什么是{得到; 放; C# 中的语法？

Question

I am learning ASP.NET MVC and I can read English documents, but I don't really understand what is happening in this code:

public class Genre
{
    public string Name { get; set; }
}

What does this mean: { get; set; } { get; set; } { get; set; } ?

Answer 1

It's a so-called auto property, and is essentially a shorthand for the following (similar code will be generated by the compiler):

private string name;
public string Name
{
    get
    {
        return this.name;
    }
    set
    {
        this.name = value;
    }
}

Answer 2

So as I understand it { get; set; } { get; set; } { get; set; } is an "auto property" which just like @Klaus and @Brandon said is shorthand for writing a property with a "backing field." So in this case:

public class Genre
{
    private string name; // This is the backing field
    public string Name   // This is your property
    {
        get => name;
        set => name = value;
    }
}

However if you're like me - about an hour or so ago - you don't really understand what properties and accessors are, and you don't have the best understanding of some basic terminologies either. MSDN is a great tool for learning stuff like this but it's not always easy to understand for beginners. So I'm gonna try to explain this more in-depth here.

get and set are accessors , meaning they're able to access data and info in private fields (usually from a backing field ) and usually do so from public properties (as you can see in the above example).

There's no denying that the above statement is pretty confusing, so let's go into some examples. Let's say this code is referring to genres of music. So within the class Genre, we're going to want different genres of music. Let's say we want to have 3 genres: Hip Hop, Rock, and Country. To do this we would use the name of the Class to create new instances of that class.

Genre g1 = new Genre(); //Here we're creating a new instance of the class "Genre"
                        //called g1. We'll create as many as we need (3)
Genre g2 = new Genre();
Genre g3 = new Genre();

//Note the () following new Genre. I believe that's essential since we're creating a
//new instance of a class (Like I said, I'm a beginner so I can't tell you exactly why
//it's there but I do know it's essential)

Now that we've created the instances of the Genre class we can set the genre names using the 'Name' property that was set way up above.

public string Name //Again, this is the 'Name' property
{ get; set; } //And this is the shorthand version the process we're doing right now 

We can set the name of 'g1' to Hip Hop by writing the following

g1.Name = "Hip Hop";

What's happening here is sort of complex. Like I said before, get and set access information from private fields that you otherwise wouldn't be able to access. get can only read information from that private field and return it. set can only write information in that private field. But by having a property with both get and set we're able do both of those functions. And by writing g1.Name = "Hip Hop"; we are specifically using the set function from our Name property

set uses an implicit variable called value . Basically what this means is any time you see "value" within set , it's referring to a variable; the "value" variable. When we write g1.Name = we're using the = to pass in the value variable which in this case is "Hip Hop" . So you can essentially think of it like this:

public class g1 //We've created an instance of the Genre Class called "g1"
{
    private string name;
    public string Name
    {
        get => name;
        set => name = "Hip Hop"; //instead of 'value', "Hip Hop" is written because 
                              //'value' in 'g1' was set to "Hip Hop" by previously
                              //writing 'g1.Name = "Hip Hop"'
    }
}

It's Important to note that the above example isn't actually written in the code. It's more of a hypothetical code that represents what's going on in the background.

So now that we've set the Name of the g1 instance of Genre , I believe we can get the name by writing

console.WriteLine (g1.Name); //This uses the 'get' function from our 'Name' Property 
                             //and returns the field 'name' which we just set to
                             //"Hip Hop"

and if we ran this we would get "Hip Hop" in our console.

So for the purpose of this explanation I'll complete the example with outputs as well

using System;
public class Genre
{
    public string Name { get; set; }
}

public class MainClass
{
    public static void Main()
    {
        Genre g1 = new Genre();
        Genre g2 = new Genre();
        Genre g3 = new Genre();

        g1.Name = "Hip Hop";
        g2.Name = "Rock";
        g3.Name = "Country";

        Console.WriteLine ("Genres: {0}, {1}, {2}", g1.Name, g2.Name, g3.Name);
    }
}

Output:

"Genres: Hip Hop, Rock, Country"

Answer 3

Those are automatic properties

Basically another way of writing a property with a backing field.

public class Genre
{
    private string _name;

    public string Name 
    { 
      get => _name;
      set => _name = value;
    }
}

Answer 4

This is the short way of doing this:

public class Genre
{
    private string _name;

    public string Name
    {
      get => _name;
      set => _name = value;
    }
}

Answer 5

It is a shortcut to expose data members as public so that you don't need to explicitly create a private data members. C# will creates a private data member for you.

You could just make your data members public without using this shortcut but then if you decided to change the implementation of the data member to have some logic then you would need to break the interface. So in short it is a shortcut to create more flexible code.

Answer 6

Basically, it's a shortcut of:

class Genre{
    private string genre;
    public string getGenre() {
        return this.genre;
    }
    public void setGenre(string theGenre) {
        this.genre = theGenre;
    }
}
//In Main method
genre g1 = new Genre();
g1.setGenre("Female");
g1.getGenre(); //Female

Answer 7

它是 C# 的自动实现属性。

Answer 8

• The get/set pattern provides a structure that allows logic to be added during the setting ('set') or retrieval ('get') of a property instance of an instantiated class, which can be useful when some instantiation logic is required for the property.

• A property can have a 'get' accessor only, which is done in order to make that property read-only

• When implementing a get/set pattern, an intermediate variable is used as a container into which a value can be placed and a value extracted. The intermediate variable is usually prefixed with an underscore. this intermediate variable is private in order to ensure that it can only be accessed via its get/set calls. See the answer from Brandon, as his answer demonstrates the most commonly used syntax conventions for implementing get/set.

Answer 9

They are the accessors for the public property Name.

You would use them to get/set the value of that property in an instance of Genre.

Answer 10

That is an Auto-Implemented Property. It's basically a shorthand way of creating properties for a class in C#, without having to define private variables for them. They are normally used when no extra logic is required when getting or setting the value of a variable.

You can read more on MSDN's Auto-Implemented Properties Programming Guide .

Answer 11

In the Visual Studio, if you define a property X in a class and you want to use this class only as a type, after building your project you will get a warning that says "Field X is never assigned to, and will always has its default value" .

By adding a { get; set; } { get; set; } { get; set; } to X property, you will not get this warning.

In addition in Visual Studio 2013 and upper versions, by adding { get; set; } { get; set; } { get; set; } you are able to see all references to that property.

Answer 12

This mean that if you create a variable of type Genre, you will be able to access the variable as a property

Genre oG = new Genre();
oG.Name = "Test";

Answer 13

Such { get; set; } { get; set; } { get; set; } syntax is called automatic properties, C# 3.0 syntax

You must use Visual C# 2008 / csc v3.5 or above to compile. But you can compile output that targets as low as .NET Framework 2.0 (no runtime or classes required to support this feature).

Answer 14

Its basically a shorthand. You can write public string Name { get; set; } public string Name { get; set; } public string Name { get; set; } like in many examples, but you can also write it:

private string _name;

public string Name
{
    get { return _name; }
    set { _name = value ; } // value is a special keyword here
}

Why it is used? It can be used to filter access to a property, for example you don't want names to include numbers.

Let me give you an example:

private class Person {
    private int _age;  // Person._age = 25; will throw an error
    public int Age{
        get { return _age; }  // example: Console.WriteLine(Person.Age);
        set { 
            if ( value >= 0) {
                _age = value; }  // valid example: Person.Age = 25;
        }
    }
}

Officially its called Auto-Implemented Properties and its good habit to read the ( programming guide ). I would also recommend tutorial video C# Properties: Why use "get" and "set" .

Answer 15

Get set are access modifiers to property. Get reads the property field. Set sets the property value. Get is like Read-only access. Set is like Write-only access. To use the property as read write both get and set must be used.

Answer 16

Get is invoked when the property appears on the right-hand side (RHS) Set is invoked when the property appears on the left-hand side (LHS) of '=' symbol

For an auto-implemented property, the backing field works behind the scene and not visible.

Example:

public string Log { get; set; }

Whereas for a non auto-implemented property the backing field is upfront, visible as a private scoped variable.

Example:

private string log;

public string Log
{
    get => log;
    set => log = value;
}

Also, it is worth noted here is the 'getter' and 'setter' can use the different 'backing field'

Answer 17

A property is a like a layer that separates the private variable from other members of a class. From outside world it feels like a property is just a field, a property can be accessed using .Property

public class Person
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string FullName => $"{FirstName} {LastName}";
}

public class Person
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string FullName { get { return $"{FirstName} {LastName}"; } }
}

FullName is a Property. The one with arrow is a shortcut. From outside world, we can access FullName like this:

var person = new Person();
Console.WriteLine(person.FullName);

Callers do not care about how you implemented the FullName. But inside the class you can change FullName whatever you want.

Check out Microsoft Documentation for more detailed explanation:

https://docs.microsoft.com/en-us/dotnet/csharp/properties

Answer 18

Basically it helps to protect your data. Consider this example without setters and getter and the same one with them.

Without setters and getters

Class Student

using System;
using System.Collections.Generic;
using System.Text;

namespace MyFirstProject
{
    class Student
    {
        public string name;
        public string gender;
        public Student(string cName, string cGender)
        {
            name = cName;
            gender= cGender;
        }

     }
}

In Main

 Student s = new Student("Some name", "Superman"); //Gender is superman, It works but it is meaningless
 Console.WriteLine(s.Gender);

With setters and getters

using System;
using System.Collections.Generic;
using System.Text;

namespace MyFirstProject
{
    class Student
    {
        public string name;
        private string gender;
        public Student(string cName, string cGender)
        {
            name = cName;
            Gender = cGender;
        }

        public string Gender
        {
            get { return gender; }
            set
            {
                if (value == "Male" || value == "Female" || value == "Other")
                {
                    gender = value;
                }
                else
                {
                    throw new ArgumentException("Invalid value supplied");
                }
            }
        }
    }
}

In Main:

  Student s = new Student("somename", "Other"); // Here you can set only those three values otherwise it throws ArgumentException.
Console.WriteLine(s.Gender);

Answer 19

Define the Private variables

Inside the Constructor and load the data

I have created Constant and load the data from constant to Selected List class.

public  class GridModel
{
    private IEnumerable<SelectList> selectList;
    private IEnumerable<SelectList> Roles;

    public GridModel()
    {
        selectList = from PageSizes e in Enum.GetValues(typeof(PageSizes))
                       select( new SelectList()
                       {
                           Id = (int)e,
                           Name = e.ToString()
                       });

        Roles= from Userroles e in Enum.GetValues(typeof(Userroles))
               select (new SelectList()
               {
                   Id = (int)e,
                   Name = e.ToString()
               });
    }

  public IEnumerable<SelectList> Pagesizelist { get { return this.selectList; } set { this.selectList = value; } } 
  public IEnumerable<SelectList> RoleList { get { return this.Roles; } set { this.Roles = value; } }
  public IEnumerable<SelectList> StatusList { get; set; }

}