Accessing string in ViewModel from IValueConverter

Question

I am trying to create a converter that will take string property from ViewModel, compare it to time passed (time is inputted to TextBox HoursLimitProp in a format 07:30) and then change Label color accordingly. I know this is bad idea to do this way with

var SVM = new SettingsViewModel();

So what is the right way of accessing property in ViewModel from IValueConverter? I have tried to change SVM.HoursLimitProp to text as it is actually a value, but then I am getting null exception.

TimeExceededConverter.cs:

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Windows.Data;
using System.Windows.Media;

namespace Activitytracker
{
    class TimeExceededConverter : IValueConverter
    {
        #region IValueConverter Members

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            string text = (string)value;
            var dateNow = DateTime.Now;

            var SVM = new SettingsViewModel();

            List<int> TimeSplit = SVM.HoursLimitProp.Split(':').Where(x => int.TryParse(x, out _)).Select(int.Parse).ToList();

            DateTime RingTime = new DateTime(dateNow.Year, dateNow.Month, dateNow.Day, TimeSplit[0], TimeSplit[1], 00);

            TimeSpan res;
            var result = TimeSpan.TryParseExact(text, @"hh\:mm\:ss", CultureInfo.InvariantCulture, out res);

            if (res < RingTime.TimeOfDay)
            {
                return Brushes.Green;
            }

            return Brushes.Red;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Binding.DoNothing;
        }

        #endregion
    }
}

SettingsViewModel.cs:

....

    private string _hoursLimit;

    public string HoursLimitProp
    {
        get { return _hoursLimit; }
        set
        {
            if (_hoursLimit != value)
            {
                _hoursLimit = value;
                OnPropertyChanged();
            }
        }
    }

....

MainWindow.xaml:

...

                <Label DataContext="{Binding ViewModel}" Style="{StaticResource TopBarLabel_Style}" x:Name="lblTime" 
                   Content="{Binding Path=CurrentTime}" HorizontalAlignment="Left" Height="33" 
                   Foreground="{Binding Path=CurrentTime, Converter={StaticResource TimeExceededConverter}}"
                   Width="89" Grid.Column="1"/>
...

Answer 1

The TextBox can't invoke PropertyChanged because of the focus on it. I implement it with pressing the Return key after finishing the inputing. Below is my updated parts for your project:

Part 1: Add a MyCommand.cs in your ViewModel File.

class MyCommand : ICommand  
    {  
        private Func<object, bool> _canExecute;  
        private Action<object> _execute;  
  
        public event EventHandler CanExecuteChanged  
        {  
            add  
            {  
                if (_canExecute != null)  
                {  
                    CommandManager.RequerySuggested += value;  
                }  
            }  
            remove  
            {  
                if (_canExecute != null)  
                {  
                    CommandManager.RequerySuggested -= value;  
                }  
            }  
        }  
  
  
        public bool CanExecute(object parameter)  
        {  
            if (_canExecute == null) return true;  
            return _canExecute(parameter);  
        }  
  
        public void Execute(object parameter)  
        {  
            if (_execute != null && CanExecute(parameter))  
            {  
                _execute(parameter);  
            }  
        }  
  
        public MyCommand(Action<object> execute) : this(execute, null)  
        {  
        }  
        public MyCommand(Action<object> execute, Func<object, bool> canExecute)  
        {  
            _execute = execute;  
            _canExecute = canExecute;  
        }  
    }  

Part 2: Replace your HoursLimitBox TextBox with below code:

 <TextBox x:Name="HoursLimitBox" Text="{Binding HoursLimitProp,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Height="36" Margin="133,10,0,0"  VerticalAlignment="Top" Width="166" FontSize="20">  
            <TextBox.InputBindings>  
                <KeyBinding Command="{Binding EnterCommand}" Key="Return"></KeyBinding>  
            </TextBox.InputBindings>  
        </TextBox>  

Part 3: Add below code in ViewModel.cs

 private MyCommand _enterCommand;  
        public MyCommand EnterCommand  
        {  
            get  
            {  
                if (_enterCommand == null)  
                    _enterCommand = new MyCommand(new Action<object>  
                        (  
                        o =>  
                        {  
                            HoursLimitConfProp = HoursLimitProp;  
                        }  
                        ));  
                return _enterCommand;  
            }  
        }  

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Answer 2

I do some changes for your code to show the label.
Part 1 : Add a constructor in SettingsViewModel.cs to give value to

  public SettingsViewModel()  
        {  
            _currentTime = System.DateTime.Now.ToString("hh:mm:ss");  
            _hoursLimit = System.DateTime.Now.AddMinutes(10).ToString("hh: mm:ss");  
        }  

Part 2: The updated code for MainWindow.xaml

 <Window.Resources>  
        <local:TimeExceededConverter x:Key="TimeExceededConverter"></local:TimeExceededConverter>  
    </Window.Resources>  
    <Grid>  
        <Label x:Name="lblTime"  
               Content="{Binding Path=CurrentTime}"   
               Foreground="{Binding Path=CurrentTime, Converter={StaticResource TimeExceededConverter}}"  
               HorizontalAlignment="Left" Height="33"  Width="200">  
            <Label.DataContext>  
                <local:SettingsViewModel x:Name="ViewModel"></local:SettingsViewModel>  
            </Label.DataContext>  
        </Label>  
    </Grid>  

This is my answer based on my understanding, if I misunderstand, please point out.

---

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