C# backgroundworker issue

Question

I am having an issue with backgroundworker in c#. I am coding a dll file.

This is my code in a Class Library (.NET Framework) type project within VS 2019:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace States
{    
    public class ST
    {        
        public static void Read()
        {
            BackgroundWorker bgwMessage = new BackgroundWorker();
            bgwMessage.DoWork += new DoWorkEventHandler(BgwFileOpen_DoWork);
            bgwMessage.RunWorkerAsync();
        }
       
        private static void BgwFileOpen_DoWork(object sender, DoWorkEventArgs e)
        {
            MessageBox.Show("Ran");
        }
    }
}

When I call the Read() method using the Immediate window the command in background worker's DoWork method does not run. Debguging the problem line by line shows that the Read() method is running but it does not call RunworkerAsync somehow.

*Update1: starting a thread also did not work either:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TradeStates
{
    
    public class ST
    {
        
        public static void Read()
        {
            Thread thr = new Thread(new ThreadStart(MSGshow));
            thr.Start();
        }
        public static void MSGshow()
        {
            MessageBox.Show("Ran");
        }


    }
}

As the BackgroundWorker class is IDisposable, consider moving its declaration into a field, which you then dispose of later, after the worker has finished. — Julius, Apr 02 '21 at 14:10
Hmm, "the Immediate window." Was the immediate window always capable of showing message boxes? Assuming that you are executing the command in the Immediate window while debugging is in progress, try replacing "MessageBox.Show("Ran")" with "Debug.WriteLine("Ran")" and see if the output shows up in the Debug category of the Output window. — Julius, Apr 02 '21 at 14:13
@Julius if i put the messagebox in "Read" method, it will be executed. i tried "Debug.WriteLine" it is not executed either. — RDS, Apr 02 '21 at 14:21

Kit · Answer 1 · 2021-04-02T15:59:32.517

A few things...

Correctly Implementing a Background Worker

The DoWork event is fired once to do the background work and must not do anything that accesses UI controls/UI thread.

There are two other events that you can use. ProgressChanged is used to report progress. For example, you could implement that method to update a progress bar. The other one, and the one I think you should be interested in is RunWorkerCompleted. In your case you'd have something like

bgwMessage.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(BgwFileOpen_ShowDialog);
...
private void BgwFileOpen_ShowDialog(object sender, RunWorkerCompletedEventArgs e)
{
    MessageBox.Show("Ran");
}

Some other thoughts

Your background worker should usually be a property of a Form or other winforms class as BackgroundWorker inherits from Component.
When the parent of the background worker is disposed, it should call the Dispose() on the background worker.

The BackgroundWorker Class documentation provides a great example of how to use the class properly.

Using a Thread or Task Instead

If you must create and start the worker from Read(), I suggest that you instead start a Thread instead, and have it send a message to the UI thread when done. Your message handler would then fire up the message box.

You can even use a Task, and then add a continuation to the task that continues on the UI thread, calling MessageBox.Show().

Immediate Window Issues

It appears that the Immmediate window may have issues executing threads or at least showing the outputs/results of other threads other than the one in which it is running. It's designed for interacting with you (the developer) more so than as a fully functional environment to run applications in, such as winforms.

I am confident that if you design your Read() method to accept a background worker that is properly implemented (i.e. created and setup outside of Read()), and then call RunWorkerAsync() inside Read(), the message box should pop up as expected -- just not that you'd see it when going via Immediate window.

thank you for your reply at the first stage. I also tried the "Thread" approach. but it also did not run either. I edited the original question and included my second try. — RDS, Apr 02 '21 at 15:31
Just like with the BackgroundWorker, you cannot call MessageBox.Show() in a non-UI thread. — Kit, Apr 02 '21 at 15:41
Maybe an exception is being thrown, and somehow the Immediate window is not capturing/showing the exception... have you tried running your code normally to see if it executes properly? If it does, I wouldn't even be concerned about it not showing up in the Immediate window. — Kit, Apr 02 '21 at 15:44

score 1 · Accepted Answer · answered Apr 02 '21 at 15:49

I would suggest using Tasks. It works with any dotnet above 4.5 (4.0 also with additional packages)

using System.Threading.Tasks;
public class ST
{        
    public static async Task Read()
    {
        await Task.Run(() => {
              //Do some big work here
        };
    }               
}

Then for example on your button click event just call:

private async void Button_Click(object sender, EventArgs e)
{
   await ST.Read();
   MessageBox.Show("Ran");
}

This will not freeze your view while you do that big Read task and will come back to the next line of the Button_Click function once it's done to show the dialog result.
You can even add some code before the Read call to warn the user that something is happening in the background :)

C# backgroundworker issue

2 Answers2

Correctly Implementing a Background Worker

Using a Thread or Task Instead

Immediate Window Issues