这是启动匿名任务并继续 ui 线程的好方法吗？

Question

自从我处理任务和 lambda 表达式以来已经有一段时间了。这是运行使用 lambda 表达式的匿名任务然后在任务完成后在 UI 线程上运行代码的好方法吗？

private void btn_mods_Click(object sender, RoutedEventArgs e)
{
    function_buttons_stackpanel.IsEnabled = false;
    Loading();
    Task task = new Task(() => {
        if (IsServiceIsUp() != false)
        {
            webServiceMods = JsonConvert.DeserializeObject(_webServiceResponse).mods;
            webServiceBaseUrl = JsonConvert.DeserializeObject(_webServiceResponse).basePath;
            Console.Write(webServiceBaseUrl);

        }
    });
    task.Start();
    task.ContinueWith((foo) =>
    {
        FinishedLoading();
        function_buttons_stackpanel.IsEnabled = true;
    }, TaskScheduler.FromCurrentSynchronizationContext());

}

private void Loading()
{
    img_loading.Visibility = Visibility.Visible;
}

private void FinishedLoading()
{
    img_loading.Visibility = Visibility.Collapsed;
}

我试图直接链接 task.Start，但这给了我一个错误 Cannot Implicitly convert type void to System.Threading.Tasks.Task。

基本上我想做的是将整个过程从头到尾串联起来。

Task task = new Task(() => {
    if (IsServiceIsUp() != false)
    {
        webServiceMods = JsonConvert.DeserializeObject(_webServiceResponse).mods;
        webServiceBaseUrl = JsonConvert.DeserializeObject(_webServiceResponse).basePath;
        Console.Write(webServiceBaseUrl);

    }
}).Start();

在 PHP 我会做这样的事情：

$task = new Task(() => {
    if (IsServiceIsUp() != false)
    {
        $webServiceMods = JsonConvert::DeserializeObject($_webServiceResponse).mods;
        $webServiceBaseUrl = JsonConvert::DeserializeObject($_webServiceResponse).basePath;
        Console::Write($webServiceBaseUrl);

    }
})
->Start()
->ContinueWith(($foo) =>
{
    FinishedLoading();
    $function_buttons_stackpanel.IsEnabled = true;
}, TaskScheduler::FromCurrentSynchronizationContext());

这可能吗？如果是这样，有什么理由不这样做吗？如果有更好的方法可以举个例子吗？

谢谢！

Answer 1

您可以使用 async-await:

private async void btn_mods_Click(object sender, RoutedEventArgs e)
{
    if (!IsServiceIsUp())
        return;

    function_buttons_stackpanel.IsEnabled = false;
    Loading();
    await Task.Run(() => 
    {
        var result = JsonConvert.DeserializeObject(_webServiceResponse);
        Console.Write(result.webServiceBaseUrl);
    });

    FinishedLoading();
    function_buttons_stackpanel.IsEnabled = true;
}

就性能而言，我不太确定您是否需要使用线程池线程来反序列化 JSON。我肯定会测试此代码以确定它是否值得。

Answer 2

如果您将事件处理程序声明为异步函数，那么您不必启动任务，它已经异步运行。

All async functions should return Task instead of void and Task<TResult> instead of TResult. The only exception is the event handler. The event handler returns void

在适当的异步等待中，这将如下所示：

private async void btn_mods_Click(object sender, RoutedEventArgs e)
{
    function_buttons_stackpanel.IsEnabled = false;
    Loading();
    if (IsServiceIsUp())
    {   // The service is up, start the deserialization
        // because this function is async, you can call other async functions
        // without having to start a task
        // The UI remains responsive
        webServiceMods = await JsonConvert.DeserializeObjectAsync(_webServiceResponse).mods;
        // because of the await above, the second task is started after the first is finished:
        webServiceBaseUrl = await JsonConvert.DeserializeObjectAsync(_webServiceResponse).basePath;
        // because of the await the second task is also finished            
        Console.Write(webServiceBaseUrl);
        FinishedLoading();
        function_buttons_stackpanel.IsEnabled = true;
    }
}

By making your event handler async your code will make full usage of async-await. Your code would look much neater without the magic of continueWith and other Task related functions from before the async-await era.

最后一点：下面的代码看起来很傻而且没有必要困难：

if (IsServiceIsUp() != false) ...

这当然应该是：

if (IsServiceIsUp()) ...

这是启动匿名任务并继续 ui 线程的好方法吗？

Is this a good way to start a anonymous task and continue with ui thread?

c#

async-await

task-parallel-library

.net-4.5.2