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Difference between Property and Field in C# .NET 3.5+
What's the difference between using
public string Username { get; set; }
and using
public string Username;
I have always been using the first one, but wanted to understand if there is any difference between the two, and scenarios when one should prefer over the other.
public string Username { get; set; }
is a Property.
while
public string Username;
is a Public variable.
For more comparison,
Reflection works differently on variables vs. properties, so if you rely on reflection, it's easier to use all properties.
You can't databind against a variable.
Changing a variable to a property is a breaking change.
Other link
Properties vs. Public Variables
One thing you can do with properties that you can't do with fields is limit visibility for either setter or getter:
public string MyProperty { get; private set; }
Something I use quite a lot.
And something (more powerful) you can't do with fields is define them inside an interface. Suppose you want an interface that requires implementing classes to have a certain property:
public interface MyInterface
{
string MyProperty { get; }
}
Note that you do not need to have a setter here. It is entirely up to implementing classes to determine how they should set MyProperty.
Here is a very small example of one way you could use a string property over simply using a string.
Say you have a private variable called:
private string _name;
Now lets say you wanted to make that string read only? In other words, you can't change the value. You could use the following:
public string Name
{
get { return _name; }
}
It can allow you to control access to that value. Alternatively, you can have it so that that variable can only be write only doing the following:
public string Name
{
set { _name = value; }
}
Now if you put it together, it will allow you to set to value or simply get the value. See the following:
public string Name
{
get { return _name; }
set { _name = value; }
}
You may be wondering what the point of that is since it looks like you can do the same thing with a regular string, well of course but this controls direct access to the _name variable from outside classes that aren't derived from said class.
Now what if you wanted to control how that value is set? What if you want to do some calculation or perhaps you wanted to add a prefix or suffix to that value? You do the following:
public string Name
{
get
{
return _name;
}
set
{
if (value.ToLower() == "bilbo")
_name = "Bilbo Baggins";
}
}
Now, if you set the Name property of the class to bilbo, the value of _name will be set to Bilbo Baggins as opposed to if you set the property to Amy, the _name variable will contain simply, amy.
You can do this to guarantee that whatever value that the property is set to is automatically upper or lowercase, or perhaps you can do some validation on the value or something of that sort.
I hope this explains the uses of properties and how they can be useful without making it too complicated.
Properties provide you with more flexibility, especially in .NET. C# shows bias toward properties, so keep that in mind. However, as a general rule, use accessors/mutators when getting or setting needs "processing" or an accompanying action. Use fields for holding values. E.g.,
public class Name
{
public string First;
public string Last;
public string Full{ get { return this.First + " " + this.Last; } }
}
Related
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What is the difference between a field and a property?
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So this is one of my first classes for Object-Oriented Development and my feedback for my code was that I was missing "a property" and that GetName() is a method rather than a property. I'm currently coding in c# and was wondering if anyone could explain what a property is or point me in the right direction I'd be very appreciative.
//Instance Variables
private String name;
private decimal balance;
//Variables
public AccountDetails(String name, decimal balance)
{
this.name = name;
this.balance = balance;
}
//Accessor Methods
public String GetName()
{
return this.name;
}
You could have replaced your method with property like
public string Name { get { return this.name; } }
There is basically no difference between methods and properties. Getters and setters get internally translated into standard methods such that the runtime has no idea whether some getter or setter is associated with a certain property.
However, there is an important software engineering benefit: your code tends to be easier to understand if you restrict yourself to use getters and setters with get and set semantics. I.e. do only the steps necessary to provide the respective property.
https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/properties
GeeName() is a method, could be called Getter in Java. Properties in C# work a bit differently, the declaration goes like
//no direct variable declaration
public String Name1 { get; set; }
//with variable declaration and custom getter logic
//notice, that properties don't need to implement both GET and SET (but they can)
private String _name;
private int _access_counter = 0;
public String Name2
{
get
{
_access_counter++;
return _name + _access_counter;
}
}
public String Name3
{
set
{
_access_counter--;
_name = value;
}
}
Consider the following code:
private string _text = null;
private string[] _values = null;
public string Text { get { return _text; } }
public string[] Values { get { return _values; } }
What does this accomplish that having the public members alone would not?
By using properties instead of public fields, you hide the implementation.
If at some point you need to change what the Text and Values properties return, you can change the behavior without changing the API of the class.
Additionally, this idiom limits external access to the exposed data as read-only.
It's to make values readonly, though I'd be more inclined to write it like this:
public string Text { get; private set;}
public string[] Values { get; private set; }
This code would allow external entities to read your values, while your code internally could modify the backing field.
You can short-hand that using auto-properties:
public string Text { get; private set; }
public string[] Values { get; private set; }
With a public field, you would not be able to protect against external modification and support internal modification at the same time.
Even if you want to expose a field as writeable externally, I would still suggest encapsulating the thing in a property - you never know if you need to support something internally without breaking the external contract (custom code in the set/get gives you space to do this).
Not to mention most data binding frameworks do not see fields, only properties.
The _text and _values can only be set within the class that they are defined, but their values can be accessed via the properties.
In your example its making the properties as read only, but there are other uses as well.
public string Text { get { return _text; } }
If you want to do some operation internally on the return_text and then return it against proeperty Text you could something like.
public string Text { get { return _text.ToUpper(); } }
This is field Encapsulation
Encapsulation is sometimes referred to as the first pillar or
principle of object-oriented programming. According to the principle
of encapsulation, a class or struct can specify how accessible each of
its members is to code outside of the class or struct. Methods and
variables that are not intended to be used from outside of the class
or assembly can be hidden to limit the potential for coding errors or
malicious exploits.
Consider the following example:
// private field
private DateTime date;
// Public property exposes date field safely.
public DateTime Date
{
get
{
return date;
}
set
{
// Set some reasonable boundaries for likely birth dates.
if (value.Year > 1900 && value.Year <= DateTime.Today.Year)
{
date = value;
}
else
throw new ArgumentOutOfRangeException();
}
}
In this example there is a private field date which is exposed publicly through property Date. Now if you want to set the boundary for date then you can see the set part of the property.
I learned c# recently, so when I learned to write properties, I was taught to do it like this:
public string Name { get; set; }
Auto properties are great! But now I'm trying to do something a little more complicated, so I need to write a custom pair of accessors.
private string _Name;
public string Name {
get { return _Name; }
set { _Name = value }
}
I know the compiler makes a private instance variable down in it's murky depths when one uses autos, but I'm spoiled and don't want that private variable sitting around looking pointless.
Is there a way to use custom accessors without a private variable?
Properties don't need backing variables (fields) at all. While they can be used for encapsulating simple fields you can also use them to access other data.
public Decimal GrandTotal { get { return FreightTotal + TaxTotal + LineTotal; } }
or
public string SomeStatus { get { return SomeMethodCall(); } }
If the goal is to simply encapsulate some field with a property you would need some sort of backing field if you are not using automatic properties.
The answer is No, you cannot do that.
It is because of recursion. (See line numbers 9 and 7):
Line 1 : public string Name
Line 2 : {
Line 3 : get
Line 4 : {
Line 5 : return FirstName + " " + LastName;
Line 6 : }
Line 7 : set
Line 8 : {
Line 9 : Name = value; // <-- Goes back to Line 7
Line 10 : }
Line 11 : }
No, I'm afraid not. The compiler is smart enough to make this happen for you on auto-generated properties, but with standard properties I imagine the logic behind something like that would end up getting in the way and doing more harm than good.
For example, what if I create a property like this...
public int SomeValue
{
get
{
return 0;
}
}
Would the compiler (with the feature you're looking for) create a backing private variable? Why? It doesn't need one.
Additionally, if the private value isn't created until compilation time, what are you going to reference in your code:
public string Name {
get { return _Name; }
set { _Name = value }
}
What is _Name? What if you have another value somewhere else called _Name? Then what would the compiler call the backing value for this property? What if I need two backing values? Would the compiler be smart enough for that?
public string Name
{
get
{
return string.Format("{0} {1}", _FirstName, _LastName);
}
set
{
// some parsing magic
}
}
It's been asked before, but I imagine the answer is going to continue to be "no" for the foreseeable future.
An auto-property is syntactic shorthand for simple direct member access. (And I imagine one of its driving forces was simply to try to get people to stop creating public values directly.) Properties can grow in complexity well beyond that very easily and I personally wouldn't want the compiler trying to figure out what I can easily just tell it to do.
I know this is an old question, but there is at least one other option here. I'm doing something similar to the below for my own app.
This might not exactly be for your use case, but it shows that a custom getter and setter can be used without a private instance variable. In this case, the getter and setter are shortcut or helper methods to access the Name property of the User for the Account.
We can let the value be set by doing Account.AccountUser.Name = "John Doe";, but sometimes that seems a bit clunky and it works against the idea of separation of concerns. Do we want someone using the Account class to know there's a User imbedded in it? If for some reason we don't, we now have a way to still update the User.Name even if we make AccountUser private.
In this case, AccountUser is public, but it doesn't have to be. When it's private, a Json or XML conversion utility (such as Newtonsoft) should ignore the AccountUser and show just the Name as if the Account were a flat model, instead of having multiple levels.
public class User
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Account
{
public int Id { get; set; }
public User AccountUser { get; set; }
public string Name
{
get
{
return AccountUser.Name;
}
set
{
AccountUser.Name = value;
}
}
}
I'm taking a C# class right now and I'm trying to find out the best way of doing things. I come from a Java background and so I'm only familiar with Java best-practices; I'm a C# novice!
In Java if I have a private property, I do this;
private String name;
public void setName(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
In C#, I see that there are many ways of doing this.
I can do it like Java:
private string name;
public void setName(string name) {
this.name = name;
}
public string getName() {
return this.name;
}
Or I can do it this way:
private string name;
public string Name {
get { return name; }
set { name = value; }
}
Or:
public string Name { get; set; }
Which one should I use, and what are the caveats or subtleties involved with each approach? When creating classes, I am following general best-practices that I know from Java (especially reading Effective Java). So for example, I am favoring immutability (providing setters only when necessary). I'm just curious to see how these practices fit in with the various ways of providing setters and getters in C#; essentially, how would I translate best-practices from the Java world into C#?
EDIT
I was posting this as a comment to Jon Skeet's answer but then it got long:
What about a non-trivial property (i.e., with significant processing and validation perhaps)? Could I still expose it via a public property but with the logic encapsulated in get and set? Why would/should I do this over having dedicated setter and getter methods (with associated processing and validation logic).
Pre-C# 6
I'd use the last of these, for a trivial property. Note that I'd call this a public property as both the getters and setters are public.
Immutability is a bit of a pain with automatically implemented properties - you can't write an auto-property which only has a getter; the closest you can come is:
public string Foo { get; private set; }
which isn't really immutable... just immutable outside your class. So you may wish to use a real read-only property instead:
private readonly string foo;
public string Foo { get { return foo; } }
You definitely don't want to write getName() and setName(). In some cases it makes sense to write Get/Set methods rather than using properties, particularly if they could be expensive and you wish to emphasize that. However, you'd want to follow the .NET naming convention of PascalCase for methods, and you wouldn't want a trivial property like this to be implemented with normal methods anyway - a property is much more idiomatic here.
C# 6
Hooray, we finally have proper read-only automatically implemented properties:
// This can only be assigned to within the constructor
public string Foo { get; }
Likewise for read-only properties which do need to do some work, you can use member-bodied properties:
public double Area => height * width;
If all you need is a variable to store some data:
public string Name { get; set; }
Want to make it appear read-only?
public string Name { get; private set; }
Or even better...
private readonly string _name;
...
public string Name { get { return _name; } }
Want to do some value checking before assigning the property?
public string Name
{
get { return m_name; }
set
{
if (value == null)
throw new ArgumentNullException("value");
m_name = value;
}
}
In general, the GetXyz() and SetXyz() are only used in certain cases, and you just have to use your gut on when it feels right. In general, I would say that I expect most get/set properties to not contain a lot of logic and have very few, if any, unexpected side effects. If reading a property value requires invoking a service or getting input from a user in order to build the object that I'm requesting, then I would wrap it into a method, and call it something like BuildXyz(), rather than GetXyz().
Use properties in C#, not get/set methods. They are there for your convenience and it is idiomatic.
As for your two C# examples, one is simply syntactic sugar for the other. Use the auto property if all you need is a simple wrapper around an instance variable, use the full version when you need to add logic in the getter and/or setter.
In C# favor properties for exposing private fields for get and/or set. The thie form you mention is an autoproperty where the get and set automatically generate a hidden pivot backing field for you.
I favor auto properties when possible but you should never do a set/get method pair in C#.
public string Name { get; set; }
This is simply a auto-implemented property, and is technically the same as a normal property. A backing field will be created when compiling.
All properties are eventually converted to functions, so the actual compiled implementation in the end is the same as you are used to in Java.
Use auto-implemented properties when you don't have to do specific operations on the backing field. Use a ordinary property otherwise. Use get and set functions when the operation has side effects or is computationally expensive, use properties otherwise.
Regardless of which way you choose in C# the end result is the same. You will get a backinng variable with separate getter and setter methods. By using properties you are following best practices and so it's a matter of how verbose you want to get.
Personally I would choose auto-properties, the last version: public string Name { get; set; }, since they take up the least amount of space. And you can always expand these in the future if you need add something like validation.
Whenever possible I prefer public string Name { get; set; } as it's terse and easily readable. However, there may be times when this one is necessary
private string name;
public string Name {
get { return name; }
set { name = value; }
}
In C# the preferred way is through properties rather than getX() and setX() methods. Also, note that C# does not require that properties have both a get and a set - you can have get-only properties and set-only properties.
public boolean MyProperty
{
get { return something; }
}
public boolean MyProperty
{
set { this.something = value; }
}
First let me try to explain what you wrote:
// private member -- not a property
private string name;
/// public method -- not a property
public void setName(string name) {
this.name = name;
}
/// public method -- not a property
public string getName() {
return this.name;
}
// yes it is property structure before .Net 3.0
private string name;
public string Name {
get { return name; }
set { name = value; }
}
This structure is also used nowadays but it is most suitable if you want to do some extra functionality, for instance when a value is set you can it to parse to capitalize it and save it in private member for alter internal use.
With .net framework 3.0
// this style is introduced, which is more common, and suppose to be best
public string Name { get; set; }
//You can more customize it
public string Name
{
get;
private set; // means value could be set internally, and accessed through out
}
Wish you better luck in C#
As mentioned, all of these approaches result in the same outcome. The most important thing is that you pick a convention and stick with it. I prefer using the last two property examples.
like most of the answers here, use Automatic properties. Intuitive, less lines of code and it is more clean. If you should serialize your class, mark the class [Serializable]/ with [DataConract] attribute. And if you are using [DataContract] mark the member with
[DataMember(Name="aMoreFriendlyName")]
public string Name { get; set; }
Private or public setter depends on your preference.
Also note that automatic properties require both getters and setters(public or private).
/*this is invalid*/
public string Name
{
get;
/* setter omitted to prove the point*/
}
Alternatively, if you only want get/set, create a backing field yourself
Which one should I use, and what are the caveats or subtleties involved with each approach?
When going with properties there is one caveat that has not been mentioned yet: With properties you cannot have any parametrization of your getters or setters.
For example imagine you want to retrieve a list items and want to also apply a filter at the same time. With a get-method you could write something like:
obj.getItems(filter);
In contrast, with a property you are forced to first return all items
obj.items
and then apply the filter in the next step or you have to add dedicated properties that expose items filtered by different criteria, which soon bloats your API:
obj.itemsFilteredByX
obj.itemsFilteredByY
What sometimes can be a nuisance is when you started with a property, e.g. obj.items and then later discovered that getter- or setter-parametrization is needed or would make things easier for the class-API user. You would now need to either rewrite your API and modify all those places in your code that access this property or find an alternative solution. In contrast, with a get-method, e.g. obj.getItems(), you can simply extend your method's signature to accept an optional "configuration" object e.g. obj.getItems(options) without having to rewrite all those places that call your method.
That being said, (auto-implemented) properties in C# are still very useful shortcuts (for the various reasons mentioned here) since most of the time parametrization may not be needed – but this caveat stands.
I've created this "question" as a community-wiki, because there is no right or wrong answer. I only would like to know how the community feels about this specific issue.
When you have a class with instance variables, and you also created properties that are simply getters and setters for these instance variables, should you use the properties inside your own class, or should you always use the instance variable?
Having auto-properties in C# 3.0 made this an even harder decision.
Using properties:
public class MyClass
{
private string _name;
// could be an auto-property of-course
public string Name { get { return _name; } set { _name = value; } }
public void Action()
{
string localVar = Name;
// ...
Name = "someValue";
// ...
}
}
Using instance variables:
public class MyClass
{
private string _name;
public string Name { get { return _name; } set { _name = value; } }
public void Action()
{
string localVar = _name;
// ...
_name = "someValue";
// ...
}
}
(for those who hate member prefixes, I apologize)
Personally, I always use the latter (instance variables), because I feel that properties should only be used by other classes, not yourself. That's why I mostly stay away from auto-properties as well.
Of course, things change when the property setter (or getter) does a little more than just wrapping the instance variable.
Are there compelling reasons to pick one or the other?
I always use instance variables as well. The reason is because properties might be doing stuff like validating arguments (like in a setter) for not null or not empty. If you're using the variable inside your class code, there's no need to go through the extra overhead of those checks (assuming you know the variable value is valid). The properties could be doing other things as well (logging, for example), that are important for the public API, but not for internal usage, so again, it's better to avoid the overhead and just use the instance variable in my opinion.
I think it becomes more difficult to change the internal implementation if the code uses its own public interface.
Difficult to explain but consider these expressions:
mTotalPrice = mPrice * mQuantity;
mTotalPrice = Price * Quantity;
What to do in the second expression if I need to change the internals to express all prices in € instead of $ (without affecting the public interface which still uses $)?
One solution is to make the expression more complex by adding the opposite of the change in the property.
mTotalPrice = Price / Rate * Quantity
The other solution is to start to use the private field instead.
mTotalPrice = mPrice * Quantity
In the end you get a mix of private and public use. The only way to get consistent use is to always use the private field.
I don't like prefixing members either, but actually I find I can write something like this accidently and not spot it until run time. Which kinda tempts me to avoid using properties where they're not necessary... but I still do, currently!
Public String MyString
{
{ get { return this.MyString; } } //<== Stack Overflow
{ set { this.myString = value; } }
}
private String myString;
I think that there is no difference between these two approaches.
Auto-implemented properties is just a quick way to access private members which are created any way.
Example from MSDN:
class Customer
{
// Auto-Impl Properties for trivial get and set
public double TotalPurchases { get; set; }
public string Name { get; set; }
public int CustomerID { get; set; }
// Constructor
public Customer(double purchases, string name, int ID)
{
TotalPurchases = purchases;
Name = name;
CustomerID = ID;
}
// Methods
public string GetContactInfo() {return "ContactInfo";}
public string GetTransactionHistory() {return "History";}
// .. Additional methods, events, etc.
}
99% of the time I use the property rather then the instance variable. In the past, I've worked with a lot of code that used the instance variable and when there was a bug associated with that variable, I had to put a breakpoint on every line of code that referenced it.
I decided to use properties instead, either public or private, to wrap around the instance variable. Doing this means that I only have to put a breakpoint in the getter/setter of the property if I need to debug an issue with the instance variable, rather then having (potentially) a lot of breakpoints scattered all over the code.