diff between variable and property? [duplicate]

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What is the difference between a field and a property in C#?

i would like 开发者_JAVA百科to know the difference between a variable and a property.can any one explain

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A property is actually a special function with a get method and a set method. The get and set methods can provide some logic, like validation that a field can not.

You can back your property with a private field, like this

private int age;

public int Age
{
    get { return age; }
    set
    {
        if (value < 0)
             throw new ArgumentException("Must be > 0");
        age = value;
    }
}

You can also implement only the get part and calculate the result

private int a;
private int b;

public int Sum
{
    return a + b;
}

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Simply you can't validate the data being stored in variable but in a Property you can. A Propery is more like a method as it has get & set methods which you define to handle the data.

Also they are usefull in Databinding.

Properties expose fields. Fields should (almost always) be kept private to a class and accessed via get and set properties. Properties provide a level of abstraction allowing you to change the fields while not affecting the external way they are accessed by the things that use your class.

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Example:

like in case of Date of Birth. You need to validate that age is less then todays date:

In a Field this is valid:

DateTime age = new DateTime(2012,12,1);//1 december 2012

But in a property you can validate it:

private DateTime _dob;
public DateTime dob
{
    get
    {
        if(_dob!= null) return _dob;
    }
    set
    {
        if(DateTime.Compare(value, DateTime.Today) <= 0)
        {
             _dob= value;
        }
        else
        {
               throw new System.InvalidOperationException("Date of Birth should be less then today's date");
        }
    }
}

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A property or "auto property" is just an easier way to write the complete implementation. It's a way to make code more readable and more manageable.

A field in C# inside your class outside of methods might look like this:

private object _obj;

However if you want to "expose" this to other classes that uses your class you don't just want to make it public. Because that would not give you any control over what values it is set to.

Therefore you might want to have a getter and a setter for this particular field.

One way to implement this, and a quite common way in most other languages is to have two methods:

Getter

public object getObj() { return _obj; }

Setter

public void setObj(object value) { _obj = value; }

However doing this for all of your fields makes a lot of lines that you wouldn't really need, this is a trivial problem and therefore C# will help you out by giving you a way of defining "properties".

Properties in C# 1.0

In C# 1.0 you wrote a property like this:

private object _obj;
public object Obj
{
    get { return _obj; }
    set { _obj = value; }
}

You still needed the private field though, which is still an overhead.

Properties in C# 2.0 and onwards

In later versions of C# you could make it easier for yourself, in C# 2.0 you could write something like this:

public object Obj { get; set; }

Which would auto-generate the above in your IL which in the end would end up looking the same as the first example when using methods.

In C# 3.0 an issue was solved, how do you create a public getter but a private setter?

Nowdays you can write it like this:

public object Obj { get; private set; }

Which will let you expose the object, but make it read only! ( not true read only since you can manipulate it inside your class ).

So simply explained, a field is a variable exposed inside or outside your class, but you have no way of controlling the values that someone with direct access to it decides to set it to.

A property is a way to expose setters / getters to your fields, making it easier to manage input / output to and from your field.