Csharp/CSharp Tutorial/Class/Properties

Add Length property to MyArray

<source lang="csharp">using System;

class MyArray {

 int[] a;
 int len;

 public bool errflag; 
  
 public MyArray(int size) { 
   a = new int[size]; 
   len = size;  
 } 

 public int Length { 
   get { 
     return len; 
   } 
 } 

 public int this[int index] { 
   get { 
     if(indexCheck(index)) { 
       errflag = false; 
       return a[index]; 
     } else { 
       errflag = true; 
       return 0; 
     } 
   } 

   set { 
     if(indexCheck(index)) { 
       a[index] = value; 
       errflag = false; 
     } 
     else errflag = true; 
   } 
 } 

 private bool indexCheck(int index) { 
  if(index >= 0 & index < Length) 
     return true; 
  return false; 
 } 

}

class MainClass {

 public static void Main() {  
   MyArray myArray = new MyArray(5); 
   int x; 

   for(int i=0; i < myArray.Length; i++) 
     myArray[i] = i*10; 

   for(int i=0; i < myArray.Length; i++) { 
     x = myArray[i]; 
     if(x != -1) Console.Write(x + " "); 
   } 
   Console.WriteLine(); 
 } 

}</source>

0 10 20 30 40

Add statement to the getter and setter of a property

<source lang="csharp">public class A {

  private int myValue;
  public int MyValue
  {
     get
     {
        System.Console.WriteLine( "Getting myValue" );
        return myValue;
     }
     set
     {
        System.Console.WriteLine( "Setting myValue" );
        myValue = value;
     }
  }

} public class MainClass {

  static void Main()
  {
     A obj = new A();
     obj.MyValue = 1;
     System.Console.WriteLine( "obj.Value = {0}",
                               obj.MyValue );
  }

}</source>

Setting myValue
Getting myValue
obj.Value = 1

A simple property example

<source lang="csharp">using System;

class SimpProp {

 int prop; 

 public SimpProp() { 
    prop = 0; 
 } 

 public int MyProp { 
   get { 
     return prop; 
   } 
   set { 
     prop = value; 
   }  
 } 

}

class MainClass {

 public static void Main() {  
   SimpProp ob = new SimpProp(); 

   Console.WriteLine("Original value of ob.MyProp: " + ob.MyProp); 

   ob.MyProp = 100;
   Console.WriteLine("Value of ob.MyProp: " + ob.MyProp); 

   Console.WriteLine("Attempting to assign -10 to ob.MyProp"); 
   ob.MyProp = -10; 
   Console.WriteLine("Value of ob.MyProp: " + ob.MyProp); 
 } 

}</source>

Original value of ob.MyProp: 0
Value of ob.MyProp: 100
Attempting to assign -10 to ob.MyProp
Value of ob.MyProp: -10

Combine readonly and read only property

<source lang="csharp">using System; public sealed class Value {

   public int intValue = 10;

} public sealed class MyController {

   public MyController( Value pimpl ) {
       this.pimpl = pimpl;
   }
   public int IntValue {
       get {
           return pimpl.intValue;
       }
   }
   private readonly Value pimpl;

} public sealed class MainClass {

   static void Main() {
       Value someNumber = new Value( );
   }

}</source>

Define accessors for Properties with get and set

<source lang="csharp">class MyClass {

   private string name;
   
   public string Name
   {
       get 
       {
           return name;
       }
       set 
       {
           name = value;
       }
   }

}</source>

Do calculation with Property

<source lang="csharp">using System; public class SomeClass {

   private int num;
   public SomeClass(int i)
   {
       num = i;
   }
   public int Num
   {
       get { return num; }
       set { num = value; }
   }

}

public class CompoundAssPropApp {

   public static void Main(string[] args)
   {
       SomeClass sc = new SomeClass(42);
       Console.WriteLine("{0}", sc.Num);
       
       sc.Num = sc.Num + 5;
       Console.WriteLine("{0}", sc.Num);
   }

}</source>

Invoke Indexed Property Demo

<source lang="csharp">using System; using System.Reflection; using System.Globalization;

 class Class1
 {
 
 
   DateTime[] dateTimes = new DateTime[10];
   public DateTime this[int index]
   {
     get{ return dateTimes[index]; }
     set{ dateTimes[index] = value;}
   }
   
   
   private DateTime dateOfBirth;
   public DateTime DateOfBirth
   {
       get{ return dateOfBirth; }
       set{ dateOfBirth = value; }
   }
     
   public void Test()
   {
     Console.WriteLine("Test method called");
   }
   
   
   private string field;
   
   public string Property
   { 
     get{ return field; }
     set{ field = value; }
   }
   
 }

   class MainClass{
   
   static void Main(string[] args)
   {
     Type type = typeof(Class1);
     Console.WriteLine(type.FullName);
     
     object o = Activator.CreateInstance(type);
     type.InvokeMember( "Item", 
       BindingFlags.Instance | 
       BindingFlags.SetProperty | BindingFlags.Public, 
       null, o, new object[]{0, new DateTime(1966, 2, 12)});
       
     Console.WriteLine(((Class1)o)[0].ToString());
   }
   }</source>

Properties and its Restrictions

1. A property consists of a name along with get and set accessors.
2. The accessors are used to get and set the value of a variable.

The general form of a property is shown here:

<source lang="csharp">type propertyName {

       get {
           // get accessor code
       }
       
       set {
           // set accessor code
       }
   }</source>

1. A property cannot be passed as a ref or out parameter to a method.
2. You cannot overload a property.
3. A property should not alter the state of the underlying variable when the get accessor is called.

(Quote from C# The Complete Reference, Publisher: Osborne/McGraw-Hill, March 8, 2002, Language: English ISBN-10: 0072134852 ISBN-13: 978-0072134858)

Property And its associated Field

<source lang="csharp">using System;

class MyClass {

  private int privateInnerValue = 10; 
  public int MyValue                  
  {
     set { 
        privateInnerValue = value; 
     }
     get { 
        return privateInnerValue; 
     } 
  }

} class MainClass {

  static void Main()
  {
     MyClass c = new MyClass();
     Console.WriteLine("MyValue: {0}", c.MyValue);
     c.MyValue = 20;
     Console.WriteLine("MyValue: {0}", c.MyValue);
  }

}</source>

MyValue: 10
MyValue: 20

Property Getter and Setter

<source lang="csharp">using System;

class Address {

   protected string city;
   public string City
   { 
    get { return city; }
   }
  
   protected string zipCode;
   public string ZipCode
   {
       get { return zipCode; }
       set 
       { 
           zipCode = value; 
           city = "Atlanta";
       }
   }

}

class PropertyApp {

   public static void Main()
   {
       Address addr = new Address();
       addr.ZipCode = "30338";
       string zip = addr.ZipCode;
  
       Console.WriteLine("The city for ZIP code {0} is {1}", addr.ZipCode, addr.City);
   }

}</source>

Put logic to property setter

<source lang="csharp">using System; using System.Collections.Generic; using System.Text; class MainClass {

   static void Main(string[] args)
   {
       Person person = new Person();
       person.SetName("A", "B");
       Console.WriteLine("The person"s full name is {0}",person.FullName);
       person.FullName = "A b c";
       Console.WriteLine("The person"s full name is {0}",person.FullName);
   }

} class Person {

   private string _lastname;
   private string _firstname;
   public void SetName(string lastname, string firstname)
   {
       _lastname = lastname;
       _firstname = firstname;
   }
   public string FullName
   {
       get
       {
           return _firstname + " " + _lastname;
       }
       set
       {
           string[] names = value.Split(new string[] { " " },StringSplitOptions.RemoveEmptyEntries);
           _firstname = names[0];
           _lastname = names[names.Length - 1];
       }
   }

}</source>

The person"s full name is B A
The person"s full name is A c

Readonly property

<source lang="csharp">using System; class MyClass {

  public double A = 3;
  public double B = 4;
  
  public double MyValue                            
  {
     get { return A * B ; }     
  }

} class MainClass {

  static void Main()
  {
     MyClass c = new MyClass();
     Console.WriteLine("MyValue: {0}", c.MyValue);
  }

}</source>

MyValue: 12

throw Exception from property setting

<source lang="csharp">using System; using System.Collections.Generic; using System.Linq; using System.Text;

   public class MyClass
   {
       public readonly string Name;
       private int intVal;
       public int Val
       {
           get
           {
               return intVal;
           }
           set
           {
               if (value >= 0 && value <= 10)
                   intVal = value;
               else
                   throw (new ArgumentOutOfRangeException("Val", value,"Val must be assigned a value between 0 and 10."));
           }
       }
       public override string ToString()
       {
           return "Name: " + Name + "\nVal: " + Val;
       }
       private MyClass() : this("Default Name")
       {
       }
       public MyClass(string newName)
       {
           Name = newName;
           intVal = 0;
       }
   }
   class Program
   {
       static void Main(string[] args)
       {
           MyClass myObj = new MyClass("My Object");
           Console.WriteLine("myObj created.");
           for (int i = -1; i <= 0; i++)
           {
               try
               {
                   myObj.Val = i;
               }
               catch (Exception e)
               {
                   Console.WriteLine("Exception {0} thrown.", e.GetType().FullName);
                   Console.WriteLine("Message:\n\"{0}\"", e.Message);
               }
           }
       }
   }</source>

Use properties to set and get private members.

<source lang="csharp">using System;

class Shape {

 double pri_width;  // now private 
 double pri_height; // now private  

 // Properties for width and height. 
 public double width { 
    get { return pri_width; } 
    set { pri_width = value; } 
 } 

 public double height { 
    get { return pri_height; } 
    set { pri_height = value; } 
 } 

 public void showDim() { 
   Console.WriteLine("Width and height are " + 
                      width + " and " + height); 
 } 

}

class Triangle : Shape {

 public string style; // style of triangle 
  
 public double area() { 
   return width * height / 2;  
 } 

 public void showStyle() { 
   Console.WriteLine("Triangle is " + style); 
 } 

}

class MainClass {

 public static void Main() { 
   Triangle t1 = new Triangle(); 
   Triangle t2 = new Triangle(); 

   t1.width = 4.0; 
   t1.height = 4.0; 
   t1.style = "isosceles"; 

   t2.width = 8.0; 
   t2.height = 12.0; 
   t2.style = "right"; 

   Console.WriteLine("Info for t1: "); 
   t1.showStyle(); 
   t1.showDim(); 
   Console.WriteLine("Area is " + t1.area()); 

   Console.WriteLine(); 

   Console.WriteLine("Info for t2: "); 
   t2.showStyle(); 
   t2.showDim(); 
   Console.WriteLine("Area is " + t2.area()); 
 } 

}</source>

Info for t1:
Triangle is isosceles
Width and height are 4 and 4
Area is 8
Info for t2:
Triangle is right
Width and height are 8 and 12
Area is 48