Background worker - report progress with string array

Question

I need to return multiple STRING values from my backgroundworker in each loop, so I tried to use ReportProgress second parameter as string array. Example of code:

Answer 1

when you instanciate your BackgroundWorker, you'll have to set reportprogress to true:

worker = new BackgroundWorker { WorkerReportsProgress = true };

On the do work method you'll just need this:

 worker.ReportProgress(10, "Message");

Then something like this to catch the progress:

private void WorkerProgressChanged(object sender, ProgressChangedEventArgs e) {
            if (e.UserState != null) {
                MessageBox.Show(e.UserState);
            }
        }

Answer 2

I've solved a similar issue by adding a new ProgressChanged event listener to your background worker and block passing to the next loop if ProgressChanged not fired:

bool progressed;

backgroundWorker1.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
string[] workerResult = new string[2];
for (int i = 0; i < 2; ++i) {
    progressed=true;

    workerResult[0] = "this string";
    workerResult[1] = "some other string";
    backgroundWorker1.ReportProgress(i, workerResult);
    while (progressed)
    {
       //you can add a thread sleep 
    }
}


void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
     progressed = false;
}

Answer 3

Your code snippet is incapable of reproducing the problem. A standard mistake is to call ReportProgress() and then to continue modifying the object. It takes a while for the event handler to run, it will see the modified object, not the original. You avoid this by simply creating a new object so that the event handler always works with the original. Like this:

        //do some heavy calculating
        for (int i = 0; i < 2; ++i) {
            string[] workerResult = new string[2];
            workerResult[0] = "this string";
            workerResult[1] = "some other string";
            backgroundWorker1.ReportProgress(i, workerResult);
        }

Note how the array creation statement is moved inside the loop.