C# HttpClient 异步等待 - 无法保证“A”在“B”之前

Question

我正在尝试编写一个 C# 控制台应用程序，它使用 HttpClient 来抓取 web 页。 调用 FunctionOne 时，确保“A”先于“B”写入控制台的最佳方法是什么？ 每当我运行我的代码时，“B”总是写在“A”之前。 先谢谢您的帮助！

public class MyClass
{
    public void FunctionOne(string url)
    {   
        FunctionTwoAsync(url);

        Console.WriteLine("B");
    }

    private async void FunctionTwoAsync(string url)
    {
        var httpClient = new HttpClient();
        var htmlContent = await httpClient.GetStringAsync(url);
        var htmlDocument = new HtmlDocument();
        htmlDocument.LoadHtml(htmlContent);

        Console.WriteLine("A");
    }
}

Answer 1

您的FunctionTwoAsync方法是一种async方法，这意味着该方法是异步的。

当您需要 methode 的结果或需要此方法完成时，您必须对async方法使用await关键字

因此，像这样更改您的代码：

public class MyClass {

public async Task FunctionOne(string url)
{   
    await FunctionTwoAsync(url);

    Console.WriteLine("B");
}

private async Task FunctionTwoAsync(string url)
{
    var httpClient = new HttpClient();
    var htmlContent = await httpClient.GetStringAsync(url);
    var htmlDocument = new HtmlDocument();
    htmlDocument.LoadHtml(htmlContent);

    Console.WriteLine("A");
}
}

Answer 2

要在 B 之前创建 A，您需要等待 FunctionTwoAsync 并使 FunctionOne 成为异步 function

 public async void FunctionOne(string url)
 {   
    await FunctionTwoAsync(url);

    Console.WriteLine("B");
 }

Answer 3

您应该使 FunctionOne 也异步并等待第二个 function 的执行：

public class MyClass
{
    public async Task FunctionOne(string url)
    {   
        await FunctionTwoAsync(url);

        Console.WriteLine("B");
    }

    private async Task FunctionTwoAsync(string url)
    {
        var httpClient = new HttpClient();
        var htmlContent = await httpClient.GetStringAsync(url);
        var htmlDocument = new HtmlDocument();
        htmlDocument.LoadHtml(htmlContent);

        Console.WriteLine("A");
    }
}