FileSystemWatcher and GUI

问题

I have a little problem with my WPF project and the FileSystemWatcher class. In my MainWindow class the watcher begins to watch a folder when Button Start is clicked in the UI. Everything works without any problems - the watcher recognizes correctly when a file is created. But while watcher is waiting it is not possible for user to do anything in the UI. It should be possible for nexample to click Stop...

 private void Start_Click(object sender, RoutedEventArgs e)
    {
        rdbTextBox.Document.Blocks.Clear();
        Start.IsEnabled = false;
        rdbTextBox.Document.Blocks.Add(new Paragraph(new Run("Test gestarte-Warte auf Befund....")));
        Stop.IsEnabled = true;

        watcher = new FileSystemWatcher(ConfigSettings.Default.FilePath); 

        // Only watch text files.
        // watcher.Filter = "*.bef";
        watcher.Filter = "*.txt";
        // Add event handlers.          
        watcher.Created += OnCreated;
        // Begin watching.
        watcher.EnableRaisingEvents = true;

        // Wait until new file in folder
        watcher.WaitForChanged(System.IO.WatcherChangeTypes.Created);           
        watcher.Dispose();

        // Parse letter
        edifactLetter = parser.ParseDocument(ConfigSettings.Default.FilePath + "\\" + fileName);
        // Validate Letter
        edifactVal.Validate(edifactLetter);

        writeResults();
        Start.IsEnabled = true;           
    }

    private void OnCreated(object sender, FileSystemEventArgs e)
    {   
        FileInfo file = new FileInfo(e.FullPath);
        fileName = file.Name;
    }

Can anyone explain me what I am doing wrong? Thanks!

回答1:

This is because WaitForChanged() is not an asynchronous method, it is synchronous. Meaning if you are using that in your UI thread it will get blocked.

See here: https://msdn.microsoft.com/en-us/library/67220zhk(v=vs.110).aspx

I suggest that you could create an event handler for the OnChanged event and then do what you need to do.

回答2:

Yes, WaitForChanged is a synchronous method:

This method waits indefinitely until the first change occurs and then returns.

You're calling that from the UI thread - therefore blocking any other UI thread interaction in the meantime. You don't want to do that.

You should probably just listen for the appropriate events - calling your parsing/validation methods in the event handler. You should also make sure you do all UI work in the UI thread, but ideally as little other work as possible... so unless the parsing and validation needs to interact with the UI, do it in a different thread.

回答3:

You can mark method async and put long running task into a task. Don't forget prevent another call while first one is running:

private async void Start_Click(object sender, RoutedEventArgs e)
{
    var button = (Button)sender;
    button.Enabled = false;
    await Task.Run(() =>
    {
        .. long running task here will not block UI
    });
    button.Enabled = true;
}

来源：https://stackoverflow.com/questions/31783356/filesystemwatcher-and-gui

标签

wpf

filesystemwatcher