在Dispose中清空"using"语句

public class MyClass : IDisposable
{
    private bool disposed = false;
    private System.IO.StreamReader reader;

    public MyClass()
    {
        reader = new System.IO.StreamReader("file.txt");
    }

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

    protected virtual void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
            {
                // 清空using语句
                if (reader != null)
                {
                    reader.Dispose();
                    reader = null;
                }
            }

            disposed = true;
        }
    }
}