创建新线程，传递参数

Question

我想创建一个线程，然后将参数传递给它。但我不知道怎么办。

Thread siteDownloader = new Thread(new ParameterizedThreadStart(GetHTML));

这是我想作为新线程启动的函数。

static string GetHTML(string siteURL)
{
    WebClient webClient = new WebClient();

    try
    {
        string sitePrefix = siteURL.Substring(0, 7);
        if (sitePrefix != "http://")
        {
            siteURL = "http://" + siteURL;
        }
    }
    catch
    {
        siteURL = "http://" + siteURL;
    }

    try
    {
        return webClient.DownloadString(siteURL);
    }
    catch
    {
        return "404";
    }
}

Answer 1

就我个人而言，我总是使用捕获的变量，即

int a = ...
string b = ...
ThreadStart work = delegate {
    var result = DoSomethingInteresting(a, b);
    // push result somewhere; might involve a UI
    // thread switch
};
new Thread(work).Start();

这意味着在构建过程中始终检查其正确性，这与传递对象参数不同。

Answer 2

引用msdn：

public class Work
{
    public static void Main()
    {
        // To start a thread using a shared thread procedure, use
        // the class name and method name when you create the 
        // ParameterizedThreadStart delegate. C# infers the 
        // appropriate delegate creation syntax:
        //    new ParameterizedThreadStart(Work.DoWork)
        //
        Thread newThread = new Thread(Work.DoWork);

        // Use the overload of the Start method that has a
        // parameter of type Object. You can create an object that
        // contains several pieces of data, or you can pass any 
        // reference type or value type. The following code passes
        // the integer value 42.
        //
        newThread.Start(42);

        // To start a thread using an instance method for the thread 
        // procedure, use the instance variable and method name when 
        // you create the ParameterizedThreadStart delegate. C# infers 
        // the appropriate delegate creation syntax:
        //    new ParameterizedThreadStart(w.DoMoreWork)
        //
        Work w = new Work();
        newThread = new Thread(w.DoMoreWork);

        // Pass an object containing data for the thread.
        //
        newThread.Start("The answer.");
    }

    public static void DoWork(object data)
    {
        Console.WriteLine("Static thread procedure. Data='{0}'",
            data);
    }

    public void DoMoreWork(object data)
    {
        Console.WriteLine("Instance thread procedure. Data='{0}'",
            data);
    }
}

这样你就可以看到你创建了以 object 作为参数的方法，并将该参数传递给 Thread 类的 Start 方法

Answer 3

拉法尔的解决方案会起作用，但我不确定你如何从中获得返回值。正如 Martinho 指出的，ParameterizedThreadStart 要求该方法返回 void。尝试使用BackgroundWorker 来代替。

像这样称呼它。

var bw = new BackgroundWorker();
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
bw.RunWorkerAsync(url);

这是 DoWork，基本上是 GetHTML 的修改版本。

static void bw_DoWork(object sender, DoWorkEventArgs e)
{
    WebClient webClient = new WebClient();
    string siteURL = (string)e.Argument;

    try
    {
        string sitePrefix = siteURL.Substring(0, 7);
        if(sitePrefix != "http://")
            siteURL = "http://" + siteURL;
    }
    catch
    {
        siteURL = "http://" + siteURL;
    }

    try
    {
        e.Result = webClient.DownloadString(siteURL);
    }
    catch
    {
        e.Result = "404";
    }
}

最后，在 bw_RunWorkerCompleted 中执行类似的操作

static void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    string result;
    result = (string)e.Result;
    //do something with result
}

Answer 4

您是否查看了 ParametrizedThreadStart 的文档？您需要一个接受对象参数并且不返回任何内容的方法。因此，您需要相应地更改方法签名：

static void GetHTML(object data)
{
    string siteUrl = (string) data; // cast argument to string
    // blah blah
}

然后您需要找出使用返回值的方法。