Running a WPF Progress bar as a background worker thread

How to run a WPF progress bar as a background worker thread.

This code uses ICommand to respond to the user’s request to both and pause start the progress bar background process.

Step 1: Create a new WPF application

progressthread1

Step 2: Create the MainWindow.xaml user interface components

<Window x:Class="ProgressThread.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ProgressThread"
        mc:Ignorable="d"
        Title="MainWindow" 
        Height="250" Width="525">


    <Window.DataContext>
        <local:MainWindowViewModel/>
    </Window.DataContext>

    <Grid >
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>


        <ProgressBar 
            Value="{Binding CurrentProgress, Mode=OneWay}" 
            Visibility="Visible"
            VerticalAlignment="Center"
            Grid.Row="0"
            Height="60" Width="300"
            Minimum="0" Maximum="100" 
            Name="pbStatus" />

        <Button
            Grid.Row="1"
            Width="150" Height="50"
            Command="{Binding Command}"
            Content="{Binding ButtonLabel}"/>
    </Grid>
    
</Window>

Step 3: Create the ViewModel classes

BaseViewModel.cs

using System;
using System.ComponentModel;
using System.Diagnostics;

namespace ProgressThread
{
    public abstract class BaseViewModel : INotifyPropertyChanged
    {
        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion

        protected void OnPropertyChanged(string propertyName)
        {
            VerifyPropertyName(propertyName);
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        protected void OnPropertyChanged(int propertyValue)
        {
            VerifyPropertyName(propertyValue);
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyValue.ToString()));
            }
        }

        [Conditional("DEBUG")]
        private void VerifyPropertyName(string propertyName)
        {
            if (TypeDescriptor.GetProperties(this)[propertyName] == null)
                throw new ArgumentNullException(GetType().Name + " does not contain property: " + propertyName);
        }

        [Conditional("DEBUG")]
        private void VerifyPropertyName(int propertyValue)
        {
            if (TypeDescriptor.GetProperties(this)[propertyValue] == null)
                throw new ArgumentNullException(GetType().Name + " does not contain property: " + propertyValue.ToString());
        }
    }
}

MainWindowViewModel.cs

using System.ComponentModel;
using System.Threading;
using System.Windows;
using System.Windows.Input;

namespace ProgressThread
{
    public class MainWindowViewModel : BaseViewModel
    {
        private static bool _isRunning;
        private string _buttonLabel;
        private int currentProgress;
        private ICommand _command;
        private BackgroundWorker worker = new BackgroundWorker();

        public MainWindowViewModel()
        {
            worker.DoWork += DoWork;
            worker.ProgressChanged += ProgressChanged;
            worker.WorkerReportsProgress = true;
            worker.WorkerSupportsCancellation = true;
            CurrentProgress = 0;
            _isRunning = true;
            ButtonLabel = "GO";
        }

        private void ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            CurrentProgress = e.ProgressPercentage;
        }

        private void DoWork(object sender, DoWorkEventArgs e)
        {
            if (CurrentProgress >= 100)
            {
                CurrentProgress = 0;
            }

            while (CurrentProgress < 100 && !_isRunning)
            {
                worker.ReportProgress(CurrentProgress);
                Thread.Sleep(100);
                CurrentProgress++;
            }

            _isRunning = true;
        }

        public ICommand Command
        {
            get
            {
                return _command ?? (_command = new RelayCommand(x =>
                {
                    _isRunning = !_isRunning;

                    if (!_isRunning)
                    {
                        DoStuff();
                    }
                    else
                    {
                        ButtonLabel = "PAUSED";
                    }
                }));
            }
        }

        public int CurrentProgress
        {
            get { return currentProgress; }
            private set
            {
                if (currentProgress != value)
                {
                    currentProgress = value;
                    OnPropertyChanged("CurrentProgress");
                }
            }
        }

        public string ButtonLabel
        {
            get { return _buttonLabel; }
            private set
            {
                if (_buttonLabel != value)
                {
                    _buttonLabel = value;
                    OnPropertyChanged("ButtonLabel");
                }
            }
        }

        private void DoStuff()
        {
            ButtonLabel = "GO";
            worker.RunWorkerAsync();
        }
    }
}

Step 3: Add the event handling infratructure

EventArgs.cs

using System;

namespace ProgressThread
{
    public class EventArgs<T> : EventArgs
    {
        public EventArgs(T value)
        {
            Value = value;
        }

        public T Value { get; private set; }
    }
}

EventRaiser.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ProgressThread
{
    public static class EventRaiser
    {
        public static void Raise(this EventHandler handler, object sender)
        {
            if (handler != null)
            {
                handler(sender, EventArgs.Empty);
            }
        }

        public static void Raise<T>(this EventHandler<EventArgs<T>> handler, object sender, T value)
        {
            if (handler != null)
            {
                handler(sender, new EventArgs<T>(value));
            }
        }

        public static void Raise<T>(this EventHandler<T> handler, object sender, T value) where T : EventArgs
        {
            if (handler != null)
            {
                handler(sender, value);
            }
        }

        public static void Raise<T>(this EventHandler<EventArgs<T>> handler, object sender, EventArgs<T> value)
        {
            if (handler != null)
            {
                handler(sender, value);
            }
        }
    }
}

RelayCommand.cs

using System;
using System.Windows.Input;

namespace ProgressThread
{
    public class RelayCommand<T> : ICommand
    {
        private readonly Predicate<T> _canExecute;
        private readonly Action<T> _execute;

        public RelayCommand(Action<T> execute)
            : this(execute, null)
        {
            _execute = execute;
        }

        public RelayCommand(Action<T> execute, Predicate<T> canExecute)
        {
            if (execute == null)
            {
                throw new ArgumentNullException("execute");
            }
            _execute = execute;
            _canExecute = canExecute;
        }

        public bool CanExecute(object parameter)
        {
            return _canExecute == null || _canExecute((T)parameter);
        }

        public void Execute(object parameter)
        {
            _execute((T)parameter);
        }

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }
    }

    public class RelayCommand : ICommand
    {
        private readonly Predicate<object> _canExecute;
        private readonly Action<object> _execute;

        public RelayCommand(Action<object> execute)
            : this(execute, null)
        {
            _execute = execute;
        }

        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
            {
                throw new ArgumentNullException("execute");
            }
            _execute = execute;
            _canExecute = canExecute;
        }

        public bool CanExecute(object parameter)
        {
            return _canExecute == null || _canExecute(parameter);
        }

        public void Execute(object parameter)
        {
            _execute(parameter);
        }

        // Ensures WPF commanding infrastructure asks all RelayCommand objects whether their
        // associated views should be enabled whenever a command is invoked 
        public event EventHandler CanExecuteChanged
        {
            add
            {
                CommandManager.RequerySuggested += value;
                CanExecuteChangedInternal += value;
            }
            remove
            {
                CommandManager.RequerySuggested -= value;
                CanExecuteChangedInternal -= value;
            }
        }

        private event EventHandler CanExecuteChangedInternal;

        public void RaiseCanExecuteChanged()
        {
            CanExecuteChangedInternal.Raise(this);
        }
    }
}

So that when running we initially have the zero-progress as shown:

progressthread2

Clicking on the “GO” button initiates the progress bar thread as shown:

progressthread3

We can interrupt the progress by clicking on the “GO” button, which stops the background thread and switches the button label to “PAUSED”:

progressthread4


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