确定ProgressBar显示使用Windows :: Web :: Http :: HttpClient下载文件的进度 [英] Determinate ProgressBar showing progress of downloading a file with Windows::Web::Http::HttpClient

问题描述

我想在我的应用程序（XAML + C ++）中显示一个确定的ProgressBar控件，显示下载文件的进度。现在我只实现了不确定的ProgressBar控件。我使用Windows :: Web :: Http :: HttpClient使用以下代码创建异步
下载任务：

 try 
 {
 //执行异步GET。我们需要将use_current（）与continuation一起使用，因为任务在
 //后台线程上完成，我们需要在UI线程上运行以更新UI。 
 OperationProgress-> IsIndeterminate = true; 
 OperationProgress->可见性= Windows :: UI :: Xaml ::可见性::可见; 
 
 create_task（m_httpClient-> GetAsync（resourceAddress），m_cancellationTokenSource.get_token（））。then（[this，pltfmstrFilename]（HttpResponseMessage ^ response）
 {
 //抛出如果HTTP响应的IsSuccessStatusCode属性为false，则为异常。
 response-> EnsureSuccessStatusCode（）; 
 
 //将内容读入本地缓冲区
返回create_task（响应 - > Content-> ReadAsBufferAsync（），m_cancellationTokenSource.get_token（））。then（
 [this，pltfmstrFilename，response]（IBuffer ^ contentBuffer）
 {
 //保存缓冲区内容到本地文件
 if（response-> StatusCode == HttpStatusCode :: Ok）
 {
 StorageFolder ^ tempFolder; 
 tempFolder = ApplicationData :: Current-> TemporaryFolder ; 
 create_task（tempFolder-> CreateFileA sync（pltfmstrFilename，CreationCollisionOption :: ReplaceExisting））。then（[this，contentBuffer]（StorageFile ^ file）
 {
 if（file）{
 //保存下载的内部代码数据到文件
 //为了清楚起见，这里省略了
} 
}，task_continuation_context :: use_current（））; 
} 
}，task_continuation_context :: use_current（））; 
}，task_continuation_context :: use_current（））。then（[=]（task< void> previousTask）
 {
 try 
 {
 OperationProgress-> Visibility = Windows :: UI :: Xaml :: Visibility :: Collapsed; 
 //检查以前的任何任务是否引发异常。
 previousTask.get（）; 
 NotifyUser（" Task completed" ;）; 
} 
 catch（const task_canceled&）
 {
 NotifyUser（"任务取消。"）; 
} 
 catch（异常） ^ ex）
 {
 NotifyUser（" Error：" + ex-> Message）; 
} 
}，task_continuation_context :: use_current（））; 
} 
 catch（Exception ^ ex）
 {
 OperationProgress-> Visibility = Windows :: UI :: Xaml :: Visibility :: Collapsed; 
 NotifyUser（" Error：" + ex-> Message）; 
} 

使用确定的ProgressBar控件可以提供更好的用户体验。有人可以帮忙吗？谢谢。

解决方案

HttpClient GetAsync方法有一个报告进度的重载。  也许这会有所帮助

https：// msdn .microsoft.com / EN-US /库/窗/应用/ dn298645

I want to show a determinate ProgressBar control in my app (XAML + C++) showing progress of downloading a file. For now I have only implemented the indeterminate ProgressBar control. I use Windows::Web::Http::HttpClient to create an asynchronous download task using the code below:

    try
    {
        // Do an asynchronous GET.  We need to use use_current() with the continuations since the tasks are completed on
        // background threads and we need to run on the UI thread to update the UI.
        OperationProgress->IsIndeterminate = true;
        OperationProgress->Visibility = Windows::UI::Xaml::Visibility::Visible;

        create_task(m_httpClient->GetAsync(resourceAddress), m_cancellationTokenSource.get_token()).then([this, pltfmstrFilename](HttpResponseMessage^ response)
        {
            // Throws an exception if the IsSuccessStatusCode property for the HTTP response is false.
            response->EnsureSuccessStatusCode();

            // Read the content into a local buffer
            return create_task(response->Content->ReadAsBufferAsync(), m_cancellationTokenSource.get_token()).then(
                [this,pltfmstrFilename,response](IBuffer^ contentBuffer)
            {
                // Save the buffer content to a local file
                if (response->StatusCode == HttpStatusCode::Ok)
                {
                    StorageFolder^ tempFolder;
                    tempFolder = ApplicationData::Current->TemporaryFolder;
                    create_task(tempFolder->CreateFileAsync(pltfmstrFilename, CreationCollisionOption::ReplaceExisting)).then([this, contentBuffer](StorageFile^ file)
                    {
                        if ( file ) {
                            // in-house code to save downloaded data to a file 
                            // omitted here for clarity
                        }
                    }, task_continuation_context::use_current());
                }
            }, task_continuation_context::use_current());
        }, task_continuation_context::use_current()).then([=](task<void> previousTask)
        {
            try
            {
                OperationProgress->Visibility = Windows::UI::Xaml::Visibility::Collapsed;
                // Check if any previous task threw an exception.
                previousTask.get();
                NotifyUser("Task completed");
            }
            catch (const task_canceled&)
            {
                NotifyUser("Task canceled.");
            }
            catch (Exception^ ex)
            {
                NotifyUser("Error: " + ex->Message);
            }
        }, task_continuation_context::use_current());
    }
    catch (Exception^ ex)
    {
        OperationProgress->Visibility = Windows::UI::Xaml::Visibility::Collapsed;
        NotifyUser("Error: " + ex->Message);
    }

It would be better to use a determinate ProgressBar control that offers better user experience. Could someone help? Thanks.

解决方案

The HttpClient GetAsync method has an overload that reports progress.  Maybe that will help

https://msdn.microsoft.com/en-us/library/windows/apps/dn298645

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