在测试WPF项目中我试图使用TPL数据流来枚举给定父目录的所有子目录，并创建具有特定文件扩展名的文件列表，例如＆＃34; .XLSX＆＃34 ;.我使用2个块，第一个是dirToFilesBlock，最后是fileActionBlock。
要创建遍历所有子目录的递归效果，第一个块有一个链接返回自身，链接谓词测试以查看输出项是否是目录。这是我在一本关于异步编程的书中找到的方法。第二个链接是fileActionBlock，然后根据链接谓词测试将文件添加到列表中，以查看文件是否具有正确的扩展名。
我遇到的问题是在使用btnStart_Click开启之后，它永远不会完成。也就是说，我们永远不会在事件处理程序中低于await以显示“已完成”消息。我明白我可能需要调用dirToFilesBlock.Complete（），但我不知道代码应该在哪里以及在什么条件下？我不能在初始帖子之后调用它，因为它会停止从提供子目录返回链接。我已经尝试使用InputCount和OutputCount属性，但没有走得太远。我希望，如果可能的话，保持数据流的结构，因为这意味着我还可以通过链接返回每个新目录来更新UI，以便向用户提供一些进展反馈。
我对TPL数据流非常陌生，感谢任何帮助。
以下是代码隐藏文件中的代码：
public partial class MainWindow : Window
{
TransformManyBlock<string, string> dirToFilesBlock;
ActionBlock<string> fileActionBlock;
ObservableCollection<string> files;
CancellationTokenSource cts;
CancellationToken ct;
public MainWindow()
{
InitializeComponent();
files = new ObservableCollection<string>();
lst.DataContext = files;
cts = new CancellationTokenSource();
ct = cts.Token;
}
private Task Start(string path)
{
var uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
dirToFilesBlock = new TransformManyBlock<string, string>((Func<string, IEnumerable<string>>)(GetFileSystemItems), new ExecutionDataflowBlockOptions() { CancellationToken = ct });
fileActionBlock = new ActionBlock<string>((Action<string>)ProcessFile, new ExecutionDataflowBlockOptions() {CancellationToken = ct, TaskScheduler = uiScheduler});
// Order of LinkTo's important here!
dirToFilesBlock.LinkTo(dirToFilesBlock, new DataflowLinkOptions() { PropagateCompletion = true }, IsDirectory);
dirToFilesBlock.LinkTo(fileActionBlock, new DataflowLinkOptions() { PropagateCompletion = true }, IsRequiredDocType);
// Kick off the recursion.
dirToFilesBlock.Post(path);
return Task.WhenAll(dirToFilesBlock.Completion, fileActionBlock.Completion);
}
private bool IsDirectory(string path)
{
return Directory.Exists(path);
}
private bool IsRequiredDocType(string fileName)
{
return System.IO.Path.GetExtension(fileName) == ".xlsx";
}
private IEnumerable<string> GetFilesInDirectory(string path)
{
// Check for cancellation with each new dir.
ct.ThrowIfCancellationRequested();
// Check in case of Dir access problems
try
{
return Directory.EnumerateFileSystemEntries(path);
}
catch (Exception)
{
return Enumerable.Empty<string>();
}
}
private IEnumerable<string> GetFileSystemItems(string dir)
{
return GetFilesInDirectory(dir);
}
private void ProcessFile(string fileName)
{
ct.ThrowIfCancellationRequested();
files.Add(fileName);
}
private async void btnStart_Click(object sender, RoutedEventArgs e)
{
try
{
await Start(@"C:\");
// Never gets here!!!
MessageBox.Show("Completed");
}
catch (OperationCanceledException)
{
MessageBox.Show("Cancelled");
}
catch (Exception)
{
MessageBox.Show("Unknown err");
}
finally
{
}
}
private void btnCancel_Click(object sender, RoutedEventArgs e)
{
cts.Cancel();
}
}
}
答案 0 :(得分：2)
尽管这是一个老问题，但在数据流循环中处理完成仍然是一个问题。
在您的情况下，您可以让TransfomBlock保留仍在航班中的物品的数量。这表示该块正忙于处理任意数量的项目。然后，当块不忙并且它们的两个缓冲区都为空时，您只会调用Complete()。您可以在我撰写Finding Completion in a Complex Flow: Feedback Loops
public partial class MainWindow : Window {
TransformManyBlock<string, string> dirToFilesBlock;
ActionBlock<string> fileActionBlock;
ObservableCollection<string> files;
CancellationTokenSource cts;
CancellationToken ct;
public MainWindow() {
InitializeComponent();
files = new ObservableCollection<string>();
lst.DataContext = files;
cts = new CancellationTokenSource();
ct = cts.Token;
}
private async Task Start(string path) {
var uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
dirToFilesBlock = new TransformManyBlock<string, string>((Func<string, IEnumerable<string>>)(GetFileSystemItems), new ExecutionDataflowBlockOptions() { CancellationToken = ct });
fileActionBlock = new ActionBlock<string>((Action<string>)ProcessFile, new ExecutionDataflowBlockOptions() { CancellationToken = ct, TaskScheduler = uiScheduler });
// Order of LinkTo's important here!
dirToFilesBlock.LinkTo(dirToFilesBlock, new DataflowLinkOptions() { PropagateCompletion = true }, IsDirectory);
dirToFilesBlock.LinkTo(fileActionBlock, new DataflowLinkOptions() { PropagateCompletion = true }, IsRequiredDocType);
// Kick off the recursion.
dirToFilesBlock.Post(path);
await ProcessingIsComplete();
dirToFilesBlock.Complete();
await Task.WhenAll(dirToFilesBlock.Completion, fileActionBlock.Completion);
}
private async Task ProcessingIsComplete() {
while (!ct.IsCancellationRequested && DirectoryToFilesBlockIsIdle()) {
await Task.Delay(500);
}
}
private bool DirectoryToFilesBlockIsIdle() {
return dirToFilesBlock.InputCount == 0 &&
dirToFilesBlock.OutputCount == 0 &&
directoriesBeingProcessed <= 0;
}
private bool IsDirectory(string path) {
return Directory.Exists(path);
}
private bool IsRequiredDocType(string fileName) {
return System.IO.Path.GetExtension(fileName) == ".xlsx";
}
private int directoriesBeingProcessed = 0;
private IEnumerable<string> GetFilesInDirectory(string path) {
Interlocked.Increment(ref directoriesBeingProcessed)
// Check for cancellation with each new dir.
ct.ThrowIfCancellationRequested();
// Check in case of Dir access problems
try {
return Directory.EnumerateFileSystemEntries(path);
} catch (Exception) {
return Enumerable.Empty<string>();
} finally {
Interlocked.Decrement(ref directoriesBeingProcessed);
}
}
private IEnumerable<string> GetFileSystemItems(string dir) {
return GetFilesInDirectory(dir);
}
private void ProcessFile(string fileName) {
ct.ThrowIfCancellationRequested();
files.Add(fileName);
}
private async void btnStart_Click(object sender, RoutedEventArgs e) {
try {
await Start(@"C:\");
// Never gets here!!!
MessageBox.Show("Completed");
} catch (OperationCanceledException) {
MessageBox.Show("Cancelled");
} catch (Exception) {
MessageBox.Show("Unknown err");
} finally {
}
}
private void btnCancel_Click(object sender, RoutedEventArgs e) {
cts.Cancel();
}
}