2个实例类尝试一起工作时引用为空

Question

main

class Program
{
    static void Main(string[] args)
    {
        Worker worker = new Worker();
        worker.Start();

        Console.ReadLine();
    }
}

Worker类

    public Worker()
    {

    }

    public Navigator Navigator;
    public Scraper Scraper;

    public void ResetVariables()
    {
        Navigator = new Navigator(this);
        Scraper = new Scraper(this);
    }

    public void Start()
    {
        ResetVariables();
        Navigator.SetHtml();
    }

Navigator类

    private Worker Worker;
    private Scraper Scraper;

    public string Html;

    public Navigator()
    {

    }

    public Navigator(Worker worker)
    {
        Worker = worker;
        Scraper = worker.Scraper;
    }

    public void SetHtml()
    {
        Html = "navigator has changed its html";
        Scraper.ReadHtmlFromNavigator(); //CAUSES NULL REFERENCE IF CALLED INISIDE THIS METHOD
    }

Scraper类

    private Worker Worker;
    private Navigator Navigator;

    public Scraper()
    {

    }

    public Scraper(Worker worker)
    {
        Worker = worker;
        Navigator = Worker.Navigator;
    }

    public void ReadHtmlFromNavigator()
    {
        Console.WriteLine("scraper reading html from navigator: " + Navigator.Html);
    }

当我从导航器内部调用Scraper.ReadHtmlFromNavigator()时，我得到了一个空引用，但是如果我从worker类调用它，它工作得很好：

public void Start()
    {
        ResetVariables();
        Navigator.SetHtml();
        Scraper.ReadHtmlFromNavigator();
    }

然后我得到了输出：

scraper reading html from navigator: navigator has changed its html

Answer 1

快速回答-不要在导航器中存储对导航器的引用，也不要在导航器中存储对导航器的引用。改为使用对Worker的引用。

在SetHtml方法中，调用Worker.Scraper.ReadHtmlFromNavigator()而不是Scraper.ReadHtmlFromNavigator()

更新:如果你不想每次都输入Woker.XXX，你可以创建一些快捷方式：

private Navigator Navigator { get { return Worker.Navigator; } }
private Navigator Scraper{ get { return Worker.Scraper; } }

Answer 2

在创建抓取器之前，您首先要构建一个新的导航器：

public void ResetVariables()
{
    Navigator = new Navigator(this);
    Scraper = new Scraper(this);
}

因此，您的导航器构造函数将其scraper变量设置为一个尚不存在的worker.scraper。

简单地改变一下顺序，你就应该没问题了：

public void ResetVariables()
{
    Scraper = new Scraper(this);
    Navigator = new Navigator(this);
}

不过，一般来说，请重新考虑如何设置应用程序。这种没有文档记录的强制性序列会产生问题，并且是一种代码气味。