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Console progress bar. Code is under the MIT License:
using System;
using System.Threading;
static class Program {
static void Main() {
Console.Write("Performing some task... ");
using (var progress = new ProgressBar()) {
for (int i = 0; i <= 100; i++) {
progress.Report((double) i / 100);
using System;
using System.Text;
using System.Threading;
/// <summary>
/// An ASCII progress bar
/// </summary>
public class ProgressBar : IDisposable, IProgress<double> {
private const int blockCount = 10;
private readonly TimeSpan animationInterval = TimeSpan.FromSeconds(1.0 / 8);
private const string animation = @"|/-\";
private readonly Timer timer;
private double currentProgress = 0;
private string currentText = string.Empty;
private bool disposed = false;
private int animationIndex = 0;
public ProgressBar() {
timer = new Timer(TimerHandler);
// A progress bar is only for temporary display in a console window.
// If the console output is redirected to a file, draw nothing.
// Otherwise, we'll end up with a lot of garbage in the target file.
if (!Console.IsOutputRedirected) {
public void Report(double value) {
// Make sure value is in [0..1] range
value = Math.Max(0, Math.Min(1, value));
Interlocked.Exchange(ref currentProgress, value);
private void TimerHandler(object state) {
lock (timer) {
if (disposed) return;
int progressBlockCount = (int) (currentProgress * blockCount);
int percent = (int) (currentProgress * 100);
string text = string.Format("[{0}{1}] {2,3}% {3}",
new string('#', progressBlockCount), new string('-', blockCount - progressBlockCount),
animation[animationIndex++ % animation.Length]);
private void UpdateText(string text) {
// Get length of common portion
int commonPrefixLength = 0;
int commonLength = Math.Min(currentText.Length, text.Length);
while (commonPrefixLength < commonLength && text[commonPrefixLength] == currentText[commonPrefixLength]) {
// Backtrack to the first differing character
StringBuilder outputBuilder = new StringBuilder();
outputBuilder.Append('\b', currentText.Length - commonPrefixLength);
// Output new suffix
// If the new text is shorter than the old one: delete overlapping characters
int overlapCount = currentText.Length - text.Length;
if (overlapCount > 0) {
outputBuilder.Append(' ', overlapCount);
outputBuilder.Append('\b', overlapCount);
currentText = text;
private void ResetTimer() {
timer.Change(animationInterval, TimeSpan.FromMilliseconds(-1));
public void Dispose() {
lock (timer) {
disposed = true;
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mbodm commented May 7, 2022

@Leendert-JanFloor In a typical modern approach, you are using the TAP pattern. You are also using the HttpClient class more often today, than the WebClient class (but this is not the main topic here).

One of the advantages in a TAP pattern approach is: The user of your library can decide on his own, how and where the progress-handling happens. Example given:

  • Is it spooled onto the UI thread ?
  • Is it spooled onto a threadpool thread ?
  • Etc.

This solves some downsides, your mentioned older callback approach has. Your mentioned approach is called the EAP pattern. Just use your Google Fu techniques, to understand the differences and why EAP is used in the earlier years and TAP is more widely used today.

Besides the differences, the TAP pattern approach is developed together with the uprising of async/await and fits very well into it. Or better said: The TAP pattern approach exists specifically cause of async/await driven scenarios. Which are not that rare today.

Good sources, for all of above stuff, are posts containing 1 of these 2 names:

  • Stephen Toub
  • Stephen Cleary

These 2 guys knew exactly what they are talking about and offer great resources on that topic. The former one is an oustanding developer at MS and has developed most of the .NET threading and async/await stuff. The latter one has a lot of experience in asynchronous .NET programming and has some great resources.

All that said:

The use of IProgress<> (and it´s Report() method) allows your TAP library users, to decide on their own, if the report "callback" is happening on the UI thread or not. Often, in WinForms or WPF scenarios, you want that. Because you can access Form controls (like Button, CheckBox, ProgressBar and so on) solely from the UI thread.

So, if you wanna access your Button directly in the "callback" report, that report has to run on the UI thread. But often you also not want that. Or you use some approach that risks to block your UI thread and you have to handle with a lot of stuff, to not block the UI thread. There is this good old problem of "i can´t move my application window while (in example) my download progress happens!". The TAP pattern and IProgress<> offers solutions for exactly that behaviours.

More on that topic just no longer fits this GitHub issue post. 😉 But at least above statements hopefully give you some starting point. I hope it helped at least a bit, to shed some light on that topic.

Have a nice day!

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This helped me a lot, thanks for sharing. Cheers.

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Wow, this is so nice!

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This was much appreciated! Thank you for sharing. :)

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