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Indexers C#

C# > Indexers

Indexers enable to create a class that client applications can access as an array.

Implementation: encapsulate an internal collection or array.

Example:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1

{
    public partial class Form1 : Form
    {
        class Test
        {
            private string[] mStr = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "K"};
            public int Length
            {
                get { return mStr.Length; }
            }
            // Indexer declaration.
            public string this[int index]
            {
                get
                {
                    return mStr[index];
                }
                set
                {
                    mStr[index] = value;
                }
            }
        }
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Test t = new Test();
            //  indexer set accessor
            t[1] = "a";
            t[2] = "b";
            //  indexer get accessor
            for (int i = 0; i < t.Length -1 ; i++)
            {
                MessageBox.Show(t[i]); 
            }
        }
     }
}

 

Asc Method Visual Basic

VB.NET > Functions > ASC

Asc Method returns an Integer value of character code corresponding to a character.

Example:

Dim IntCode As Integer
IntCode = Asc("A") '65
IntCode = Asc("a") '97
IntCode = Asc("@") '64
IntCode = Asc("?") '93

CType Function Visual Basic NET

VB.NET > Functions > CType

CType function returns the result of explicitly converting an expression to a specified data type.

Example:

Public Class Form1

  Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Dim mStr As String = "100"
    Dim mInt As Integer = CType(mStr, Integer) 'convert "100" string to mInt = 100 OK

    mStr = "aaa"
    mInt = CType(mStr, Integer) ' Error: Conversion from string "aaa" to type 'Integer' is not valid. NOK
  End Sub
End Class

Events C#

Events in C# are based on the delegate model.

To declare an event in a class the delegate type for the event must be declared.

Events use the publisher-subscriber model.

A publisher is an object that contains the definition of the event and the delegate.
A subscriber is an object that accepts the event and provides an event handler.




Example:

using System;

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1

{
    public partial class Form1 : Form
    {
        public class Event
        {
            private int value;
            public delegate void EventHandler(int v);
            public event EventHandler ValueChanged;

            protected virtual void OnValueChanged()
            {
                if (ValueChanged != null)
                {
                    ValueChanged(value);
                }
            }
            public Event()
            {
            }
            public void SetValue(int n)
            {
                if (value != n)
                {
                     value = n;
                    OnValueChanged(); // raise event
                }
            }
        }
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Event ev = new Event();
            ev.ValueChanged += ev_ValueChanged;
            ev.SetValue(2);
            ev.SetValue(3);
        }
        void ev_ValueChanged(int v)
        {
           MessageBox.Show("Event value : " + v.ToString()); 
        }
     }
}

 

Logger class Delegate Example

C# > Delegate

Logger class Delegate Example

Example:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1

{
    public partial class Form1 : Form
    {
        public class LoggerClass
        {
            public delegate void LogHandler(string message); // Declare a delegate
            public void Log(LogHandler vLogHandler)
            {
                vLogHandler("Log begin");
                // do stuff ...
                vLogHandler("Log end");
            }
        }
        static void Logger(string s)
        {
            MessageBox.Show(s);
        }
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            LoggerClass mClass = new LoggerClass();
            LoggerClass.LogHandler mLogger = new LoggerClass.LogHandler(Logger);  // create an instance of the delegate and pointing to the logging function.
            mClass.Log(mLogger); // delegate will be passed to the Log() function.
        }
    }
}

Square brackets ([]) operator C#

C# > Operators > [] Operator 

Square brackets ([]) operator is used for arrays, indexers, and attributes.

Examples
 //arrays
  int[] mList;
  mList = new int[200];

 //indexers
  System.Collections.Hashtable h = new System.Collections.Hashtable();
  h["e1"] = 1;
      
  //attributes
  [System.Serializable]