正确实施 IDisposable

Question

在我的课程中，我实现IDisposable 如下：

public class User : IDisposable
{
    public int id { get; protected set; }
    public string name { get; protected set; }
    public string pass { get; protected set; }

    public User(int UserID)
    {
        id = UserID;
    }
    public User(string Username, string Password)
    {
        name = Username;
        pass = Password;
    }

    // Other functions go here...

    public void Dispose()
    {
        // Clear all property values that maybe have been set
        // when the class was instantiated
        id = 0;
        name = String.Empty;
        pass = String.Empty;
    }
}

在 VS2012 中，我的代码分析说要正确实现 IDisposable，但我不确定我在这里做错了什么。
具体文字如下：

CA1063 正确实现 IDisposable 在“用户”上提供可覆盖的 Dispose(bool) 实现或将类型标记为密封。对 Dispose(false) 的调用应该只清理本机资源。对 Dispose(true) 的调用应该清理托管资源和本机资源。 stman User.cs 10

供参考：CA1063: Implement IDisposable correctly

我已经阅读了这个页面，但恐怕我不太明白这里需要做什么。

如果有人能用更通俗的语言解释问题是什么和/或应该如何实现IDisposable，那真的很有帮助！

Answer 1

这将是正确的实现，尽管我在您发布的代码中看不到您需要处理的任何内容。您只需要在以下情况下实现IDisposable：

1. 您有非托管资源
2. 您坚持对本身是一次性的事物的引用。

您发布的代码中的任何内容都不需要处理。

public class User : IDisposable
{
    public int id { get; protected set; }
    public string name { get; protected set; }
    public string pass { get; protected set; }

    public User(int userID)
    {
        id = userID;
    }
    public User(string Username, string Password)
    {
        name = Username;
        pass = Password;
    }

    // Other functions go here...

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (disposing) 
        {
            // free managed resources
        }
        // free native resources if there are any.
    }
}

Answer 2

首先，您不需要“清理”strings 和 ints - 它们将由垃圾收集器自动处理。在Dispose 中唯一需要清理的是非托管资源或实现IDisposable 的托管资源。

但是，假设这只是一个学习练习，实现IDisposable 的推荐方法是添加一个“安全捕获”以确保任何资源都不会被两次处理： p>

public void Dispose()
{
    Dispose(true);

    // Use SupressFinalize in case a subclass 
    // of this type implements a finalizer.
    GC.SuppressFinalize(this);   
}
protected virtual void Dispose(bool disposing)
{
    if (!_disposed)
    {
        if (disposing) 
        {
            // Clear all property values that maybe have been set
            // when the class was instantiated
            id = 0;
            name = String.Empty;
            pass = String.Empty;
        }

        // Indicate that the instance has been disposed.
        _disposed = true;   
    }
}

Answer 3

以下示例显示了实现IDisposable 接口的一般最佳实践。 Reference

请记住，只有当您的类中有非托管资源时，您才需要析构函数（终结器）。如果你添加了析构函数，你应该在 Dispose 中抑制 Finalization，否则会导致你的对象在内存中驻留两个垃圾周期（注意：Read how Finalization works）。下面的例子详细说明了以上所有内容。

public class DisposeExample
{
    // A base class that implements IDisposable. 
    // By implementing IDisposable, you are announcing that 
    // instances of this type allocate scarce resources. 
    public class MyResource: IDisposable
    {
        // Pointer to an external unmanaged resource. 
        private IntPtr handle;
        // Other managed resource this class uses. 
        private Component component = new Component();
        // Track whether Dispose has been called. 
        private bool disposed = false;

        // The class constructor. 
        public MyResource(IntPtr handle)
        {
            this.handle = handle;
        }

        // Implement IDisposable. 
        // Do not make this method virtual. 
        // A derived class should not be able to override this method. 
        public void Dispose()
        {
            Dispose(true);
            // This object will be cleaned up by the Dispose method. 
            // Therefore, you should call GC.SupressFinalize to 
            // take this object off the finalization queue 
            // and prevent finalization code for this object 
            // from executing a second time.
            GC.SuppressFinalize(this);
        }

        // Dispose(bool disposing) executes in two distinct scenarios. 
        // If disposing equals true, the method has been called directly 
        // or indirectly by a user's code. Managed and unmanaged resources 
        // can be disposed. 
        // If disposing equals false, the method has been called by the 
        // runtime from inside the finalizer and you should not reference 
        // other objects. Only unmanaged resources can be disposed. 
        protected virtual void Dispose(bool disposing)
        {
            // Check to see if Dispose has already been called. 
            if(!this.disposed)
            {
                // If disposing equals true, dispose all managed 
                // and unmanaged resources. 
                if(disposing)
                {
                    // Dispose managed resources.
                    component.Dispose();
                }

                // Call the appropriate methods to clean up 
                // unmanaged resources here. 
                // If disposing is false, 
                // only the following code is executed.
                CloseHandle(handle);
                handle = IntPtr.Zero;

                // Note disposing has been done.
                disposed = true;

            }
        }

        // Use interop to call the method necessary 
        // to clean up the unmanaged resource.
        [System.Runtime.InteropServices.DllImport("Kernel32")]
        private extern static Boolean CloseHandle(IntPtr handle);

        // Use C# destructor syntax for finalization code. 
        // This destructor will run only if the Dispose method 
        // does not get called. 
        // It gives your base class the opportunity to finalize. 
        // Do not provide destructors in types derived from this class.
        ~MyResource()
        {
            // Do not re-create Dispose clean-up code here. 
            // Calling Dispose(false) is optimal in terms of 
            // readability and maintainability.
            Dispose(false);
        }
    }
    public static void Main()
    {
        // Insert code here to create 
        // and use the MyResource object.
    }
}

Answer 4

IDisposable 的存在为您提供了一种方法来清理垃圾收集器不会自动清理的非托管资源。

您正在“清理”的所有资源都是托管资源，因此您的 Dispose 方法什么也没做。你的班级根本不应该实现IDisposable。垃圾收集器会自行处理所有这些字段。

Answer 5

您需要像这样使用一次性模式：

private bool _disposed = false;

protected virtual void Dispose(bool disposing)
{
    if (!_disposed)
    {
        if (disposing)
        {
            // Dispose any managed objects
            // ...
        }

        // Now disposed of any unmanaged objects
        // ...

        _disposed = true;
    }
}

public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this);  
}

// Destructor
~YourClassName()
{
    Dispose(false);
}

Answer 6

您无需将User 类设置为IDisposable，因为该类不获取任何非托管资源（文件、数据库连接等）。通常，我们将类标记为 IDisposable 如果他们至少有一个 IDisposable 字段或/和属性。 在实现IDisposable时，最好按照微软的典型方案：

public class User: IDisposable {
  ...
  protected virtual void Dispose(Boolean disposing) {
    if (disposing) {
      // There's no need to set zero empty values to fields 
      // id = 0;
      // name = String.Empty;
      // pass = String.Empty;

      //TODO: free your true resources here (usually IDisposable fields)
    }
  }

  public void Dispose() {
    Dispose(true);

    GC.SuppressFinalize(this);
  } 
}

Answer 7

Idisposable 在您需要确定性（已确认）垃圾回收时实施。

class Users : IDisposable
    {
        ~Users()
        {
            Dispose(false);
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
            // This method will remove current object from garbage collector's queue 
            // and stop calling finilize method twice 
        }    

        public void Dispose(bool disposer)
        {
            if (disposer)
            {
                // dispose the managed objects
            }
            // dispose the unmanaged objects
        }
    }

在创建和使用Users类时使用“using”块来避免显式调用dispose方法：

using (Users _user = new Users())
            {
                // do user related work
            }

using 块创建的 Users 对象的末尾将通过 dispose 方法的隐式调用进行处理。

Answer 8

我看到了很多 Microsoft Dispose 模式的示例，这确实是一种反模式。正如许多人指出的那样，问题中的代码根本不需要 IDisposable。但是，如果您要在哪里实现它，请不要使用 Microsoft 模式。更好的答案是遵循本文中的建议：

https://www.codeproject.com/Articles/29534/IDisposable-What-Your-Mother-Never-Told-You-About

唯一可能有用的另一件事是抑制代码分析警告...https://docs.microsoft.com/en-us/visualstudio/code-quality/in-source-suppression-overview?view=vs-2017