为什么我的 FormLoad 事件处理程序调用自定义 class' 默认构造函数而不是带参数的构造函数？

Question

我正在为一项任务制作一个基本的 multiclass GUI 程序，我在其中创建了三个自定义 classes，它们继承了抽象 class（ReadingMaterial）和一个界面。我运行遇到的问题是，当我运行它应该传递给每个 class 的构造函数的信息时（我已经包含了 class Online for example) 没有被传递，那些 classes 正在调用它们的默认构造函数，所以我的 GUI 组件显示零和空格而不是填充传递给构造函数的其他信息。为什么它不调用正确的构造函数而不是默认的构造函数？

(GUI 表单部分 class)

public partial class PresentationGUI : Form
{
    private Book book;
    private Magazine magazine;
    private Online online;

    public PresentationGUI()
    {
        InitializeComponent();
    }

    private void rdBtnOnline_CheckedChanged(object sender, EventArgs e)
    {
        txtBxPageCount.Text = online.PageCount.ToString();
        txtBxTitle.Text = online.Title;
        txtBxAuthor.Text = online.Author;
        txtBxURL.Text = online.WebsiteURL;
        txtBxPrintable.Text = online.HardCopyAvailability();

        // ...
    }

    private void PresentationGUI_Load(object sender, EventArgs e)
    {
        book = new Book(1000, "C# Programming", "Barbara Doyle",
            "Cengage", "5th Edition");

        online = new Online(5, "C Sharp (Programming Language)", "Crowd Sourced Author",
                "https://en.wikipedia.org/wiki/C_Sharp_(programming_language)");

        magazine = new Magazine(200, "PC Magazine", "Varied Authors",
                "Ziff Davis", 6, 16);
    }
}

(在线class继承自ReadingMaterial摘要class(下))

public class Online : ReadingMaterial, IPrintable
{
    private string websiteURL;
    public string WebsiteURL { get; set; }

    public Online()
        :base()
    {
        websiteURL = "";
    }

    public Online(int pageCount, string title, string author, string url)
        :base(pageCount, title, author)
    {
        websiteURL = url;
    }

    public string HardCopyAvailability()
    {
        return "Printable";
    }
}

(基础class阅读材料)

public abstract class ReadingMaterial
{
    private int pageCount;
    private string title;
    private string author;

    public int PageCount { get; set; }
    public string Title { get; set; }
    public string Author { get; set; }

    public ReadingMaterial()
    {
        pageCount = 0;
        title = "";
        author = "";
    }

    public ReadingMaterial(int pageCount, string title, string author)
    {
        this.pageCount = pageCount;
        this.title = title;
        this.author = author;
    }
}

Answer 1

不是构造函数的问题。您没有将支持变量连接到属性。要么这样做：

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

    ...
}

或者完全放弃支持变量并使用自动实现的属性。如果您这样做，C# 会自动为您创建一个隐藏的支持变量。

public string Title { get; set; }

并在构造函数中，将参数分配给属性而不是支持变量。

this.Title = title;

为什么我的 FormLoad 事件处理程序调用自定义 class' 默认构造函数而不是带参数的构造函数？

Why does my FormLoad event handler call the custom class' default constructor instead of the one with arguments?

c#

constructor

default-constructor