Properties vs Methods

Question

Quick question: When do you decide to use properties (in C#) and when do you decide to use methods?

We are busy having this debate and have found some areas where it is debatable whether we should use a property or a method. One example is this:

public void SetLabel(string text)
{
    Label.Text = text;
}

In the example, Label is a control on a ASPX page. Is there a principle that can govern the decision (in this case) whether to make this a method or a property.

I'll accept the answer that is most general and comprehensive, but that also touches on the example that I have given.

Answer 1

I think the semantic difference should be seen as the following: a property is literally a property of the object; whereas a method is an action to perform.

In cases where the action you are taking is to get or change a value, yet the value that you are getting or changing is not semantically a property of the object performing those actions, then you should use methods and not a property. Using a property would be semantically incorrect.

Answer 2

This is simple.

1: use property when you want your data should be validated before storing in field. So in this way property provides encapsulation for your fields. Because if you leave your fields public end user may assign any value which may or may not be valid as per your business requirement like age should be greater than 18. So before value is store corresponding field we need to check its validity. In this way properties represent data.

2: Use method when you want perform some action like you are supplying some data as parameter and your method is doing some processing on the basis of supplied values and returning processed value as output. Or you want to change value of some field by this calculation. "In this way method represents action".

Answer 3

From the Choosing Between Properties and Methods section of Design Guidelines for Developing Class Libraries:

In general, methods represent actions and properties represent data. Properties are meant to be used like fields, meaning that properties should not be computationally complex or produce side effects. When it does not violate the following guidelines, consider using a property, rather than a method, because less experienced developers find properties easier to use.

Answer 4

Here is a good set of guidelines for when to use properties vs methods from Bill Wagner

• Use a Property when all these are true: The getters should be simple and thus unlikely to throw exceptions. Note that this implies no network (or database) access. Either might fail, and therefore would throw an exception.
• They should not have dependencies on each other. Note that this would include setting one property and having it affect another. (For example, setting the FirstName property would affect a read-only FullName property that composed the first name + last name properties implies such a dependency )
• They should be settable in any order
• The getter does not have an observable side effect Note this guideline doesn't preclude some forms of lazy evaluation in a property.
• The method must always return immediately. (Note that this precludes a property that makes a database access call, web service call, or other similar operation).
• Use a method if the member returns an array.
• Repeated calls to the getter (without intervening code) should return the same value.

• Repeated calls to the setter (with the same value) should yield no difference from a single call.

• The get should not return a reference to internal data structures (See item 23). A method could return a deep copy, and could avoid this issue.

*Taken from my answer to a duplicate question.

Answer 5

Also big plus for Properties is that value of property can be seen in Visual Studio during debugging.

Answer 6

I come from java an i used get.. set.. method for a while.

When i write code, i don't ask to my self: "accessing this data is simple or require a heavy process?" because things can change (today retrive this property is simple, tomonrow can require some or heavy process).

Today i have a method SetAge(int age) tomonrow i will have also method SetAge(date birthdate) that calculate the age using the birthdate.

I was very disappointed that the compiler transform property in get and set but don't consider my Get... and Set.. methods as the same.

Answer 7

Searching through MSDN, I found a reference on Properties vs Methods that provides some great guidelines for creating methods:

• The operation is a conversion, such as Object.ToString.
• The operation is expensive enough that you want to communicate to the user that they should consider caching the result.
• Obtaining a property value using the get accessor would have an observable side effect.
• Calling the member twice in succession produces different results.
• The order of execution is important. Note that a type's properties should be able to be set and retrieved in any order.
• The member is static but returns a value that can be changed.
• The member returns an array. Properties that return arrays can be very misleading. Usually it is necessary to return a copy of the internal array so that the user cannot change internal state. This, coupled with the fact that a user can easily assume it is an indexed property, leads to inefficient code.

Answer 8

As a matter of design Properties represent Data or Attributes of class object, While methods are actions or behaviors of class object.

In .Net, world there are other implications of using Properties:

• Properties are used in Databinding, while get_ / set_ methods are not.
  
• XML serialization user properties as natural mechanism of serilization.
  
• Properties are accessed by PropertyGrid control and intern ICustomTypeDescriptor, which can be used effectively if you are writing a custom library.
  
• Properties are controlled by Attributes, one can use it wisely to design Aspect Oriented softwares.

Misconceptions (IMHO) about Properties' usage:

• Used to expose small calculations: ControlDesigner.SelectionRules's get block runs into 72 lines!!
  
• Used to expose internal Data structures: Even if a property does not map to an internal data member, one can use it as property, if its an attribute of your class. Viceversa, even if its an attribute of your class properties are not advisable, to return array like data members (instead methods are used to return deep copy of members.)

In the example here it could have been written, with more business meaning as:

public String Title
{
    set { Label.Text = text; }
}

Answer 9

Symantically properties are attributes of your objects. Methods are behaviors of your object.

Label is an attribute and it makes more sense to make it a property.

In terms of Object Oriented Programming you should have a clear understanding of what is part of behavior and what is merely an attribute.

Car { Color, Model, Brand }

A car has Color, Model and Brand attributes therefore it does not make sense to have a method SetColor or SetModel because symantically we do not ask Car to set its own color.

So if you map the property/method case to the real life object or look at it from symantic view point, your confusion will really go away.

Answer 10

You need only look at the very name... "Property". What does it mean? The dictionary defines it in many ways, but in this case "an essential or distinctive attribute or quality of a thing" fits best.

Think about the purpose of the action. Are you, in fact, altering or retrieving "an essential or distinctive attribute"? In your example, you are using a function to set a property of a textbox. That seems kind of silly, does it not?

Properties really are functions. They all compile down to getXXX() and setXXX(). It just hides them in syntactic sugar, but it's sugar that provides a semantic meaning to the process.

Think about properties like attributes. A car has many attributes. Color, MPG, Model, etc.. Not all properties are setable, some are calculatable.

Meanwhile, a Method is an action. GetColor should be a property. GetFile() should be a function. Another rule of thumb is, if it doesn't change the state of the object, then it should be a function. For example, CalculatePiToNthDigit(n) should be a function, because it's not actually changing the state of the Math object it's attached to.

This is maybe rambling a bit, but it really boils down to deciding what your objects are, and what they represent. If you can't figure out if it should be a property or function, maybe it doesn't matter which.

Answer 11

Properties are a way to inject or retrieve data from an object. They create an abstraction over variables or data within a class. They are analogous to getters and setters in Java.

Methods encapsulate an operation.

In general I use properties to expose single bits of data, or small calculations on a class, like sales tax. Which is derived from the number of items and their cost in a shopping cart.

I use methods when I create an operation, like retrieving data from the database. Any operation that has moving parts, is a candidate for a method.

In your code example I would wrap it in a property if I need to access it outside it's containing class:

public Label Title 
{
   get{ return titleLabel;}
   set{ titleLabel = value;}
}

Setting the text:

Title.Text = "Properties vs Methods";

If I was only setting the Text property of the Label this is how I would do it:

public string Title 
{
   get{ return titleLabel.Text;}
   set{ titleLabel.Text = value;}
}

Setting the text:

Title = "Properties vs Methods";

Answer 12

I only use properties for variable access, i.e. getting and setting individual variables, or getting and setting data in controls. As soon as any kind of data manipulation is needed/performed, I use methods.

Answer 13

Properties are really nice because they are accessible in the visual designer of visual studio, provided they have access.

They use be used were you are merely setting and getting and perhaps some validation that does not access a significant amount of code. Be careful because creating complex objects during validation is not simple.

Anything else methods are the preferred way.

It's not just about semantics. Using properties inappropriate start having weirdness occur in the visual studio visual designer.

For instance I was getting a configuration value within a property of a class. The configuration class actually opens a file and runs an sql query to get the value of that configuration. This caused problems in my application where the configuration file would get opened and locked by visual studio itself rather than my application because was not only reading but writing the configuration value (via the setter method). To fix this I just had to change it to a method.

Answer 14

If you're setting an actual property of your object then you use a property.

If you're performing a task / functionality then you use a method.

In your example, it is a definite property being set.

If however, your functionality was to AppendToLabel then you would use a method.

Answer 15

Properties should only be simple set and get one liners. Anything more and it should really be moved to a method. Complex code should always be in methods.

Answer 16

I prefer to use properties for add/set methods with 1 parameter. If parameters are more, use methods.

Answer 17

Yes, if all you're doing is getting and setting, use a property.

If you're doing something complex that may affect several data members, a method is more appropriate. Or if your getter takes parameters or your setter takes more than a value parameter.

In the middle is a grey area where the line can be a little blurred. There is no hard and fast rule and different people will sometimes disagree whether something should be a property or a method. The important thing is just to be (relatively) consistent with how you do it (or how your team does it).

They are largely interchangeable but a property signals to the user that the implementation is relatively "simple". Oh and the syntax is a little cleaner.

Generally speaking, my philosophy is that if you start writing a method name that begins with get or set and takes zero or one parameter (respectively) then it's a prime candidate for a property.