I have many times written a C# property that looks like this:
private string _Id;
public string Id
{
get
{
return _Id;
}
set
{
_Id = value.Trim();
}
}
The above snippet declares a string property called Id and makes it so that the Trim extension method is automatically called on the value passed in to the setter. Without the Trim logic, I could have simply written:
public string Id {get; set;}
It seems like I've written a lot of code to accomplish something simple.
Is there a better way?
Is there a better way?
Well you can make it look like less code (and clutter things up less when reading it):
private string _Id;
public string Id
{
get { return _Id; }
set { _Id = value.Trim(); }
}
Or even put the whole property itself on a single line:
private string _Id;
public string Id { get { return _Id; } set { _Id = value.Trim(); } }
But no, you can't make an automatically implemented property do anything more than trivial get/set to a private variable.
To be honest, it's really not that much code - it's a fair amount of syntax but you've just had to declare a variable and write two statements. I don't think that's really too much to ask.
Related
This question already has answers here:
Any reason to use auto-implemented properties over manual implemented properties?
(7 answers)
Closed 5 years ago.
what is the different between writing the getter and setter directly like this:
public string Name {get; set;}
and like this:
private string _name;
public string Name
{
get
{
return this._name;
}
set
{
this._name = value;
}
}
I saw that in lots of codes. why they use a private member than a public getter and setter.
is it for performance or privacy or what is the point?
thank you.
what is the different between writing the getter and setter directly
like this
public string Name {get; set;}
They're essentially the same.
The code below you're basically creating the private field and providing both getters and setters for it, which of course does the intended idea. However, the language implementors decided they could make the life of a programmer easier by providing a shorter syntax where you can create a private field and at the same time provide a getter or setter or both.
private string _name;
public string Name
{
get
{
return this._name;
}
set
{
this._name = value;
}
}
So, in C# 3 they(language implementors) came up with the idea of making the syntax shorter by enabling a programmer to simultaneously create a private field and at the same time provide a getter or setter or both.
Behind the scenes, all that happens for the code below is the compiler creates a private field and also provides a getter and setter for it. So, basically, it's shorter more concise syntax to achieve the same task as the example above.
auto-implemented property
public string Name {get; set;}
There is none.
The thing is: auto-implemented properties weren't available until C# 3 (if you look at the documentation referenced: it goes back to VS 2008 which was released with C# 3), and not all code was written in the C# 3 era. Also, not all developers are aware of this feature. If I would stumble across this kind of code, I would rewrite it to use auto-implemented properties.
An property is just a short hand and will create at the background an public get method and a public set method and a private field to store the value.
Example Code
// example property
public string Name { get; set; }
// at run time it is the same as:
private string Name;
public string GetName(){
return this.Name;
}
public string SetName(string name){
this.Name = name;
}
See Image :
The sample class only has an property in code Name.
If you use Reflection to get all the members off the Sample class you will see that at run time set_name() and get_name() methods are generated.
These methods are not specified in in code.
Short answer, there isn't a difference. The compiler will convert the "auto" property to that style regardless, it's just saving you the writer a few keystrokes. It really only comes into play when you start working with DataBinding or having to do something else in the Set portion.
private string _name;
public string Name
{
get
{
return this._name;
}
set
{
this._name = value;OnPropertyChange();
}
}
In WPF/XAML/DataBinding, this would let anyone subscribed to this object know that a property with the name "Name" has changed and it should reflect so in the UI.
The first one is called an auto-implemented property.
Second one is used when you want to add some custom code logic that validates the value in your setter.
You can control what happens in the getter & setters, whereas if the member was public, the variable could be modified directly.
private string _name;
public string Name
{
get
{
return this._name + " likes chocolate";
}
set
{
this._name = value;
}
}
Here, your private _name always stays the same, but anyone accessing Name will get _name + " likes chocolate".
In the setter, you could do some validation.
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
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
Is there any difference between the two pieces of code below? Or is the top just a short form of the bottom one?
public string Name { get; set; }
and
private string _Name;
public string Name
{
get { return _Name; }
set { _Name = value; }
}
The only difference (other than the fact you would have to do the initialization with "Default Name" in your class constructor) is that _Name will be visible within the class itself. There's a risk that the class will internally reference _Name rather than Name, everything will work fine, and at some later point in time you'll add some logic to Name that will not be called because you're using _Name within the class.
Example:
private string _Name = "Default Name";
public string Name
{
get { return _Name.Left(42); } // Changed the getter
set { _Name = value; }
}
void MyOtherMethod()
{
string foo = _Name; // Referencing the private field accidentally instead of the public property.
// Do something with foo
}
Basic behavior and purpose of both of the property method is almost same. But the major difference is in the implementation. The difference between
public string Name{get;set;}
AND
private string _Name;
public string Name
{
get { return _Name; }
set { _Name=value; }
}
is if you use short property syntax (introduced in framework 3.0 or later), then the property sting is never initialized i.e. if you directly use "Name" property anywhere without setting the value to it, it will return a NULL value. But if you use second syntax to initialize the property value, it will return a EMPTY string because when you initialize a string, it is initialized with a EMPTY value not the NULL. So if you return the property value without initializing using FULL Property Method, it will always return the EMPTY string not the NULL value.
I dont think there is any difference in compiled code. The reason why you may want to do the full way though is if you want to add a default value (which can be done in the constructor in short hand form), or add additional code to the getter or setter
EDIT: Actually, your code is wrong it should be
private string _Name;
public string Name
{
get { return _Name; }
set { _Name = value; }//change here
}
not...
value = _Name;
One difference is that you can set a default on the private string when you do this
private string _Name = "Default Name";
public string Name
{
get { return _Name; }
set { value = _Name; }
}
Once compiled the two examples you showed are the same.
It is simply a short form, the underlying variable is still generated as a supporting backing field (where the data is stored,) but automatically - this is useful if you are literally just getting and setting and don't need any specific implementation details in either accessor.
For this particular implementation of second form, both are equivalent. Because the compiler will generate almost the same code if you simply write the first form.
That is, the compiler is going to add code to it:
public string Name{get;set;}
making it look like this:
private string generatedCode_Name;
public string Name
{
get { return generatedCode_Name; }
set { generatedCode_Name = value; }
}
By the way, this is incorrect
set { value = _Name; } //I believe its a typo!
I think you meant:
set { _Name = value; }
For the example as written they are an exact equivalent.
Auto-implemented properties are syntactic sugar introduced to address exactly these type of situation, where the property is used just to avoid having a public field, with no extra logic in the getter/setter. However, an auto-implemented property gives you all the benefits of properties, including metadata. Here's a rather old but still relevant link that explains a little bit more about them.
Behind the scenes, the compiler generates a backing field very similar to your own.
The point of const-correctness is to be able to provide a view of an instance that can't be altered or deleted by the user. The compiler supports this by pointing out when you break constness from within a const function, or try to use a non-const function of a const object. So without copying the const approach, is there a methodology I can use in C# that has the same ends?
I'm aware of immutability, but that doesn't really carry over to container objects to name but one example.
I've come across this issue a lot of times too and ended up using interfaces.
I think it's important to drop the idea that C# is any form, or even an evolution of C++. They're two different languages that share almost the same syntax.
I usually express 'const correctness' in C# by defining a read-only view of a class:
public interface IReadOnlyCustomer
{
String Name { get; }
int Age { get; }
}
public class Customer : IReadOnlyCustomer
{
private string m_name;
private int m_age;
public string Name
{
get { return m_name; }
set { m_name = value; }
}
public int Age
{
get { return m_age; }
set { m_age = value; }
}
}
To get the benefit of const-craziness (or pureness in functional programming terms), you will need to design your classes in a way so they are immutable, just like the String class of c# is.
This approach is way better than just marking an object as readonly, since with immutable classes you can pass data around easily in multi-tasking environments.
I just wanted to note for you that many of the System.Collections.Generics containers have an AsReadOnly method which will give you back an immutable collection.
C# doesn't have such feature. You can pass argument by value or by reference. Reference itself is immutable unless you specify ref modifier. But referenced data isn't immutable. So you need to be careful if you want to avoid side effects.
MSDN:
Passing Parameters
Interfaces are the answer, and are actually more powerful than "const" in C++. const is a one-size-fits-all solution to the problem where "const" is defined as "doesn't set members or call something that sets members". That's a good shorthand for const-ness in many scenarios, but not all of them. For example, consider a function that calculates a value based on some members but also caches the results. In C++, that's considered non-const, although from the user's perspective it is essentially const.
Interfaces give you more flexibility in defining the specific subset of capabilities you want to provide from your class. Want const-ness? Just provide an interface with no mutating methods. Want to allow setting some things but not others? Provide an interface with just those methods.
Agree with some of the others look at using readonly fields that you initialize in the constructor, to create immutable objects.
public class Customer
{
private readonly string m_name;
private readonly int m_age;
public Customer(string name, int age)
{
m_name = name;
m_age = age;
}
public string Name
{
get { return m_name; }
}
public int Age
{
get { return m_age; }
}
}
Alternatively you could also add access scope on the properties, i.e. public get and protected set?
public class Customer
{
private string m_name;
private int m_age;
protected Customer()
{}
public Customer(string name, int age)
{
m_name = name;
m_age = age;
}
public string Name
{
get { return m_name; }
protected set { m_name = value; }
}
public int Age
{
get { return m_age; }
protected set { m_age = value; }
}
}
The const keyword can be used for compile time constants such as primitive types and strings
The readonly keyword can be used for run-time constants such as reference types
The problem with readonly is that it only allows the reference (pointer) to be constant. The thing referenced (pointed to) can still be modified. This is the tricky part but there is no way around it. To implement constant objects means making them not expose any mutable methods or properties but this is awkward.
See also Effective C#: 50 Specific Ways to Improve Your C# (Item 2 - Prefer readonly to const.)