C＃获取/设置语法用法

Question

These are declarations for a Person class.

protected int ID { get; set; }
protected string Title { get; set; }
protected string Description { get; set; }
protected TimeSpan jobLength { get; set; }

How do I go about using the get/set? In main, I instantiate a

Person Tom = new Person();

How does Tom.set/get??

I am use to doing C++ style where you just write out the int getAge() and void setAge() functions. But in C# there are shortcuts handling get and set?

Answer 1

Assuming you have access to them (the properties you've declared are protected ), you use them like this:

Person tom = new Person();
tom.Title = "A title";
string hisTitle = tom.Title;

These are properties . They're basically pairs of getter/setter methods (although you can have just a getter, or just a setter) with appropriate metadata. The example you've given is of automatically implemented properties where the compiler is adding a backing field. You can write the code yourself though. For example, the Title property you've declared is like this:

private string title; // Backing field
protected string Title
{
    get { return title; }  // Getter
    set { title = value; } // Setter
}

... except that the backing field is given an "unspeakable name" - one you can't refer to in your C# code. You're forced to go through the property itself.

You can make one part of a property more restricted than another. For example, this is quite common:

private string foo;
public string Foo
{
    get { return foo; }
    private set { foo = value; }
}

or as an automatically implemented property:

public string Foo { get; private set; }

Here the "getter" is public but the "setter" is private.

Answer 2

Assuming you have a song class (you can refer below), the traditional implementation would be like as follows

 class Song
  {
       private String author_name;
       public String setauthorname(String X) {}; //implementation goes here
       public String getauthorname() {}; //implementation goes here
  }

Now, consider this class implementation.

      class Song 
      {
            private String author_name;
            public String Author_Name
            { 
                 get { return author_name; }
                set { author_name= value; }
             }
      }

In your 'Main' class, you will wrote your code as

    class TestSong
    { 
      public static void Main(String[] Args)
      {
          Song _song = new Song(); //create an object for class 'Song'    
          _song.Author_Name = 'John Biley';
          String author = _song.Author_Name;           
          Console.WriteLine("Authorname = {0}"+author);
      }
    }

Point to be noted;

The method you set/get should be public or protected(take care) but strictly shouldnt be private.

Answer 3

These are properties . You would use them like so:

Tom.Title = "Accountant";
string desc = Tom.Description;

But considering they are declared protected their visibility may be a concern.

Answer 4

By the way, in C# 3.5 you can instantiate your object's properties like so:

Person TOM=new Person 
{ 
   title = "My title", ID = 1 
};

But again, properties must be public.

Answer 5

I do not understand what this is unclear

Properties are members that provide a flexible mechanism to read, write, or compute the values of private fields. Properties can be used as though they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily while still providing the safety and flexibility of methods.

In this example, the class TimePeriod stores a time period. Internally the class stores the time in seconds, but a property called Hours is provided that allows a client to specify a time in hours. The accessors for the Hours property perform the conversion between hours and seconds.

Example

class TimePeriod
{
    private double seconds;

    public double Hours
    {
        get { return seconds / 3600; }
        set { seconds = value * 3600; }
    }
}

class Program
{
    static void Main()
    {
        TimePeriod t = new TimePeriod();

        // Assigning the Hours property causes the 'set' accessor to be called.
        t.Hours = 24;

        // Evaluating the Hours property causes the 'get' accessor to be called.
        System.Console.WriteLine("Time in hours: " + t.Hours);
    }
}

Properties Overview

Properties enable a class to expose a public way of getting and setting values, while hiding implementation or verification code.

A get property accessor is used to return the property value, and a set accessor is used to assign a new value. These accessors can have different access levels.

The value keyword is used to define the value being assigned by the set indexer.

Properties that do not implement a set method are read only.

http://msdn.microsoft.com/en-US/library/x9fsa0sw%28v=vs.80%29.aspx

Answer 6

Set them to public. That is, wherever you have the word "protected", change it for the word "public". If you need access control, put it inside, in front of the word 'get' or the word 'set'.

Answer 7

You are not able to access those properties as they are marked as protected meaning:

The type or member can be accessed only by code in the same class or struct, or in a class that is derived from that class.