WPF MVVM Console Output to a TextBox within a View

Question

I am writing an application that updates files and then will eventually import the updated files to a database. I want to display a message about which file is being updated and when the process has finished. I want the message to come from the console because eventually the importer library I am using displays helpful messages through the console and I will want to display those too. I was able to do this before in a WPF app, but all of my code was in the code behind of the view, and I want to keep the MVVM pattern and separate the code into a ViewModel. My problem is I do not know how to get a reference to my TextBox that is in my View. Once I am able to get a hold of the TextBox in my ViewModel I will be able to send the Console Writes to the TextBox.

Here is my View

Here is the ViewModel

using DICOM_Importer.Commands;
using DICOM_Importer.Views;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Input;

namespace DICOM_Importer.ViewModels
{
    public class StudyImporterViewModel : INotifyPropertyChanged, IDataErrorInfo
    {
        private string importerTitle;
        private string importerPath;
        public DirectoryInfo[] directories;
        GetIndividualSubjectDirectories subjectDirectories = new GetIndividualSubjectDirectories();
        ConsoleOutputStream outputter;

        /// 
        /// Gets the study information from the HomeView
        /// 
        public String ImporterTitle
        {
            get { return importerTitle; }
            set
            {
                importerTitle = value;
                OnPropertyChanged("ImporterTitle");
            }
        }

        public String ImporterPath
        {
            get { return importerPath; }
            set
            {
                importerPath = value;
                OnPropertyChanged("ImporterPath");
            }
        }


        public StudyImporterViewModel()
        {
            ImportCommand = new ActivateImport(this);
            outputter = new ConsoleOutputStream(ImportConsole); //Here is where the error is
            Console.SetOut(outputter);
        }

        public ICommand ImportCommand
        {
            get;
            private set;
        }

        public void Import()
        {
            MessageBoxResult result = MessageBox.Show("This will import every series in the Import Directory. Are you sure you want to Import?", "Import Confirmation", MessageBoxButton.OKCancel);


            switch (result)
            {
                case MessageBoxResult.OK:
                    if(importerTitle == "SPIROMICS2")
                    {
                        Console.WriteLine("Importing SPIROMICS2 Scans to Mifar");
                        directories = subjectDirectories.GetSubjectDirectories(importerPath);
                        subjectDirectories.GetSeriesDirectories(directories);
                        Console.WriteLine("Import Complete");

                    }
                    else if(importerTitle == "BLF")
                    {
                        Console.WriteLine("BLF");
                    }
                    else if(importerTitle == "PRECISE")
                    {
                        Console.WriteLine("PRECISE");
                    }

                    break;
                case MessageBoxResult.Cancel:
                    MessageBox.Show("CANCEL", "Nope!");
                    break;
            }
        }

        #region Error Model
        public string Error
        {
            get;
            set;
        }
        #endregion

        #region Error Definition
        public string this[string columnName]
        {
            get 
            {
                if (columnName == "ImporterTitle")
                {
                    if (String.IsNullOrWhiteSpace(ImporterPath))
                    {
                        Error = "There is no selected study to import";
                    }
                    else 
                    {
                        Error = null;
                    }
                }
                return Error;
            }
        }
        #endregion

        #region PropertyChangedEventHandler
        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        #endregion


    }
}

Here is my ConsoleOutputStream Command

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Controls;

namespace DICOM_Importer.Commands
{
    class ConsoleOutputStream : TextWriter
    {
        TextBox textBox = null;


        public ConsoleOutputStream(TextBox ouput)
        {
            textBox = ouput;
        }

        public override void Write(char value)
        {
            base.Write(value);
            textBox.Dispatcher.BeginInvoke(new Action(() => {
                textBox.AppendText(value.ToString());
            }));
        }

        public override Encoding Encoding
        {
            get { return System.Text.Encoding.UTF8; }
        }
    }
}

and here is the command for the button that will kick off all the file changes and imports

using DICOM_Importer.ViewModels;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace DICOM_Importer.Commands
{
    /// 
    /// Starts the import processes on a button click if there is a study available 
    /// 
    class ActivateImport : ICommand
    {

        private StudyImporterViewModel _studyImporterViewModel;

        public ActivateImport(StudyImporterViewModel viewModel)
        {
            _studyImporterViewModel = viewModel;
        }



        public event EventHandler CanExecuteChanged
        {
            //this is forcing the CommandManager to check the ICommand again. If we didn't have this then the buitton wouldl only be 
            //disabled if the window was loaded with a blank name, not if it was loaded with a name and then was deleted by the user
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public bool CanExecute(object parameter)
        {
            return String.IsNullOrWhiteSpace(_studyImporterViewModel.Error);
        }

        public void Execute(object parameter)
        {
            _studyImporterViewModel.Import();
        }
    }
}

Any help would be much appreciated!

sephiroth · Accepted Answer

You can redirect the Console output to a StringWriter and then write its content into the string you bound to the textbox every time a new console output is made.

ViewModel

private StringWriter _sw;
public string ConsoleOut { /* getter and setter */ }

// inside constructor
_sw = new StringWriter();
Console.SetOut(sw);
Console.SetError(sw);

xaml

The problem here is that every time you want to display the console output in the TextBlock you need to update the value of S with S = _sw.ToString();

Solution

I found this answer with the implementation of an enhanced StringWriter class that fires an event every time there is a write. With this, you only need to make a simple update:

ViewModel

private StringWriterExt _sw;
public string ConsoleOut { /* getter and setter */ }

// inside constructor
_sw = new StringWriterExt(true);
Console.SetOut(sw);
Console.SetError(sw);
_sw.Flushed += (s, a) => ConsoleOut = _sw.ToString();

WPF MVVM Console Output to a TextBox within a View

Answers (1)

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