Guard.

This software is encoding the source of the site so the users will not be able to see the code behind the site. Using this tool you can even block a site to a particular domain. Even the site is downloaded it will not properly run.

The best thing is this has a free version so we can use the full set of features without paying (A small message will come on the top right corner saying the site is encoded by using the tool).

This software is by WulfSoft, thanks guys you have done a good job.

Try out yourself and see.

http://www.htmlguard.com/

Reading and Writing to Excel Files

Even though I posted similar 2 articles in 2008, the code of that article was having few errors. So thought to put more complete post on this.

The code will read an Excel file using an OleDbConnection and will write the same data back to another Excel file. This will explain how to read and write to Excel files. One thing to remember when running this code is to make sure the source Excel file is open. Otherwise you will get an error similar to “External table is not in the expected format.”

Also note that there are few connection string parameters you can use while opening Excel files.

HDR = Yes – Use when first row contains column headers.

HDR = No  - Use when first row contains data.

Excel xx.x – Use the following Table as a guide.

Parameter Value	Excel Version
Excel 12.0	Excel 2007 (Released in 2007)
Excel 11.0	Excel 2003 (Released in 2003)
Excel 10.0	Excel XP (Released in 2001)
Excel 9.0	Excel 2000 (Released in 1999)
Excel 8.0	Excel 97 (Released in 1997)

 

IMEX=1 – Use this when you want to treat all your data in the file as text.

For example - >

Extended Properties="Excel 12.0 Xml;HDR=YES;IMEX=1";

To make the code to work properly you need to refer the Microsoft.Office.Interop.Excel assembly by adding a reference to your project.

1. using System;
2. using System.Data;
3. using System.Windows.Forms;
4. using System.Data.OleDb;
5. using Microsoft.Office.Interop.Excel;
7. namespace TestApp
8. {
9.     public partial class Form1 : Form
10.     {
11.         public Form1()
12.         {
13.             InitializeComponent();
14.         }
16.         private void button1_Click(object sender, EventArgs e)
17.         {
18.             openFileDialog1.ShowDialog();
19.             // Create an OLEDBConnection to connect to the Excel file.
20.             // I'm getting the required file by using a file dialog.
21.             // The @ symbol makes the string to contain any special characters inside the string without breaking the string.
22.             OleDbConnection dbConnection = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + openFileDialog1.FileName.ToString() + @";Extended Properties=""Excel 8.0;HDR=Yes;""");
23.             // Open the connection.
24.             dbConnection.Open();
25.             // Create a command object to work on the data.
26.             // Note that I have given the sheet name as [Sheet1$] to retrieve data from that named sheet in the particular Excel file.
27.             OleDbCommand dbCommand = new OleDbCommand("SELECT * FROM [Sheet1$]", dbConnection);
28.             // Creating a data reader to read data.
29.             OleDbDataReader dbReader = dbCommand.ExecuteReader();
30.             // If needed you can get the position of any column (e.g. Age), this will only work if you use HDR=Yes.
31.             int SearchingItem = dbReader.GetOrdinal("Age");
33.             // Create the Excel Application object.
34.             ApplicationClass ExcelApp = new ApplicationClass();
35.             // Set the visibility of the application.
36.             ExcelApp.Visible = true;
37.             // Create a new Excel Workbook.
38.             Workbook ExcelWorkbook = ExcelApp.Workbooks.Add(Type.Missing);
39.             // Create a new Excel Sheet.
40.             Worksheet ExcelSheet = (Worksheet)ExcelWorkbook.Sheets.Add(ExcelWorkbook.Sheets.get_Item(1), Type.Missing, 1, XlSheetType.xlWorksheet);
41.             // Will keep the current row index. This should start from 1 since the first row is 1.
42.             int CurrentRowIndex = 1;
43.             try
44.             {
45.                 // Read through the data.
46.                 while (dbReader.Read())
47.                 {
48.                     // Traverse through all the data columns.
49.                     for (int i = 0; i < dbReader.VisibleFieldCount; i++)
50.                     {
51.                         ExcelSheet.Cells[CurrentRowIndex, i + 1] = dbReader.GetValue(i);
52.                     }
53.                     CurrentRowIndex++;
54.                 }
55.                 // Save the Excel sheet.
56.                 // The @ symbol makes the string to contain any special characters inside the string without breaking the string.
57.                 ExcelApp.Save(@"C:\Projects\Ex.xls");
58.             }
59.             catch (Exception ex)
60.             {
61.                 MessageBox.Show(ex.ToString());
62.             }
63.         }
64.     }
65. }
66. 
    

Project has Stopped Working

If you create a .NET application to use SQL CE database when you try to run your application on a Windows Vista or Windows 7 machine you might get an error saying your application did stop working, and the error details might show that your are having a problem with System.Data.SQLServerCE.

The reason for this is that your system is not having the SQL Server CE runtime in your machine. To fix it what you need to do is to install the Microsoft SQL Server Compact 3.5 Service Pack 1 on your system. You can download it from the following Microsoft link.

http://www.microsoft.com/downloads/details.aspx?FamilyId=DC614AEE-7E1C-4881-9C32-3A6CE53384D9&displaylang=en

An error shown when you try to start the SharePoint Search service

After installing the SharePoint Server when you try to start the search service you might end up with the following error.

An unhandled exception occurred in the user interface.Exception Information: OSearch (Administrator)

or

An unhandled exception occurred in the user interface.Exception Information: OSearch (UserName)

If this comes don’t panic, what you need to do is when providing the username provide it with the full domain name. For example Domain.Local\Administrator.

You can find the Microsoft knowledge base article here.

Windows Mobile 7

Highly awaited Windows Mobile 7 is at last showing in horizon.

Have a glance at it by visiting the following URL.

http://www.microsoft.com/presspass/presskits/windowsphone/videoGallery.aspx?contentID=mobileworldcongress2010

http://www.microsoft.com/windowsmobile/en-us/cmpn/windowsphone7series/default.mspx

http://www.windowsphone7series.com/

Microsoft is planning to release phones with Windows Mobile 7 at the end of 2010.

How Networks Work

I found a really good video which explains how data is travelled in the network. This explains in simple words with animation about the tasks done by the following main components and more.

• Packet
• Router
• Switch
• Firewall

If anyone is interested in networking I highly recommend you to watch this.