这对于使用IDisposable处理对象是否正确

Question

我有一个实现IDisposable接口的类.我正在使用webclient使用AsyncDownloadString下载一些数据.

我想知道我是否在构造函数中和Web客户端的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？

否则这是使用IDisposable接口的正确方法吗？

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

有两种正确的方法可以使用IDisposable对象:

1. 把它放在一个using块
   或
2. 将它包装在一个也正确实现IDisposable 的类中,并在处理这个新类时将其处理掉.您现在希望使用using块创建新类的所有实例.

请注意,我说"或",而不是"和".做一个或另一个,但不是两个.

在这里,当您using在构造函数中使用块创建WebClient实例时,您可以在有机会在其他任何地方使用它之前对其进行处置.在这种情况下,您应该只选择选项二.

Answer 2

这大部分都是正确的,除了wc被处理两次并且在处理之后GetBalance总是使用wc!

编辑:具有该更正的版本:

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

    ~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
    }

    private bool isDisposed = false;

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

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