监视后台任务进度和完成

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重要的 API

了解应用如何识别在进程外运行的后台任务报告的进度和完成情况。 （对于进程内后台任务，可以设置共享变量来表示进度和完成情况。）

可以由应用代码监视后台任务进度和完成情况。 为此，应用订阅已向系统注册的后台任务事件。

创建一个事件处理程序以处理完成的后台任务

步骤 1

创建一个事件处理程序函数以处理完成的后台任务。 该代码需遵循特定的足迹，即获取 IBackgroundTaskRegistration 对象和 BackgroundTaskCompletedEventArgs 对象。

对 OnCompleted 后台任务事件处理程序方法使用以下足迹。

private void OnCompleted(IBackgroundTaskRegistration task, BackgroundTaskCompletedEventArgs args)
{
    // TODO: Add code that deals with background task completion.
}

auto completed{ [this](
        Windows::ApplicationModel::Background::BackgroundTaskRegistration const& /* sender */,
        Windows::ApplicationModel::Background::BackgroundTaskCompletedEventArgs const& /* args */)
{
    // TODO: Add code that deals with background task completion.
} };

auto completed = [this](BackgroundTaskRegistration^ task, BackgroundTaskCompletedEventArgs^ args)
{
    // TODO: Add code that deals with background task completion.
};

步骤 2

向处理后台任务完成的事件处理程序中添加代码。

例如，后台任务示例更新 UI。

private void OnCompleted(IBackgroundTaskRegistration task, BackgroundTaskCompletedEventArgs args)
{
    UpdateUI();
}

auto completed{ [this](
        Windows::ApplicationModel::Background::BackgroundTaskRegistration const& /* sender */,
        Windows::ApplicationModel::Background::BackgroundTaskCompletedEventArgs const& /* args */)
{
    UpdateUI();
} };

auto completed = [this](BackgroundTaskRegistration^ task, BackgroundTaskCompletedEventArgs^ args)
{    
    UpdateUI();
};

创建一个事件处理程序函数以处理后台任务进度。

步骤 1

创建一个事件处理程序函数以处理完成的后台任务。 该代码需遵循特定的足迹，即获取 IBackgroundTaskRegistration 对象和 BackgroundTaskProgressEventArgs 对象：

对 OnProgress 后台任务事件处理程序方法使用以下足迹：

private void OnProgress(IBackgroundTaskRegistration task, BackgroundTaskProgressEventArgs args)
{
    // TODO: Add code that deals with background task progress.
}

auto progress{ [this](
    Windows::ApplicationModel::Background::BackgroundTaskRegistration const& /* sender */,
    Windows::ApplicationModel::Background::BackgroundTaskProgressEventArgs const& /* args */)
{
    // TODO: Add code that deals with background task progress.
} };

auto progress = [this](BackgroundTaskRegistration^ task, BackgroundTaskProgressEventArgs^ args)
{
    // TODO: Add code that deals with background task progress.
};

步骤 2

向处理后台任务完成的事件处理程序中添加代码。

例如，后台任务示例使用通过 args 参数传递的进度状态更新 UI：

private void OnProgress(IBackgroundTaskRegistration task, BackgroundTaskProgressEventArgs args)
{
    var progress = "Progress: " + args.Progress + "%";
    BackgroundTaskSample.SampleBackgroundTaskProgress = progress;
    UpdateUI();
}

auto progress{ [this](
    Windows::ApplicationModel::Background::BackgroundTaskRegistration const& /* sender */,
    Windows::ApplicationModel::Background::BackgroundTaskProgressEventArgs const& args)
{
    winrt::hstring progress{ L"Progress: " + winrt::to_hstring(args.Progress()) + L"%" };
    BackgroundTaskSample::SampleBackgroundTaskProgress = progress;
    UpdateUI();
} };

auto progress = [this](BackgroundTaskRegistration^ task, BackgroundTaskProgressEventArgs^ args)
{
    auto progress = "Progress: " + args->Progress + "%";
    BackgroundTaskSample::SampleBackgroundTaskProgress = progress;
    UpdateUI();
};

使用新的和现有的后台任务注册事件处理程序函数

步骤 1

当应用首次注册后台任务时，应用应该注册以在任务运行（同时应用仍然在前台处于活动状态）时接收它的进度和完成更新。

例如，后台任务示例在它触发的每个后台任务上调用以下函数：

private void AttachProgressAndCompletedHandlers(IBackgroundTaskRegistration task)
{
    task.Progress += new BackgroundTaskProgressEventHandler(OnProgress);
    task.Completed += new BackgroundTaskCompletedEventHandler(OnCompleted);
}

void SampleBackgroundTask::AttachProgressAndCompletedHandlers(Windows::ApplicationModel::Background::IBackgroundTaskRegistration const& task)
{
    auto progress{ [this](
        Windows::ApplicationModel::Background::BackgroundTaskRegistration const& /* sender */,
        Windows::ApplicationModel::Background::BackgroundTaskProgressEventArgs const& args)
    {
        winrt::hstring progress{ L"Progress: " + winrt::to_hstring(args.Progress()) + L"%" };
        BackgroundTaskSample::SampleBackgroundTaskProgress = progress;
        UpdateUI();
    } };

    task.Progress(progress);

    auto completed{ [this](
        Windows::ApplicationModel::Background::BackgroundTaskRegistration const& /* sender */,
        Windows::ApplicationModel::Background::BackgroundTaskCompletedEventArgs const& /* args */)
    {
        UpdateUI();
    } };

    task.Completed(completed);
}

void SampleBackgroundTask::AttachProgressAndCompletedHandlers(IBackgroundTaskRegistration^ task)
{
    auto progress = [this](BackgroundTaskRegistration^ task, BackgroundTaskProgressEventArgs^ args)
    {
        auto progress = "Progress: " + args->Progress + "%";
        BackgroundTaskSample::SampleBackgroundTaskProgress = progress;
        UpdateUI();
    };

    task->Progress += ref new BackgroundTaskProgressEventHandler(progress);

    auto completed = [this](BackgroundTaskRegistration^ task, BackgroundTaskCompletedEventArgs^ args)
    {
        UpdateUI();
    };

    task->Completed += ref new BackgroundTaskCompletedEventHandler(completed);
}

步骤 2

当应用启动或导航到后台任务状态相关的新页面时，它应用获取档期已注册的后台任务列表并将它们与进度和完成事件处理程序函数关联。 应用程序当前已注册的后台任务列表位于 BackgroundTaskRegistration.AllTasks 属性中。

例如，后台任务示例在导航到 SampleBackgroundTask 页面时使用以下代码附加事件处理程序：

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    foreach (var task in BackgroundTaskRegistration.AllTasks)
    {
        if (task.Value.Name == BackgroundTaskSample.SampleBackgroundTaskName)
        {
            AttachProgressAndCompletedHandlers(task.Value);
            BackgroundTaskSample.UpdateBackgroundTaskStatus(BackgroundTaskSample.SampleBackgroundTaskName, true);
        }
    }

    UpdateUI();
}

void SampleBackgroundTask::OnNavigatedTo(Windows::UI::Xaml::Navigation::NavigationEventArgs const& /* e */)
{
    // A pointer back to the main page. This is needed if you want to call methods in MainPage such
    // as NotifyUser().
    m_rootPage = MainPage::Current;

    // Attach progress and completed handlers to any existing tasks.
    auto allTasks{ Windows::ApplicationModel::Background::BackgroundTaskRegistration::AllTasks() };

    for (auto const& task : allTasks)
    {
        if (task.Value().Name() == SampleBackgroundTaskName)
        {
            AttachProgressAndCompletedHandlers(task.Value());
            break;
        }
    }

    UpdateUI();
}

void SampleBackgroundTask::OnNavigatedTo(NavigationEventArgs^ e)
{
    // A pointer back to the main page.  This is needed if you want to call methods in MainPage such
    // as NotifyUser().
    rootPage = MainPage::Current;

    // Attach progress and completed handlers to any existing tasks.
    auto iter = BackgroundTaskRegistration::AllTasks->First();
    auto hascur = iter->HasCurrent;
    while (hascur)
    {
        auto cur = iter->Current->Value;

        if (cur->Name == SampleBackgroundTaskName)
        {
            AttachProgressAndCompletedHandlers(cur);
            break;
        }

        hascur = iter->MoveNext();
    }

    UpdateUI();
}