In both Ruby and PHP (and I guess other languages as well) there are some utility methods that are called whenever a property is set. ( *instance_variable_set* for Ruby, *__set* for PHP).
So, let's say I have a C# class like this:
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
Now, let's say that if any property setter from the Person class is called, I want to call another method first, and then continue with the default behaviour of the setter, and the same applies for the property setters.
Is this possible?
Edit:
I want to do this without defining a backing field.
Not generally; a few options though;
inherit from ContextBoundObject - which does allow this, but at a performance cost
write an explicit property (i.e. with a backing field), and add a utility method call manually
look at compile-time weavers, such as PostSharp - generally by spotting an attribute or similar
look at runtime code generators, as offered by some DI/IoC tools (and some other "decorator" based tools) - which either decorate or subclass your object to add the extra code
It is possible to do directly in the property body itself, but then you need to use a proper backing field instead of auto-implemented properties.
private string firstName;
public string FirstName
{
get { return firstName;}
set
{
if(check(value))
{
firstName = value;
}
}
}
Even with auto-implemented properties you get a backing field - this is generated by the compiler and you don't have direct access to it.
Edit:
Seeing as you don't want a backing field, you have other options - using an AOP tool such as PostSharp could help with that.
You will have to write the properties in full to achieve this.
I know this has been properly answered but I'll include an example to show you the syntax to achieve what you want:
public class Person
{
private
public string FirstName
{
get
{
return _firstName;
}
set
{
// see how we can call a method below? or any code for that matter..
_firstName = SanitizeName(value);
}
}
}
Are you in a position to rewrite your class to implement an interface? If so, Unity's interface interceptor might give you what you need. If an interface is not an option then that link also documents Unity's type and instance interceptors.
Not out of the box. You would need to insert code into each properties setter and getter, either manually or automatically using IL rewriting.
When you want to do it manually, you can't use automatic properties any more.
When you want to do it automatically, have a look at AOP.
Yes, of course...
In your example you are using automatic properties, without a backing field.... You just need to create a backing field for your property, and then you can do what you want in the setter and getter.
example:
private string firstName;
public string FirstName
{
get { return firstName; }
set { doMethod(); firstName = value;}
}
Mocking frameworks can do this, as well as IoC libraries like Unity. The only other way to do such a thing would be to use IL-rewriting (as previously mentioned).
You cant use automatic properties. You would have to dinfe the property out the old fashion way with a backing field and call the method manually.
public class Person
{
private string _FirstName;
public string FirstName
{
get
{
return _FirstName;
}
set
{
SomeMethod();
_FirstName = value;
}
}
private void SomeMethod()
{
//do something
}
}
As far as I know, you have to use a backing field and put the call to the other method inside the setter thusly:
public class Person {
private string firstName;
private string lastName;
public string FirstName {
set {
DoSomeStuff();
firstName = value;
}
get { return firstName; }
}
public string LastName {
set {
DoSomeStuff();
lastName = value;
}
get { return lastName; }
}
}
Related
Usually I would build my field like this:
private string name;
public void setName(string name){
this.name = name;
}
public string getName(){
return name
}
that works perfectly when doing this: string myString = object.getName() or object.setName("Alex").
However, I thought I might give the inbuilt C# functions a try.
So I did this:
private string name { get; set; }
however, that won't work at all. When I try to access the field with object.name, I can't even access it due to private restriction.
Did I misunderstand something about these predefined get/sets?
If I had to mark every field as public, why should I even use getters or setters? I could access the field like in the snippet above without get and set?
You're mixing up way too many things - you might want to read a book on C#, really. It usually takes some time to get rid of some of the preconceptions from your old programming language - but you really do want to do that; even Java and C# are incredibly different when you go beyond the surface appearance.
First, nothing is forcing you to use auto-properties. If you want to use properties while keeping your manual backing fields, you can simply use this:
private string name;
public string Name { get { return name; } set { name = value; } }
If you do want to use auto-properties, you have to understand that the backing field is hidden - you're only declaring the property; and you want that property to be public (though you can also use accessibility modifiers on the individual get/set "methods", e.g. private set). But the field is never accessible - it's "always" behind the property.
To mirror your original code, this is what you want:
public string Name { get; set; }
Only if you ever need to move away from using auto-properties (that is, you need to add some logic to either the getter or the setter), you will have to reintroduce the manual backing field, and stop using auto-properties - see the first code sample in my answer.
Did I misunderstand something about these predefined get/sets?
Yes, you did. The property itself has to be public. If you're using auto-properties, then you can't do any validation since the backing field is compiler generated. If you want to actually do something with the value before, you can use a property with a backing field:
private string name;
public string Name
{
get { return name; }
set
{
if (string.IsNullOrEmpty(name))
throw new ArgumentException("name cannot be null");
name = value
}
}
Because this:
public string Name { get; set; }
Generated a backing field like this:
[DebuggerBrowsable(DebuggerBrowsableState.Never), CompilerGenerated]
private string <Name>k__BackingField;
public string Name
{
[CompilerGenerated]
get
{
return this.<Name>k__BackingField;
}
[CompilerGenerated]
set
{
this.<Name>k__BackingField = value;
}
}
Just do
public string Name { get; set; }
That compiles down to a private field with an unspeakable name, and a public property. That public property has a public get method and a public set method.
Seems to be exactly what you want.
Alternatively, use
public string Name { get; private set; }
Your get method will be public as before, but the set method will be private then.
As of C# 6 (Visual Studio 2015), you can even do
public string Name { get; }
In that case, there is no set method, not even a private one, but you can assign to the underlying field through the property in the constructor.
Did I misunderstand something about these predefined get/sets?
Yes, a bit.
If I had to mark every field as public, why should I even use getters or setters? I could access the field like in the snippet above without get and set?
This is the part that you're missing. The syntax you are talking about it called an auto-implemented property. That is, when you write:
public string Name { get; set; }
the C# compiler generates a private field, getter, and setter behind the scenes for you. You can see them if you look at the metadata for your class, and get access to them via reflection. They have the exact same names as the getter or setter you would write yourself (typically get_Name and set_Name). The only difference is, you didn't have to write them.
The reason to do this is because most getter/setter pairs only exist to add a layer of abstraction over a private field, and consist of a single return name or name = value line of code. If that's all you want, you may as well let the compiler write it for you.
However, if you ever needed something more complex, you can manually implement the getter and setter yourself, and callers won't know the difference. In other words, if you change:
public string Name { get; set; }
to
private string name;
public string Name
{
get
{
return name;
}
set
{
name = value;
RecalculateSomeStuff();
}
}
then the metadata for your class is identical. Anyone using your class does not have to even be recompiled to pick up the new setter, because as far as the callers are concerned, they're still called set_Name directly.
What the others want to tell you is that you should deferentiate between fields (privates) and properties (public) (is not a rule but a convention)
private string name;
public string Name{ get; set;}
// you can acces to the property:
var objectName = YourObject.Name
// and set the value of your property:
YourObject.Name = "whatever"
First of all the equivalent of your code is
private string _name;
public string Name
{
get {return _name;}
set { _name = value; }
}
OR simply
public string Name { get; set; }
To define the accessibility level of the "Name" field, you put the access modifiers (public, protected, etc.) before get or set
Example
//Read only properties
public string Name
{
get {return _name;}
private set { _name = value; }
}
To have more details and see difference between public fieal and public property see Difference between Auto - Implemented Properties and normal public member
PS :
To write this in Visual studio you can use snippet, type prop keyword then tab key or propfull and press tab key. press tab key our shift+tab to navigate between highlighted fields
This question already has answers here:
OO Design - do you use public properties or private fields internally? [duplicate]
(10 answers)
Closed 9 years ago.
class Student
{
private string firstName;
public string FirstName
{
get
{
return firstName;
}
set
{
firstName = value; // Possible logical checks may be implemented here in the future
}
}
public Student (firstName)
{
this.firstName = firstName; // Option 1
// Or
FirstName = firstName; // Option 2
}
}
which of the two lines is more standard?
do we use the private or the public members in the constructor?
You could go with option 3
public string FirstName {get; set;}
public Student (firstName)
{
FirstName = firstName;
}
It depends... Often on things not included in your example. For one thing, your entire property can be shortened to an auto-implemented property:
public string FirstName { get; set; }
Which would make the question moot in this case. Beyond that, the question comes down to what sort of logic may exist (now or in the future) in the property and whether or not that logic needs to be invoked by the constructor.
For example, does the property internally check for a required value or perform some other validation? Something like this:
private string firstName;
public string FirstName
{
get { return firstName; }
set
{
if (string.IsNullOrWhiteSpace(value))
throw new ArgumentNullException("FirstName");
firstName = value;
}
}
In a case like this clearly you'd want the constructor to use the property and not the backing field so that the logic is applied when constructing the object.
Conversely, you might have logic that should only be used when accessing the setter but not when constructing the object. Off the top of my head one example might be an object which maintains information about a Location. It might have an Address property and a Coordinates property, and any time one of them changes there is a back-end process to geolocate the new value and update the other. But you might have a constructor which accepts both (perhaps when re-building an existing Location from a database) and it wouldn't make sense to perform the geolocation during construction. In that case you'd set the backing fields and not the properties.
For lack of a compelling reason not to use the properties, I'd generally prefer to use them instead of the backing fields. Simply because logic might be added to those properties later that all accessors should use. I also find it more likely that the properties have a more meaningful name than backing fields (for example, FirstName is more readable/meaningful than _firstName) so the preference would be to keep the rest of the code as readable as possible and to prefer more readable names.
It is a stylistic choice that doesn't really matter. Personally, I use the public property name, because I like to use auto properties, and that is the only option in that case. Using the public property keeps my code consistent.
When I am writing POCOs (Plain Old CLR Objects) where things are trivial, I go with this approach:
public class POCO
{
public POCO()
{
Name = "Moo-Juice";
}
public string Name { get; set; }
}
In non-trivial cases where I actually need the member variable, I prefix it with _ (this helps in intellisense, believe me - and allows you to distinguish between members and locals):
public class NonTrivial
{
private string _name;
public NonTrivial()
{
_name = "Jon Skeet"; // He is non-trivial
}
}
This way I avoid polluting my code with this. everywhere.
It depends:
private string firstName;
public string FirstName
{
get
{
return firstName;
}
set
{
firstName = (value=="mycheck")?"default":value;
}
}
If your property has some validations then you should go for:
public Student (firstName)
{
FirstName = firstName;
}
The most common is to use the property, but it is a matter of choice.
In this case particularly, you should use automatic property:
public string FirstName { get; set; }
And the compiler adds the backing field automatically.
You can also choose to not add the parameter constructor, as since C# 3.5 (IIRC), you can use automatic initializers:
new Studant() { FirstName = "John Doe" }
Which calls the constructor, and sets the property in one line.
Overall, I tend to only request a constructor parameter for things it really depend on (see: dependency injection), and let the not always needed ones optional until they are required, like validating before persisting.
I'm going to build my MVC Web Application and I created my data models.
I found online many ways to compile a data model code. This is easiest one, using only public properties:
public class Person
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
But I also found a version using a private variable and a public properies, like this:
public class Person
{
private int id;
private string firstName;
private string lastName;
public int Id { get { return id; } set { id = value; } }
public string FirstName { get { return firstName; } set { firstName = value; } }
public string LastName { get { return lastName; } set { lastName = value; } }
}
What is the difference between these two data models?
When is more advisable using the first one or the second one?
This is the same like asking: what is a difference bwteen auto properties and normal properties.
Auto properties:
easy creation (less to type)
internal field is generated for you automatically by compiler
Not possible to debug (set a break point inside the property)
Normal properties
Sligtly more code to type
Easy to debug
More code can be injected inside get and set
If first example compiler will create private field for every automatic property itself, but they behave exactly the same. More info on MSDN
I would suggest second approach as you have more control how property works, but there is nothing wrong in using first one.
The fiest block you have are auto-properties, and under the hood the c# will be compiled similar to the second block, so in this case there is no difference. Take a look at these posts here:
C# 3.0 auto-properties - useful or not?
What are Automatic Properties in C# and what is their purpose?
Any reason to use auto-implemented properties over manual implemented properties?
If you were implementing the INotifyPropertyChanged interface, then you would need to use the traditional way as you would be interacting with the property in the setter, see example...
http://msdn.microsoft.com/en-us/library/ms743695.aspx
I'm a newbie and I'm trying to learn the basics of C#. This might sound quite trivial and may be stupid but its a doubt. While going through one of the source codes of an application, I saw a piece of code inside a class
private string fname;
public string FirstName
{
get
{
return fname
}
set
{
fname = value;
}
}
Can anyone tell me what it means. I understand that when we declare a class we access fname using an alias FirstName. If it's for some security purpose then what?
This code is also equivalent to:
public string FirstName { get; set; }
What this do is define a property. In C# properties provide encapsulation for private fields.
You can write your custom logic on your property. F.e, some validation:
public string FirstName
{
get
{
return fname;
}
set
{
if (value.Count(s => Char.IsDigit(s)) > 0)
{
throw new Exception("Only letters allowed");
}
fname = value;
}
}
fname is a field and has private visibility but FirstName is a public property therefore it will be visible outside of the class and can contain logic inside get and set methods
It's called Properties (MSDN article). The reason for using them is to encapsulate accessing some class field to be able to easily change class behavior in future if needed.
This is also equivalent to so called auto-property, since the property at this moment oftimedoes not add any logic:
public string FirstName { get; set; }
get and set methods are called accessors(getters) and mutators(setters) these methods are used to access and mutate the attributes of an object without allowing the access from outside the class.
See that access modifier of the variable fname is private which means it can only be accessed by any method inside the class.
and note that the get and set methods should normally be given the public access modifier which enables the method to be accessed from any outside class.
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... :)