Question

I’m writing a class that performs a certain operation in a library. But the operation is tedious, and I want to be able to find out the progress of the method inside that class so that I can use it in a WinForms application to report the progress.

I’m planning to run my class on another thread in my WinForms application and I want the class to be separated from the concerns of the WinForms application, and I don’t want to bind it to anything specific other than what it does.

What would be the best way to implement a progress reporting mechanism in a library class?

Would it be a good idea to somehow have a progress variable in the class, and add an event listener to it in my WinForms application? And if it is, how can I do it?

Edit: I have used the BackgroundWorker class before, but my problem is I don’t want my library class to be concerned with any of the multithreading operations. So I don’t want to invoke ReportProgress in the library class, I want to (maybe) have a variable in the class that contains the current progress and I want the UI thread to somehow “subscribe” to it. I don’t know if that’s a good way to design it though.

Answer 1

Look into the BackgroundWorker class. It supports automatic marshaling across threads for progress reporting, and it has a very simple event model for this kind of support.

Edit: Given your position on using BackgroundWorker directly, what you might do is create a simple wrapper:

// Error checking elided for expository purposes.
public interface IProgressReporter 
{
    void ReportProgress(int progress, object status);
}

public class BackgroundWorkerProgressReporter : IProgressReporter
{
    private BackgroundWorker _worker;
    public BackgroundWorkerProgressReporter(BackgroundWorker worker)
    {
        _worker = worker;
    }

    public void ReportProgress(int progress, object status)
    {
        _worker.ReportProgress(progress, status);
    }
}

Then, alter the constructor (or add a property) of the class that you want to report progress to accept an IProgressReporter. This is a form of dependency injection, and should meaningfully allow your object to report progress whilst also avoiding specific dependencies on threading libraries.