我正在尝试实现一个长期运行的后台进程，定期报告其进度，以更新 UWP 应用程序中的 UI。我怎样才能做到这一点？我已经看到了几个有用的主题，但没有一个包含所有内容，而且我无法将它们全部放在一起。
例如，假设用户选择了一个非常大的文件，并且应用程序正在读取和/或操作文件中的数据。用户单击一个按钮，该按钮会使用用户选择的文件中的数据填充存储在页面上的列表。
PART 1
页面和按钮的单击事件处理程序如下所示：
public sealed partial class MyPage : Page
{
public List<DataRecord> DataRecords { get; set; }
private DateTime LastUpdate;
public MyPage()
{
this.InitializeComponent();
this.DataRecords = new List<DataRecord>();
this.LastUpdate = DateTime.Now;
// Subscribe to the event handler for updates.
MyStorageWrapper.MyEvent += this.UpdateUI;
}
private async void LoadButton_Click(object sender, RoutedEventArgs e)
{
StorageFile pickedFile = // … obtained from FileOpenPicker.
if (pickedFile != null)
{
this.DataRecords = await MyStorageWrapper.GetDataAsync(pickedFile);
}
}
private void UpdateUI(long lineCount)
{
// This time check prevents the UI from updating so frequently
// that it becomes unresponsive as a result.
DateTime now = DateTime.Now;
if ((now - this.LastUpdate).Milliseconds > 3000)
{
// This updates a textblock to display the count, but could also
// update a progress bar or progress ring in here.
this.MessageTextBlock.Text = "Count: " + lineCount;
this.LastUpdate = now;
}
}
}
里面的MyStorageWrapper class:
public static class MyStorageWrapper
{
public delegate void MyEventHandler(long lineCount);
public static event MyEventHandler MyEvent;
private static void RaiseMyEvent(long lineCount)
{
// Ensure that something is listening to the event.
if (MyStorageWrapper.MyEvent!= null)
{
// Call the listening event handlers.
MyStorageWrapper.MyEvent(lineCount);
}
}
public static async Task<List<DataRecord>> GetDataAsync(StorageFile file)
{
List<DataRecord> recordsList = new List<DataRecord>();
using (Stream stream = await file.OpenStreamForReadAsync())
{
using (StreamReader reader = new StreamReader(stream))
{
while (!reader.EndOfStream)
{
string line = reader.ReadLine();
// Does its parsing here, and constructs a single DataRecord …
recordsList.Add(dataRecord);
// Raises an event.
MyStorageWrapper.RaiseMyEvent(recordsList.Count);
}
}
}
return recordsList;
}
}
我从以下获得的时间检查代码this https://stephenhaunts.com/2014/10/14/using-async-and-await-to-update-the-ui-thread/.
正如所写，此代码使应用程序对大文件没有响应（我在大约 850 万行的文本文件上进行了测试）。我以为添加async and await to the GetDataAsync()调用会阻止这种情况吗？这不是在 UI 线程之外的线程上工作吗？通过 Visual Studio 中的调试模式，我已验证程序正在按预期进行...它只是占用了 UI 线程，使应用程序无响应（请参阅Microsoft 提供的有关 UI 线程和异步编程的页面 https://learn.microsoft.com/en-us/windows/uwp/debug-test-perf/keep-the-ui-thread-responsive).
PART 2
我已经成功实现了一个异步、长时间运行的进程，该进程在单独的线程上运行，并且仍然定期更新 UI...但此解决方案不允许返回值 - 特别是第 1 部分中的行：
this.DataRecords = await MyStorageWrapper.GetDataAsync(pickedFile);
下面是我之前的成功实施（为简洁起见，省略了大部分内容）。有没有办法调整它以允许返回值？
In a Page class:
public sealed partial class MyPage : Page
{
public Generator MyGenerator { get; set; }
public MyPage()
{
this.InitializeComponent();
this.MyGenerator = new Generator();
}
private void StartButton_Click(object sender, RoutedEventArgs e)
{
this.MyGenerator.ProgressUpdate += async (s, f) => await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, delegate ()
{
// Updates UI elements on the page from here.
}
this.MyGenerator.Start();
}
private void StopButton_Click(object sender, RoutedEventArgs e)
{
this.MyGenerator.Stop();
}
}
并且在Generator class:
public class Generator
{
private CancellationTokenSource cancellationTokenSource;
public event EventHandler<GeneratorStatus> ProgressUpdate;
public Generator()
{
this.cancellationTokenSource = new CancellationTokenSource();
}
public void Start()
{
Task task = Task.Run(() =>
{
while(true)
{
// Throw an Operation Cancelled exception if the task is cancelled.
this.cancellationTokenSource.Token.ThrowIfCancellationRequested();
// Does stuff here.
// Finally raise the event (assume that 'args' is the correct args and datatypes).
this.ProgressUpdate.Raise(this, new GeneratorStatus(args));
}
}, this.cancellationTokenSource.Token);
}
public void Stop()
{
this.cancellationTokenSource.Cancel();
}
}
最后，还有两个支持类ProgressUpdate event:
public class GeneratorStatus : EventArgs
{
// This class can contain a handful of properties; only one shown.
public int number { get; private set; }
public GeneratorStatus(int n)
{
this.number = n;
}
}
static class EventExtensions
{
public static void Raise(this EventHandler<GeneratorStatus> theEvent, object sender, GeneratorStatus args)
{
theEvent?.Invoke(sender, args);
}
}
