正确实现IDisposable

Question

在我的类中,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Dispose(bool)的可覆盖实现,或将类型标记为已密封.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和本机资源.stman User.cs 10

供参考:CA1063:正确实施IDisposable

我已经阅读了这个页面,但是我担心我真的不明白这里需要做些什么.

如果任何人都可以用更多的术语来解释问题是什么和/或IDisposable应该如何实现,这将真的有帮助!

Answer 1

这将是正确的实现,虽然我没有看到您需要在您发布的代码中处置任何内容.您只需要在以下时间实施IDisposable:

1. 您有非托管资源
2. 你正在坚持引用本身就是一次性的东西.

您发布的代码中没有任何内容需要处理.

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,你不需要"清理" strings和int- 它们将由垃圾收集器自动处理.唯一需要清理的Dispose是非托管资源或实施的托管资源IDisposable.

但是,假设这只是一个学习练习,推荐的实施方法IDisposable是添加"安全捕获"以确保任何资源不会被处置两次:

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.参考

请记住,只有在类中有非托管资源时才需要析构函数(终结器).如果添加析构函数,则应该在Dispose中禁止Finalization,否则会导致对象驻留在内存中两个垃圾循环(注意:阅读Finalization的工作原理).下面的例子详细说明了上述内容

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存在以提供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方法无需任何操作.你的班级根本不应该实施IDisposable.垃圾收集器将自行处理所有这些字段.

Answer 5

你需要像这样使用Disposable Pattern:

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

由于类没有获取任何非托管资源(文件,数据库连接等),因此您无需执行User类.通常,我们将类标记为 至少具有一个字段或/和属性.在实施时,最好根据微软的典型方案:IDisposableIDisposableIDisposableIDisposable

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);
  } 
}