c# - 这对于使用 IDisposable 处理对象是否正确

Question

我有一个实现 IDisposable 接口(interface)的类。我正在使用网络客户端使用 AsyncDownloadString 下载一些数据。

我想知道我是否在 Web 客户端的构造函数和 using 语句中正确声明了我的事件处理程序？这是在 Dispose 方法中删除事件处理程序的正确方法吗？

否决这是使用 IDisposable 接口(interface)的正确方法吗？

public class Balance : IDisposable
{
    //Constructor
    WebClient wc;
    public Balance()
    {
        using (wc = new WebClient())
        {
            //Create event handler for the progress changed and download completed events
            wc.DownloadProgressChanged += new DownloadProgressChangedEventHandler(wc_DownloadProgressChanged);
            wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);
        }
    }

    ~Balance()
    {
        this.Dispose(false);
    }

    //Get the current balance for the user that is logged in.
    //If the balance returned from the server is NULL display error to the user.
    //Null could occur if the DB has been stopped or the server is down.       
    public void GetBalance(string sipUsername)
    {
        //Remove the underscore ( _ ) from the username, as this is not needed to get the balance.
        sipUsername = sipUsername.Remove(0, 1);

        string strURL =
            string.Format("https://www.xxxxxxx.com", 
            sipUsername);

        //Download only when the webclient is not busy.
        if (!wc.IsBusy)
        { 
            // Download the current balance.
            wc.DownloadStringAsync(new Uri(strURL));             
        }
        else
        {
            Console.Write("Busy please try again");
        }
    }

    //return and display the balance after the download has fully completed
    void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
    {
        //Pass the result to the event handler
    }

    //Dispose of the balance object
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    //Remove the event handlers
    private bool isDisposed = false;
    private void Dispose(bool disposing)
    {
        if (!this.isDisposed)
        {
            if (disposing)
            {
                wc.DownloadProgressChanged -= new DownloadProgressChangedEventHandler(wc_DownloadProgressChanged);
                wc.DownloadStringCompleted -= new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);

                wc.Dispose();
            }               
            isDisposed = true;
        }
    }
}

Answer 1

有两种使用 IDisposable 对象的正确方法:

1. 将其放在using block 中
   或
2. 将它包装在一个同样正确实现 IDisposable 的类中，并在处理这个新类时将其处理掉。您现在希望新类的所有实例都是使用 using block 创建的。

请注意，我说的是“或”，而不是“和”。做一个或另一个，但不能同时做。

在这里，当您在构造函数中使用 using block 创建 WebClient 实例时，您会在有机会在其他任何地方使用它之前将其处置掉。在这种情况下，您应该只执行选项二。