WPF C＃：使用任務

Question

我已經閱讀了幾個不同的帖子，我真的無法理解這個！

我有以下類，當用戶選擇了一個驅動器並設置DriveInfo sel ，運行DoUpload方法，並將DoUpload圖像轉換為字節格式。

現在這需要幾秒鍾在我的機器上，但是更多的圖像和更慢的機器可能需要更長的時間，所以我想在另一個線程上執行此操作，但每次轉換圖像時，我想通知UI，在我的情況下我想要更新以下屬性：縮略圖，文件名，步驟，UploadProgress。

同樣，我想在每次轉換圖像時更新上面的屬性，如何使用Task API執行此操作？

這是班級：

public class UploadInitiation : Common.NotifyUIBase
    {
        #region Public Properties
        /// <summary>
        /// File lists
        /// </summary>
        /// public ObservableCollection<BitmapImage> Thumbnail_Bitmaps { get; set; } = new ObservableCollection<BitmapImage>();
        public ObservableCollection<ByteImage> Thumbnails { get; set; } = new ObservableCollection<ByteImage>();
        public ObservableCollection<NFile> Filenames { get; set; } = new ObservableCollection<NFile>();

        /// <summary>
        /// Updates
        /// </summary>
        public ObservableCollection<UploadStep> Steps { get; set; } = new ObservableCollection<UploadStep>();
        public int UploadProgress { get; set; } = 45;
        public string UploadTask { get; set; } = "Idle...";
        public bool UploadEnabled { get; set; } = false;

        private bool _uploadBegin;
        public bool UploadBegin
        {
            set { _uploadBegin = value; RaisePropertyChanged(); }
            get { return _uploadBegin; }
        }
        #endregion END Public Properties

        public UploadInitiation()
        {
            // Populate steps required, ensure upload returns UI updates
            Steps.Add(new UploadStep { Message = "First task...", Complete = true, Error = null });
            Steps.Add(new UploadStep { Message = "Error testing task...", Complete = false, Error = "testing error" });
            Steps.Add(new UploadStep { Message = "Seperate upload to new thread...", Complete = false, Error = null });
            Steps.Add(new UploadStep { Message = "Generate new file names...", Complete = false, Error = null });
            Steps.Add(new UploadStep { Message = "Render Thumbnails, add to database...", Complete = false, Error = null });
            Steps.Add(new UploadStep { Message = "Move images ready for print...", Complete = false, Error = null });
        }

        /// <summary>
        /// This Method will perform the upload on a seperate thread.
        /// Report progress back by updating public properties of this class.
        /// </summary>
        /// <param name="sel"></param>
        public void DoUpload(DriveInfo sel)
        {
            // Check that there is a device selected
            if (sel != null)
            {
                // Generate List of images to upload
                var files = Directory.EnumerateFiles(sel.Name, "*.*", SearchOption.AllDirectories)
                    .Where(s => s.EndsWith(".jpeg") || s.EndsWith(".jpg") || s.EndsWith(".png"));

                if (files.Count() > 0)
                {
                    // Manage each image
                    foreach (string item in files)
                    {
                        // Generate thumbnail byte array
                        Thumbnails.Add(new ByteImage { Image = GenerateThumbnailBinary(item) });
                    }
                    foreach (string item in files)
                    {
                        // Generate new name
                        Filenames.Add(
                            new NFile
                            {
                                OldName = Path.GetFileNameWithoutExtension(item),
                                NewName = Common.Security.KeyGenerator.GetUniqueKey(32)
                            });
                    }
                }
            }
        }

        public byte[] GenerateThumbnailBinary(string loc)
        {
            BitmapImage image = new BitmapImage(new Uri(loc));

            Stream stream = File.OpenRead(loc);
            byte[] binaryImage = new byte[stream.Length];
            stream.Read(binaryImage,0,(int)stream.Length);

            return binaryImage;
        }

Answer 1

有一個內置的類Progress ，可以向UI線程報告進度。

public async void StartProcessingButton_Click(object sender, EventArgs e)
{
  // The Progress<T> constructor captures our UI context,
  //  so the lambda will be run on the UI thread.
  var progress = new Progress<int>(percent =>
  {
    textBox1.Text = percent + "%";
  });

  // DoProcessing is run on the thread pool.
  await Task.Run(() => DoProcessing(progress));
  textBox1.Text = "Done!";
}

public void DoProcessing(IProgress<int> progress)
{
  for (int i = 0; i != 100; ++i)
  {
    Thread.Sleep(100); // CPU-bound work
    if (progress != null)
      progress.Report(i);
  }
}

了解更多關於進步記者在這里與異步/等待。

更新 -

以下是您在代碼中執行此操作以報告進度的方法。

使用progresschanged處理程序定義進度對象。 下面是一個帶有匿名處理程序的示例。

  IProgress<UploadStep> progress = new Progress<UploadStep>(step =>
  {
      // sample consumption of progress changed event.
      if (step.Complete)
      {
          // Do what ever you want at the end.
      }
      else
      {
          statusTxtBox.Text = step.Message;
      }
  }); 

使用此Progress對象調用DoUpload

 DoUpload(driveInfo, progress);

現在，在您的DoUpload方法中進行更改：

public void DoUpload(DriveInfo sel, IProgress<UploadStep> progress)
{
    // Check that there is a device selected
    if (sel != null)
    {
        progress.Report(new UploadStep { Message = "First Task..." });

        // Generate List of images to upload
        var files = Directory.EnumerateFiles(sel.Name, "*.*", SearchOption.AllDirectories)
            .Where(s => s.EndsWith(".jpeg") || s.EndsWith(".jpg") || s.EndsWith(".png"));

        if (files.Count() > 0)
        {
            // Manage each image
            foreach (string item in files)
            {
                // Generate thumbnail byte array
                Thumbnails.Add(new ByteImage { Image = GenerateThumbnailBinary(item) });
            }

            progress.Report(new UploadStep { Message = "Generated Thumnails..." });

            foreach (string item in files)
            {
                // Generate new name
                Filenames.Add(
                    new NFile
                    {
                        OldName = Path.GetFileNameWithoutExtension(item),
                        NewName = Common.Security.KeyGenerator.GetUniqueKey(32)
                    });
            }

            progress.Report(new UploadStep { Message = "Uplaoding to database..." });
        }
    }
}

Answer 2

我將創建一個單獨的Thread並將列表和Dispatcher傳遞給它。 每次項目准備就緒時，您應該Invoke Dispatcher並設置結果。

var list<UploadStep> items = new List<UploadStep>();

// queue workitems
var currentDispatcher = Dispatcher.CurrentDispatcher;
var thread = new Thread(() =>
    {
        foreach(var item in items)
        {
            // do you thing with downloading..

            currentDispatcher.Invoke(() =>
            {
                // Add to observable class or other gui items..
            });
        }
    });

thread.Start(); 

---

如果您想使用任務庫進行操作，則應等待每個項目。

var list<UploadStep> items = new List<UploadStep>();

foreach(var step in items)
{
    var myResults = await DoYourDownload(step);
    // Change some gui stuff.
}

---

所有這些項目將連續處理。

這是一篇關於如何並行處理它們的文章： 在foreach循環中啟動任務使用最后一項的值