在C＃中带有参数的构造函数中的正确赋值是什么？

Question

What must I choose author or Author after this. ? Other questions what means the icons beside those options one has a "spanner" and the other has two icons something like a long block more other Little that I don't identify what is that Little and what mean those icons? And if I want to use a second constructor in the same class that is a constructor without arguments is ok to make the constructor like the code after the image?

Other question in the next code Is ok the following constructor without arguments? or can be made that way or is something absurd to do that assignment? if I don't want specific default value would be better to set this.author = null; or this.author = ""; or what must be done?

 public Book()
 {
     this.author = Author;
     this.title = Title;
 }

Answer 1

You should understand what is field and what is property.

Fields - keep your data.

Properties - it's accessors to your data, they like methods but with some sintacsic shugar.

When you have such simple class like Book it can look like this:

class Book
{
    public string Title { get; set; }
    public string Author { get; set; }
}

And you can create new book like this:

var book = new Book {Author = "Name", Title = "Some Book"};

C# has autoproperty, so this code:

public string Title { get; set; }

Is the same as this:

private string title;
public string Title
{
    get { return title; }
    set { title = value; }
}

About your question. In case you like keep your code as is. Constructor should be:

public Book(string title, string author)
{
    this.title = title;
    this.author = author;
}

Basically, when you declare some private field or method it's for your class only.

When you declare public property or method (public fields is bad, do not do this unless absolutly necessary), it's for consumers of your class.

Answer 2

A constructor without any parameters is called a default constructor .

You don't have to write a default constructor if you don't want to. For example, if you want Book book = new Book (); to be a syntax error then you shouldn't write a default constructor.

If you do create a default constructor then it should initialize your class instance in some way that makes sense in the context of your program. Think about what book should look like after executing Book book = new Book (); .

You could pick some book and author as the default...

  public Book()
  {
     title = "The Hitchhikers Guide to the Galaxy";
     author = "Douglas Adams";
  }

... or you could use some value that makes clear that the instance hasn't really been initialized...

  public Book()
  {
     title = "<<< title not set >>>";
     author = "<<< author not set >>>";
  }

... or you could use some other suitable value ...

  public Book()
  {
     title = String.Empty;
     author = String.Empty;
  }

... or even do nothing...

  public Book()
  {
  }

Answer 3

In your specific code, the difference of using this.Author or this.author is not much. Generally, I prefer this.Author because later if you add some code in the setter of Book.Author , you may also need to run the additional code, that is why you create a setter.

But your second constructor is wrong:

this.author = Author;

This is equivalent to:

this.author = this.Author

It will assign null to author . You should use the arguments from constructor like your first constructor.

Answer 4

The spanner represents a Property. The blocks represent a field. Setting a field is more efficient than setting a property. Setting the property requires two operations instead of one. Set the field when you can. Setting a property is useful when something has to occur when the property changes. You can add your OnChange code to the setter of the property.