Working with Asp.Net variables in c#

Variables don’t automatically maintain state across page calls in ASP.NET. Asp.Net Page has a life cycle and being stateless, the information is lost at the end of this cycle, after a request has been served on the client side. One way is to use View-state for the persistence of the variables, but this significantly increases the size of a page and the data sent and received, making it slow. There are several solution for this.

SessionState

hidden fields

querystrings

Here is SessionState example

// saving aHiddenVariable 
Session["aHiddenVariable"]="aHiddenVariable";

// retreiving aHiddenVariable 
string aHiddenVariable = (string)Session["aHiddenVariable"];

Here is hidden field example.

In HTML, we simply need to create:

<input type="hidden" id="aHiddenVariable">

To set it’s value in javascript:

document.getElementById("aHiddenVariable").value = "myValue"

In ASP.NET code-behind, you use the Request object to retrieve the value.

string aHiddenVariable= (string)Request.Params["aHiddenVariable"];

Here is a sample for QueryString

// setting quesryString
// set s=feed, "text" to search
http://codingphobia.com/?s=feed

// retrieve variable
string textToSearch= Request.QueryString["s"];

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Working with Files in c# – intoduction

Here are some of many classes available to work with files

using TextReder and TextWriter classes

string filePath = @"E:\TestDocument.txt";

// open file to read
TextReader tr = File.OpenText(filePath);
Console.WriteLine(tr.ReadToEnd());

// must close file after reading
tr.Close();

string filePath = @"E:\TestDocument.txt";

// open file to read
TextReader tr = File.OpenText(filePath);
Console.WriteLine(tr.ReadToEnd());

// must close file after reading
tr.Close();

using StreamReader and and StreamWriter classes

// open file to read file 
StreamReader sr = new StreamReader(filePath); 
Console.WriteLine(sr.ReadToEnd());

// must close file after writing
sr.Close();

// open file to write
StreamWriter sw = new StreamWriter(filePath);
sw.AutoFlush = true;
Console.WriteLine(sw.Encoding);
Console.WriteLine(sw.FormatProvider);
sw.WriteLine("Hello World");

// must close file after writing
sw.close()

Reading / writing To IsolatedStorageFile using IsolatedStorageFileStream

// declare file IsolatedStorageFile
IsolatedStorageFile isoStore = 
IsolatedStorageFile.GetUserStoreForAssembly();

// create file Stream
IsolatedStorageFileStream isoFS =
                new IsolatedStorageFileStream("temp.txt", FileMode.Create, FileAccess.Write);

// write to file
sw = new StreamWriter(isoFS);
sw.WriteLine("in iso storage" + "\n");           
sw.WriteLine("in iso storage FInished");

// must remember to close or the resouce is kept locked
sw.Close();

// read from IsolatedStorageFile
isoFS = new IsolatedStorageFileStream("temp.txt", FileMode.Open, FileAccess.Read);
sr = new StreamReader(isoFS);
Console.WriteLine(sr.ReadToEnd());

Working with Folder properties in C#

Here is a simple programs that evaluates different properties for a folder in Windows

class Folder : IComparable
    {
        public string name;
        public string path;
        public int size;
        public Folder(string _name, string _path, int _size)
        {
            name = _name;
            path = _path;
            size = _size;
        }

        #region IComparable Members

        public int CompareTo(object obj)
        {
            Folder folder = (Folder)obj;
            return folder.size.CompareTo(this.size);
        }

        #endregion
    }

class SizeClculator
    {
        public static ArrayList directories = new ArrayList();

        public static void GetFolders(string path)
        {
            DirectoryInfo di = new DirectoryInfo(path);
            if (di.GetDirectories().Length > 0)
            {
                foreach (DirectoryInfo dir in di.GetDirectories())
                {
                    GetFolders(dir.FullName);
                }
            }
            else
            {
                int size = 0;

                if (di.GetFiles().Length > 1)
                {
                    FileInfo[] fileInfo = di.GetFiles();
                    foreach (FileInfo fi in fileInfo)
                    {
                        size = size + (int)fi.Length;
                    }
                }
                directories.Add(new Folder(di.Name, di.FullName, size));
            }
        }
        public static ArrayList GetFoldersList()
        {
            return directories;
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            string filePath = @"D:\Common\Test";
            SizeClculator.GetFolders(filePath);
            ArrayList al = SizeClculator.GetFoldersList();
            al.Sort();
            foreach (Folder folder in al)
            {
                Console.WriteLine("Name:" +
                    "  || " + folder.name +
                    "  || Path: " + folder.path +
                    "  || Size: " + folder.size);
            }
            Console.ReadKey();
        }
    }

Working with StringBuilder in C#

This Post will look in to several Methods provided with StringBuilder class. There are several ways to declare and initialize an instance of StringBuilder class.

// declare StringBuilder instance
StringBuilder sb;

// default constructor
sb = new StringBuilder();

// new stringbuilder with initial capacity 
sb = new StringBuilder(10);

// new stringbuilder with with a new string
sb = new StringBuilder("codingphobia.com");

// initial with initial capacity
// and max limit over capacity
sb = new StringBuilder(10, 100);

// new stringbuilder with with a new string
// and max limit over capacity
sb = new StringBuilder("codingphobia.com", 1000);

// new stringbuilder with new string
// start index to place string
// length of string
//  max limit over capacity
sb = new StringBuilder("codingphobia.com", 10, 16, 1000);

Here are some of the built-in methods

// append string to stringbuilder
Console.WriteLine(sb.Append("First"));

// get current capacity
Console.WriteLine("current string capacity: " + sb.Capacity);

// compare string with stringbuilder
Console.WriteLine(sb.Equals("First"));

// get the hash code for the string builder
Console.WriteLine(sb.GetHashCode());

// get the type for the object
Console.WriteLine(sb.GetType());

// get the length for the string
Console.WriteLine(sb.Length);

// gt the capacity for stringbuilder
Console.WriteLine(sb.Capacity);

// gt the max capacity for stringbuilder
Console.WriteLine(sb.MaxCapacity);

// get the string anfd write to console
Console.WriteLine(sb);

// insert char at specific index
Console.WriteLine(sb.Insert(2, '-'));

// replace a char at specific index
Console.WriteLine(sb.Replace('-', ' '));

// remove a char from specific index
Console.WriteLine(sb.Remove(2, 1));

Following methods allows us to extend our stringbuilder with appending value at the end.

// Add string at the end of stringbuilder
sb.Append("new string");

// Add string with end of line at the end of stringbuilder
sb.AppendLine("new string");

// Add string at the end of stringbuilder, 
// with information about the format etc
sb.AppendFormat(new CultureInfo("en-US"),
                "# # # ### ##", new char[] { 'A', 'S', 'D', 'F' });

Following methods show how can we extend our string builder using insert method which has 18 overloads.
most common are as follows

 // insert char at 0 index 
 sb.Insert(0, '0');

 // insert bool at 0 index
 sb.Insert(0, true);

 // insert char Array at 0 index
sb.Insert(0, new char[] { '0', '1' });

// insert double value at 0 index
sb.Insert(0, 10.00);

// insert decimal value at 0 index
sb.Insert(0, 10);

// insert char Array value, from  index 2 to 3,
// at index 0 of string builder
sb.Insert(0, new char[] { '1', '2', '3', '4' }, 1, 1);

// insert string at 0 index
sb.Insert(0, "a String");