WPF, PRISM and EventAggregrator

Question

I'm having some trouble with using EventAggregator within my application. The issue I am facing is that the UI will not update until the current processing has stopped. I was under the impression that EventAggregator ran in its own thread and therefore should be able to update the UI as soon as an event is published. Have I misunderstood this concept?

below is my code

Bootstrapper.cs

class Bootstraper : UnityBootstrapper
{
    protected override DependencyObject CreateShell()
    {
        return ServiceLocator.Current.GetInstance();
    }

    protected override void InitializeShell()
    {
        Application.Current.MainWindow.Show();
    }
}

App.xmal.cs

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        var bs = new Bootstraper();
        bs.Run();
    }
}

MainWindow.xmal

ProcessLogView.xaml

ProcessLogViewModel.cs

class ProcessLogViewModel: EventsBase
{

    private ObservableCollection logMessage;

    public ObservableCollection LogMessage
    {
        get { return logMessage; }
        set { SetProperty(ref logMessage, value); }
    }

    public ProcessLogViewModel()
    {
        //If statement is required for viewing the MainWindow in design mode otherwise errors are thrown
        //as the ProcessLogViewModel has parameters which only resolve at runtime. I.E. events
        if (!(bool)DesignerProperties.IsInDesignModeProperty.GetMetadata(typeof(DependencyObject)).DefaultValue)
        {
            events.GetEvent().Subscribe(UpdateProgressLog);
            LogMessage = new ObservableCollection();
        }
    }

    public void HyperLinkClicked(object sender, RequestNavigateEventArgs e)
    {
        System.Diagnostics.Process.Start(e.Uri.AbsoluteUri);
    }

    private void UpdateProgressLog(LogPayload msg)
    {
        LogMessage.Add(msg);
    }
}

EventsBase.cs

public class EventsBase: BindableBase
{
    public static IServiceLocator svc = ServiceLocator.Current;
    public static IEventAggregator events = svc.GetInstance();
}

LogEvents.cs

public class LogUpdate : PubSubEvent { }

public class LogEvents : EventsBase
{
    public static void UpdateProcessLogUI(LogPayload msg)
    {
        events.GetEvent().Publish(msg);
    }
}

LogEvent struct

public struct LogPayload
{
    public string Message { get; set; }
    public int LinkNum { get; set; }
    public string Link { get; set; }
    public string SecondLink { get; set; }
}

Then if I drag and drop a spreadsheet on to the ProcessInputView the following code is hit within my ProcessInputViewModel.cs

    public void FileDropped(object sender, DragEventArgs e)
    {
        string[] files;
        string[] cols;
        TextBox txtFileName = (TextBox)sender;
        SpreadsheetCheck result = new SpreadsheetCheck();
        DDQEnums.TranTypes tranType;
        List fileFormats = new List();

        fileFormats.Add(Constants.FileFormats.XLS);
        fileFormats.Add(Constants.FileFormats.XLSX);

        if (e.Data.GetDataPresent(DataFormats.FileDrop, true))
        {
            files = e.Data.GetData(DataFormats.FileDrop, true) as string[];

            if (files.GetLength(0) > 1)
            {
                result.IsValid = false;
                result.Message = "Only drop one file per input box";
            }
            else
            {
                result = Utils.CheckIfSpreadsheetIsValidForInput(files[0], fileFormats, (DDQEnums.TranTypes)txtFileName.Tag, out tranType);

                LogEvents.UpdateProcessLogUI(Utils.BuildLogPayload(string.Format("Checking {0} Spreadsheet Column Format", tranType)));
                if (result.IsValid)
                {
                    cols = Utils.GetSpreadsheetColumns(tranType);
                    if (cols.GetLength(0) > 0)
                    {
                        result = CheckSpreadsheetColumnFormat(files[0], cols, tranType);
                        txtFileName.Text = Path.GetFileName(files[0]);
                    }
                    else
                    {
                        result.IsValid = false;
                        result.Message = "Unable to get column definations to be used";
                    }
                }
            }
            IsInputValid = result.IsValid;
            LogEvents.UpdateProcessLogUI(Utils.BuildLogPayload(result.Message));
            ProcessInputViewEventsPublish.SendInputValidStatus(IsInputValid, SelectedProcess, files[0]);
        }
        else
        {
            LogEvents.UpdateProcessLogUI(Utils.BuildLogPayload("Unable to get the file path for the dropped file"));
        }
    }

This all works fine except the ProcessLog listview is not updated until the FileDropped method has completed. This can been seen clearer by adding a thread.sleep into the FileDropped method just after the LogEvents.UpdateProcessLogUI method.

Have I implemented this incorrectly and if so how do I get real time updates in the ProcessLogView listview while using IEventAggregator?

gheff · Accepted Answer

OK, so turns out I was being pretty stupid. The FilesDropped method within my ProcessInputViewModel was running on the UI thread so of course the UI didn't update until after processing had finished.

I solved this by creating a new method FileDroppedBackground and running this on a new thread.

FileDropped method

    public void FileDropped(object sender, DragEventArgs e)
    {
        TextBox txtFileName = (TextBox)sender;
        DDQEnums.TranTypes tag = (DDQEnums.TranTypes)txtFileName.Tag;
        string fileName = string.Empty;

        new Thread(() => fileName = FileDroppedBackground(tag, e)).Start();
        txtFileName.Text = fileName;
    }

FileDroppedBackground method

    private string FileDroppedBackground(DDQEnums.TranTypes tag, DragEventArgs e)
    {
        string[] files;
        string[] cols;

        string returnValue = string.Empty;


        SpreadsheetCheck result = new SpreadsheetCheck();
        DDQEnums.TranTypes tranType;
        List fileFormats = new List();

        fileFormats.Add(Constants.FileFormats.XLS);
        fileFormats.Add(Constants.FileFormats.XLSX);

        if (e.Data.GetDataPresent(DataFormats.FileDrop, true))
        {
            files = e.Data.GetData(DataFormats.FileDrop, true) as string[];

            if (files.GetLength(0) > 1)
            {
                result.IsValid = false;
                result.Message = "Only drop one file per input box";
            }
            else
            {
                result = Utils.CheckIfSpreadsheetIsValidForInput(files[0], fileFormats, tag, out tranType);

                LogEvents.UpdateProcessLogUI(Utils.BuildLogPayload(string.Format("Checking {0} Spreadsheet Column Format", tranType)));
                Thread.Sleep(10000);

                if (result.IsValid)
                {
                    cols = Utils.GetSpreadsheetColumns(tranType);
                    if (cols.GetLength(0) > 0)
                    {
                        result = CheckSpreadsheetColumnFormat(files[0], cols, tranType);
                        returnValue = Path.GetFileName(files[0]);
                    }
                    else
                    {
                        result.IsValid = false;
                        result.Message = "Unable to get column definations to be used";
                    }
                }
            }
            IsInputValid = result.IsValid;
            LogEvents.UpdateProcessLogUI(Utils.BuildLogPayload(result.Message));
            ProcessInputViewEventsPublish.SendInputValidStatus(IsInputValid, SelectedProcess, files[0]);
        }
        else
        {
            LogEvents.UpdateProcessLogUI(Utils.BuildLogPayload("Unable to get the file path for the dropped file"));
        }

        return returnValue;
    }

This then caused an exception within the UpdateProgressLog method in my ProcessLogViewModel about the ObservableCollection not being able to be updated from another thread

so I updated this method as follows

    private void UpdateProgressLog(LogPayload msg)
    {
        dispatcher.Invoke(new Action(() => { LogMessage.Add(msg); }));
    }

I defined dispatcher as Dispatcher dispatcher = Dispatcher.CurrentDispatcher; at the top of my class.

Now when I run the application and drop a spreadsheet on to the ProcessInputView the log is updated in real-time and not when the method finishes processing

WPF, PRISM and EventAggregrator

Answers (2)

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