是否可以按顺序启动后台工作人员？

Question

I want to use 3 background workers in sequential order.

First one should do a job, update UI and start the second background worker which does the same and then starts the last one. This should repeat only when a button is clicked again. Is such behavior possible to obtain?

public Form1()
{
     InitializeComponent();
     Bw1= = new BackgroundWorker();
     Bw2= = new BackgroundWorker();
     Bw3= = new BackgroundWorker();
     Bw1.DoWork += new DoWorkEventHandler(Bw1_DoWork);
     Bw1.ProgressChanged += new ProgressChangedEventHandler
                    (Bw1_ProgressChanged);
     Bw1.RunWorkerCompleted += new RunWorkerCompletedEventHandler
                    (Bw1_RunWorkerCompleted);
     Bw1.WorkerReportsProgress = true;
     Bw1.WorkerSupportsCancellation = true;
            ...
     Bw3.DoWork += new DoWorkEventHandler(Bw3_DoWork);
     Bw3.ProgressChanged += new ProgressChangedEventHandler
                    (Bw3_ProgressChanged);
     Bw3.RunWorkerCompleted += new RunWorkerCompletedEventHandler
                    (Bw3_RunWorkerCompleted);
     Bw3.WorkerReportsProgress = true;
     Bw3.WorkerSupportsCancellation = true;

}

private void btnStartAsyncOperation_Click(object sender, EventArgs e)
{

     btnStartAsyncOperation.Enabled = false;
     btnCancel.Enabled = true;
     // Kickoff the worker thread to begin its DoWork function.
     BW1.RunWorkerAsync();
}

//THE DO WORK PART
//UPDATE UI
//tHEN

void BW1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    STOP BW1;
    BW2.RUN();
}
        ...
    //Until BW 3 completes and here this should stop until next click

Answer 1

The reason for the background worker is not clear.

However, you could do the following (assuming there is no legitimate async IO work , and these tasks don't need to be run from a non threadpool thread ).

_{Note : If there was legitimate async IO work, you wouldn't need to wrap/offload to a Task and would just use await )}

The advantages are :

• It's sequential
• It factors simpler (less degrees of freedom)
• It's easier to read
• It uses the Async Await Pattern (and frees up the message pump / UI thread )
• And will work well with UI updates

Example

private async void btnStartAsyncOperation_Click(object sender, EventArgs e)
{

   try
   {

      await Task.Run(() => FirstTask1());

      // update the ui

      await Task.Run(() => FirstTask2());

      // update the ui

      await Task.Run(() => FirstTask3());

      // update the ui

   }
   catch (Exception exception)
   {
       // make sure you catch or do something with exception
   }
}

_{Note : Because this is an event and async void is appropriate, you need to make sure you deal with your exceptions (as this is unobserved). You might also want to guard against double clicks.}