Question

任何人都可以帮助新手C＃初学者吗？我试图调用在同一个类中创建的对象但是使用不同的方法。这两种方法都是从另一个类调用的。以下是简单的代码。我遗漏了方法执行的其他代码。错误表示在第二种方法中无法识别“侦听器”对象。感谢您提供的任何帮助。

// this 1st class calls methods of a 2nd class
public class Lru_operation
{
    // create an object of the 2nd class
    public Lru_Listen LruListen = new Lru_Listen();

    // this method calls two methods from other class   
    public void LruOperation()
    {   
        LruListen.ListenForAag();          // first method call

        LruListen.LruListenAccReq();       // second method call 
    }
}

// this is the 2nd class 
public class Lru_Listen
{
    // 1st method creates an object from a different class (HttpListener)
    public void ListenForAag()
    {
        HttpListener listener = new HttpListener(); 
    }

    // 2nd method calls 1st method's object to perform 
    // a method task from a different class
    public void LruListenAccReq()
    {
        HttpListenerContext context = listener.Getcontext();        
    }
}

Answer 1

为了通过两种不同的方法调用它，两种方法都需要访问该值。由于它们属于同一类型，因此分享listener值的最简单方法是将其设为字段

public class Lru_Listen {
  HttpListener listener;

  public void ListenForAag() {
    listener = new HttpListener(); 
  }

  public void LruListenAccReq() {
    HttpListenerContext context = listener.Getcontext();        
  }
}

Answer 2

问题完全在Lru_Listen类中 - 您声明的变量是ListenForAag成员的本地变量。如果你把它变成一个类级变量（一个字段），你将不会遇到这个问题：

// Make an instance variable:
HttpListener listener;

// 1st method creates an object from a different class (HttpListener)
public void ListenForAag()
{
    // Set the instance variable
    listener = new HttpListener(); 
}

// 2nd method calls 1st method's object to perform 
// a method task from a different class
public void LruListenAccReq()
{
    HttpListenerContext context = listener.Getcontext();        
}

请注意，在这种情况下，最好在构造函数中设置它而不是方法：

// this 1st class calls methods of a 2nd class
public class Lru_operation
{
    // create an object of the 2nd class
    // Note that this can be private, since it's only used in this class
    private Lru_Listen lruListen = new Lru_Listen();

    // this method calls two methods from other class   
    public void LruOperation()
    {   
        // No longer required
        // lruListen.ListenForAag();          // first method call

        lruListen.LruListenAccReq();       // second method call 
    }
}

// this is the 2nd class 
public class Lru_Listen
{
    HttpListener listener;

    // use the constructor
    public Lru_Listen()
    {
        listener = new HttpListener(); 
    }

    public void LruListenAccReq()
    {
        HttpListenerContext context = listener.Getcontext();        
    }
}

这保证了侦听器将始终正确设置，即使该类用户（可能是您）忘记明确调用ListenForArg。

Answer 3

你需要阅读范围。基本上你的监听器不存在，除了在范围内 ListenForAag函数。假设您需要在函数中实例化侦听器。但是你可能会更好地使用构造函数。

public class Lru_Listen
{
 HttpListener listener;
// 1st method creates an object from a different class (HttpListener)
public void ListenForAag()
{
    listener = new HttpListener(); 
}

// 2nd method calls 1st method's object to perform 
// a method task from a different class
public void LruListenAccReq()
{
    HttpListenerContext context = listener.Getcontext();        
}
}

Answer 4

您可以返回侦听器并在第二种方法中接收它。

public HttpListener ListenForAag()
{
    listener = new HttpListener(); 
    return listener;
}

public void LruListenAccReq(HttpListener listener)
{
    HttpListenerContext context = listener.Getcontext();        
}

如何从C＃中的另一个方法调用对象

4 个答案: