What is the difference (i.e. advantage/disadvantage) between the 2 properties that I created? Both seem to be correct, but what is the best way (practice) of declaring properties in a class?
[Serializable]
public class MySample
{
public string String1 = string.Empty;
private string _string2 = string.Empty;
public string String2
{
get { return _string2 ; }
set { _string2 = value; }
}
}
Only String2 is a property, the other is a public field.
See Difference between Property and Field in C# .NET 3.5+ for detail but if in doubt you should use properties rather than public fields.
If that seems like too much typing then you will be pleased to know that the following is equivalent
public string String2 { get; set; }
See auto-properties
Only String2 is a property. String1 is just a public field, and it is recommended to not declare public fields.
You can simplify the declaration of simple properties like this by using automatic properties:
public string String { get; set; }
The main difference between fields and properties is that fields are accessed directly, whereas properties are read and written to via get and set methods. When you declare an automatic property as above, these get and set methods are automatically generated for you by the compiler, as well as a backing field to store the actual value.
You can also execute additional code in the get and set methods, which is often used for things like change notification and validation. You can set the get and set methods to different visibilities, such as { get; private set; }, which is another thing that you don't have with fields.
Note that even if the usage of String1 and String2 in your example is the same, they are not binary compatible. That is, if you have a class that uses a field and you want to change that field to a property, you'll need to recompile all assemblies referencing that class. So it's best to go with (at least automatic) properties from the beginning.
The best way is to use auto-properties:
like this:
public string String1 {get;set;}
If you want a property from which you only read from, but not write to:
public string String1 {get; private set;}
If you want a property to which you only write to, but not read from:
public string String1 {set; private get;}
Generally it is recommended that you should not declare fields as public:
public string _string1; /*bad idea*/
The first this is that :
public string String1 = string.Empty;
is a field, not a property. You should generally avoid making public fields.
The second is a property with a field backer. This can be useful if you want to do some sort of validation before setting it. Or maybe have some sort of lazy initialisation before getting the value (obviously the lazy initialisation works better for more complex types or where the construction of the value, if not needed often, takes time).
The third option is an auto property, like this:
public string String3 { get; set; }
This compiles like a property, so if you change your code to be a field backed property to add extra functionality, then the signature of your class doesn't have to change and any existing code that uses the class won't need to be updated to call a property instead of a field (since it always was a property)
The first is not a property, but a field. The way you've implemented these here, there's effectively no difference, but in general, properties give you a lot more power.
See What is the difference between a Field and a Property in C#?
The usual way to implement a property in C# is:
public string String1 { get; set; }
Your String1 is actually a field, not a property. I suppose you were wanting an auto-implemented property, such as:
public string String1 { get; set; }
Your String2 is a field-backed property. One of the main differences between the two is that you have the opportunity to initialize the field-backed property by initializing the field instead of initializing the property in the constructor. Another important difference is that you have the opportunity in the field-backed property to do other things when the value is retrieved or set, such as performing change notification.
String1 is a public field, not a property. This is not recommended unless it's static readonly (and immutable!), like String.Empty.
Even if a field is fine now (though propably not state-of-the-art), changing it into a property later on breaks the binary compatibility of your class and thus is a breaking change.
Related
If the property can store data (as field does) why do we still need field?
For example i have this class,
public class Music
{
public Music() { }
public float musicBPM { get; set; }
public void addBPM()
{
this.muscBPM +=10;
}
}
Its still working like, as I have a private field and change its value, right?
So, whats the critical need of field if you can use the property?
Although automatic properties blur the distinction quite a bit, there is a fundamental difference between a field and a property:
A field is a data member capable of storing things,
A property is a method or a pair of methods which, through help of the compiler, can be used as if they were a field.
In other words, when you write
public float musicBPM { get; set; }
the compiler creates something like this:
private float musicBPM_property;
public float musicBPM {
get { return musicBPM_property; }
set { musicBPM_property = value; }
}
When you make an automatic property, the field is still there, but the compiler cleverly hides it from you.
That is why the fields are going to remain as a concept in .NET. However, automatic read-only properties of C# 6 make it possible to eliminate fields from the code that you write manually.
Property still needs a field as a backing repository, property actually consists of two methods (so called getter and setter) that access that backing field.
From msdn :
A property is a member that provides a flexible mechanism to read,
write, or compute the value of a private field. Properties can be used as if they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily and still helps promote the safety and flexibility of methods.
You don't assign values to your properties ... even though you do that end of the day gets assigned to a variable.
So when you say myprop = 20 the data actually getting assigned to a variable named somevar behind the scene.
public int myprop
{
set { somevar = value; }
}
If you are bit confused seeing auto properties and thinking that you are actually assigning the values to properties then that's not true. Behind the scene compiler will create private backing field to hold those values.
So, in a single sentence; properties gives you a way to encapsulate your class fields.
public int myprop {get; set; }
In C#, can you use a property without a field?
Edit for clarification:
private string _name;
public string Name
{
get { return _name; }
set { _name value; }
}
It seem's like they are always paired, is there a circumstance where we don't use the field at all?
All properties must have a field, assuming they are simple properties to store a value (*). However, the language (as of version 3.0) offers a way to declare the field implicitly. For example:
public int Value { get; set; }
That would declare a property named Value with an implicit field backing it and the getter and setter both public. You can include an accessibility keyword on either the getter or setter to restrict access to the property. For example:
public int Value { get; private set; }
In this case, only the owning type may call the setter, but any class can call the getter.
The next version of C# will have additional features for dealing with these "automatic properties", allowing you to provide a concise initialization syntax for them. For now, you have to initialize them in a constructor.
EDIT: based on your edited question, it seems worthwhile to address this specific question: "is there a circumstance where we don't use the field at all?"
The answer to that is, it's not common for no field to be involved at all. But it is possible, and it's not uncommon for a property to not use a field as storage for the property. For example, imagine a Rectangle object with an Area property:
class Rectangle
{
public double Width { get; private set; }
public double Height { get; private set; }
public double Area { get { return Width * Height; } }
}
Obviously there are fields involved (two of them), but there is not a field specifically dedicated to the Area property.
Another example would be where the property delegates. For example, in a WinForms Form subclass, it's common to expose specific control values via a property:
class MyForm : Form
{
public string EditText
{
get { return textBox1.Text; }
set { textBox1.Text = value; }
}
}
Again, the textBox1 field is being used here. But it actually represents something other than the property itself. The property is using a member of the object that field references.
I hope that clarifies the relationship between fields and properties adequately for you. Please feel free to ask for further clarifications if needed.
(*) Note that the only real rule for properties is that they have at least one of the getter or setter, and those methods can do whatever you want. I assume we are talking about simple value-based properties here.
A property is not required to have a field
public string Version
{
get
{
return "1.3.Awesome";
}
}
If you're asking what I think you are, the answer is yes, you just put get; set; inside the property declaration. C# encapsulates a variable for you.
EDIT: example
//no need for field declaration
public string Name
{
get;
set;
}
New to C#, and I understand that encapsulation is just a way of "protecting data". But I am still unclear. I thought that the point of get and set accessors were to add tests within those methods to check to see if parameters meet certain criteria, before allowing an external function to get and set anything, like this:
private string myName;
public string MyName;// this is a property, speical to c#, which sets the backing field.
private string myName = "mary";// the backing field.
public string MyName // this is a property, which sets/gets the backing field.
{
get
{
return myName;
}
set
{
if (value != "Silly Woman"){
myName = value;
}
}
}
But I've been seeing code in c# which just looks like this:
public string MyName { get; set; }
Why would you just have a get and set with nothing in there, - isn't that the same as just declaring your private backing field public? If you can just get and set it from outside, why wouldn't you just do it directly?
Indeed, creating an auto-property as follows:
public string Name { get; set; }
is identical to building a property backed by a field:
private string _name;
public string Name {
get { return _name; }
set { _name = value; }
}
The point of these properties is not to hide data. As you observed, they don't do this. Instead, these properties can do other stuff instead of just working with a field:
public string Name {
get { return _name; }
set { if (value == null) throw new Exception("GTFO!"); _name = value; }
}
Another thing is, you can make properties virtual:
public virtual string Name { get; set; }
which, if overridden, can provide different results and behaviours in a derived class.
By using public string MyName { get; set; }, you leave an ability to change its logic later without the need to recompile/change other code that uses your property.
For example, if you are making a library and v1 uses a field and v2 uses a property, applications that work with v1 will not work with v2 without recompilation (and, potentially, code changes if they are written in some .NET language that has different syntax for accessing fields).
Another important difference is in serialization scenarios -- a lot of them do not support fields. Also any interface that requires a property can not be implemented without using one, but depending on interface it may not be required to do any additional checks/logic in it.
It makes it easier to add logic later. If you have a class that has a public field that you want to change to a property, you have to recompile everything that uses your class. That's a key point that I didn't understand initially.
If you have a class:
public class MyClass
{
public string MyString;
}
You could access the value like this:
var myClass = new MyClass();
string s = myClass.MyString;
Now change that to a property:
public class MyClass
{
public string MyString { get; set; }
}
How is it accessed? The exact same way:
var myClass = new MyClass();
string s = myClass.MyString;
So no big deal, right? Well, actually....
Properties are actually compiled into getter and setter methods:
get_MyString() and set_MyString(string value)
So the two methods do produce different compiled code. Now if all your code that uses this class is in the same project, is not as big a deal, because it will all be compiled together. But if you have an API library that you've distributed, it can be a much bigger deal to update.
Because it is easier to change the Code if you want to add the checks/tests later on.
Especially if you have many inheritance and many classes in your code it is very hard to change the implementation from a public variable to a public Property.
Moreover you can add to the get and set within the property different attributes, e.g. if you are using reflection. The get and set of the property are internally different methods. If you have just a public variable /field it is not possible to added different properties to the different access ways.
Yeah, but you can easily change it to:
public string MyName { get; private set; }
Plus, properties are used in other scenarios, like DataContracts and Serialization... so, this is a nice feature... (Mostly, syntactic sugar. I think) EDIT: I take that back.. you can apply virtual to it, so it's not the same
This question already has answers here:
Public Fields versus Automatic Properties
(14 answers)
Closed 9 years ago.
Someone told me that you could replace the following code:
private string name;
public string Name
{
get;
set;
}
with the following and suffer no ill effects:
public string Name;
I realize that the property, set like in the first example does pretty much the same as it would if I removed it and set the original attribute to publicbut is it bad programming practice to go with the second way for attributes for which you need just the basic getter and setter?
The second way isn't a property, it's a field. The reason you should always use properties for public-facing values is that converting from a field to a property constitutes a breaking change. Using a property allows you to later change the behavior of the getter or setter without breaking any code that references yours.
Keep in mind, the code
public string Foo { get; set; }
is actually equivalent to
private string foo;
public string Foo
{
get { return foo; }
set { foo = value; }
}
When you use Properties you have better control of what properties have.
private string name;
public string Name
{
get;
set;
}
is wrong it should be either
public string Name
{
get;
set;
}
or
private string name;
public string Name
{
get { return name;}
set { this.name = value;}
}
sometimes when you want variable to be set only inside class u can use
public string Name
{
get;
private set;
}
Properties combine aspects of both fields and methods. To the user of an object, a property appears to be a field, accessing the property requires exactly the same syntax. To the implementer of a class, a property is one or two code blocks, representing a get accessor and/or a set accessor. The code block for the get accessor is executed when the property is read; the code block for the set accessor is executed when the property is assigned a new value. A property without a set accessor is considered read-only. A property without a get accessor is considered write-only. A property with both accessors is read-write.
Source: http://msdn.microsoft.com/en-us/library/w86s7x04(v=vs.80).aspx
I think the shortest way is to use Auto-Implemented Properties and some referenced information about them
In C# 3.0 and later, auto-implemented properties make property-declaration more concise when no additional logic is required in the property accessors. They also enable client code to create objects. When you declare a property as shown in the following example, the compiler creates a private, anonymous backing field that can only be accessed through the property's get and set accessors.
public string Name{ get; set;}
public string Name { get; set; }
msdn :
A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field. Properties can be used as if they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily and still helps promote the safety and flexibility of methods.
A public property isn't the same as a public instance variable.
And this difference can matter.
For instance, if you're using databound asp.net controls like DataTextField from DroDownListBox, it will fail if you set it to a instance variable instead of a public property.
The shortest way of writing a property is using automatic getters and setters.
This is not quite what you've put in your question though, you've replaced a traditional property that has a backing field, with a field.
An automatic getter/setter looks like this:
public string Blah { get; set; }
This feature was introduced in C# 3, I believe. So you have to target this, or above, in order to use these.
In C# do properties need to reference private member variables, or can I just declare the properties and use them directly in the class code?
If the former is the best practice, then does that rule out using C# property short-hand? I.e.
public string FirstName { get; set; }
Properties, when implemented like this:
public string FirstName { get; set; }
Automatically create a private member variable (the compiler does this for you), so you don't have to worry about it. This will behave exactly the same as if you do:
private string firstName;
public string FirstName {
get { return firstName; }
set { firstName = value; }
}
There is no reason not to use the automatic properties ( { get; set; } ). The provide the same advantages as making your own private member variable.
In addition, if you later decide you need to do extra processing (for example, if you decide to implement INotifyPropertyChanged in your property setter), you can add this without changing your public API, but putting a backing field in manually.
You don't need properties to access private fields but in general it is considered best practice.
And you can use auto-properties (short hand) untill you need to add more functionality to a property, like validation. Changing it to a 'real' property is always a non-breaking change.
Properties created like this
public String Caption{ get; set; }
this will be compiled as
[CompilerGenerated]
private string <Caption>k__BackingField;
public string Caption
{
[CompilerGenerated]
get
{
return this.<Caption>k__BackingField;
}
[CompilerGenerated]
set
{
this.<Caption>k__BackingField = value;
}
}
The above code is extracted after compilation using reflector tool.
They do not need to reference private member variables. You can use them directly in the class.
Properties do not need to reference private member variables. It is best practice, though, to have them do so. You can think of properties as methods if it makes it easier to understand. You can run code inside of them. You can return whatever you want. You can call methods and use private member variables. You can even simply return a constant.
I use private member variables in almost all cases. It allows me to create a readonly property, or to provide some rules to those outside my class of getting or setting properties that my class doesn't have to follow.
To add on to Reed's answer, inside of your code (within the class itself) the member functions should adhere to this and actually use the Property rather then the actual private member. For instance if you had this:
public string FirstName { get; set; }
And you had a strange method called public char GetFirstLetter() that returned the first letter in a person's first name you'd want to do it like this:
public char GetFirstLetter()
{
return FirstName[0];
}
Instead of actually using your private variable. When you set a property a programmer may have written code to set it in a particular manner. So it only makes sense to simply use that property within your class methods.
C# can reference private variables as in:
public class A
{
private string _b;
public string B
{
get { return _b; }
set { _b = value; }
}
}
The get;set; designation is automatic properties which when compiled will generate the private variable for you, as a way to make it easy to setup your code.
Using properties is the best way to provide a method of control and security to the attributes in a class, always keep the attributes private if possible.
if you use like
public string FirstName { get; set; }
compiler will automatically adds getters and setters for this property automatically.it not a bad practice.
Here is the proof
if you declare
private string firstName;
public string FirstName
{
get { return firstName; }
set { firstName = value; }
}
like this also compiler will takes it as
so its not ruled out... :)