ListView not updating after ObservableCollection changed

Question

I have been trying for some hours to get my ListView with ObservableCollection to work. However, no luck. I also read through some posts in here and there and try to match and still no good. Please give me pointer on where it went wrong.

Basically, what I am trying to do is split logic from VM to Helper class. And the logic in this class will update the data but VM does not aware of it.

My problem is in copying file function, the job status does not change the view data. I tried Messenger.Default.Send (from the helper) and Messenger register (in VM), to accept the changes, still no luck.

I am using MVVM Light, WPF, C# by the way.

Here is my code for Model.

public class MyFile : ViewModelBase
{
    public string fullFileName { get; set; }
    public string fileName { get; set; }


    private string _jobStatus;
    public string jobStatus
    {
        get { return _jobStatus; }
        set { Set(ref _jobStatus, value); }
    }
}

Here is my code for Helper.

class FileHelper
{
    public List GetFileName(string dir)
    {
        List lstFiles = new List();

        foreach (var file in (new DirectoryInfo(dir).GetFiles()))
        {
            if (file.Name.ToLower().Contains("xls") && !file.Name.Contains("~$"))
                lstFiles.Add(new MyFile() { fullFileName = file.FullName, fileName = file.Name, jobStatus = "-" });
        }

        return lstFiles;
    }

    public bool CopyFiles(string destDir, List lstFiles)
    {
        try
        {
            int counter = 0;

            foreach (MyFile f in lstFiles)
            {
                f.jobStatus = "Copying";
                File.Copy(f.fullFileName, Path.Combine(destDir, f.fileName),true);
                f.jobStatus = "Finished";
                counter += 1;
                Console.WriteLine("M: " + DateTime.Now.ToString("hh:mm:ss") + "    " + counter);
                Messenger.Default.Send(counter, "MODEL");
            }

            return true;
        }
        catch (Exception e)
        {
            Console.WriteLine("Error: " + e.Message);
            return false;
        }
    }
}

Here is my code for VM.

public class MainViewModel : ViewModelBase
{
    public ICommand CmdJob { get; private set; }



    private ObservableCollection fileList;
    public ObservableCollection FileList
    {
        get { return fileList; }
        set { Set(ref fileList, value); }
    }


    private string counter;
    public string Counter
    {
        get { return counter; }
        set { Set(ref counter, value); }
    }


    public MainViewModel()
    {
        Messenger.Default.Register(this, "MODEL", UpdateCounter);

        CmdJob = new RelayCommand

mm8 · Accepted Answer

You cannot both update the UI and copy files on the same thread simultaneously.

You should either perform the copy on a background thread or use an asynchronous API, e.g.:

public async Task CopyFiles(string destDir, List lstFiles)
{
    try
    {
        int counter = 0;

        foreach (MyFile f in lstFiles)
        {
            f.jobStatus = "Copying";
            using (Stream source = File.Open(f.fullFileName))
            using (Stream destination = System.IO.File.Create(Path.Combine(destDir, f.fileName)))
                await source.CopyToAsync(destination);
            f.jobStatus = "Finished";
            counter += 1;
            Console.WriteLine("M: " + DateTime.Now.ToString("hh:mm:ss") + "    " + counter);
            Messenger.Default.Send(counter, "MODEL");
        }

        return true;
    }
    catch (Exception e)
    {
        Console.WriteLine("Error: " + e.Message);
        return false;
    }
}

Note that you have to modify the signature of your method to be able to use the async/await keywords that were introduced in the .NET Framework 4.5 and C#5.

You should also await async methods "all the way":

private Task CopyFile()
{
    var fh = new FileHelper();
    if (await fh.CopyFiles(@"C:\Test\Destination\", fileList.ToList()))
        Messenger.Default.Send("Files copying finished", "VM");
    else
        Messenger.Default.Send("Files copying failed", "VM");
}

private async void Action_Job(object tag)
{
    if (tag == null || string.IsNullOrEmpty(tag.ToString()))
        return;

    switch (tag.ToString())
    {
        case "GET": GetFile();  break;
        case "COPY": await CopyFile(); break;
    }
}

ListView not updating after ObservableCollection changed

Answers (2)

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