在析构函数为什么叫处置（假）？ [英] Why call dispose(false) in the destructor?

问题描述

下面是一个典型的Dispose模式例如：

What follows is a typical dispose pattern example:

 public bool IsDisposed { get; private set; }

  #region IDisposable Members

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

  protected virtual void Dispose(bool disposing)
  {
    if (!IsDisposed)
    {
      if (disposing)
      {
        //perform cleanup here
      }

      IsDisposed = true;
    }
  }

  ~MyObject()
  {
    Dispose(false);
  }

我明白了什么处分呢，但我不明白的是为什么你希望中调用析构函数的Dispose（假）？如果你看一下定义，它会什么都不做，那么，为什么会有人这样写代码？那岂不是什么意义，只是不的调用，在析构函数在所有配置？

I understand what dispose does, but what I don't understand is why you would want to call dispose(false) in the destructor? If you look at the definition it would do absolutely nothing, so why would anyone write code like this? Wouldn't it make sense to just not call dispose from the destructor at all?

推荐答案

的终结用作后备如果对象是不是出于某种原因，妥善处置。通常情况下，的Dispose（）方法将被称为从而消除终结联播并把对象变成一个常规管理对象的垃圾收集器可以轻松地删除。

The finalizer is used as a fall-back if the object is not disposed properly for some reason. Normally the Dispose() method would be called which removes the finalizer hookup and turns the object into a regular managed object that the garbage collector easily can remove.

下面是从已经成功的一类MSDN和非托管资源的示例进行清理。

Here is an example from MSDN of a class that has managed and unmanaged resources to clean up.

注意，管理资源仅如果清理处置是事实，但非托管资源始终是清理。

Notice that the managed resources are only cleaned up if disposing is true, but unmanaged resources is always cleaned up.

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.
    private 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);
    }
}

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