The BackgroundWorker RunWorkerAsync method does not trigger DoWork();

Question

I've been trying to get the BackGroundWorker to work for hours now. I can't seem to find out why my DoWork() eventhandler isn't getting raised after calling bgw.RunWorkerAsync();

I've cut down the irrelivant code, so it's a bit easyer to read.

namespace FolderMonitor
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.IO;
    using System.Linq;
    using System.Text;
    using System.Threading;
    using System.Threading.Tasks;
    using System.Windows.Forms;

    using FolderMonitor.Properties;

    public partial class MainForm : Form
    {
        private ExistingFileHandler exist = new ExistingFileHandler();
        private MonitoredFileHandler handler = new MonitoredFileHandler();
        private Monitor monitor;
        private BackgroundWorker bgw = new BackgroundWorker();

        public MainForm(Monitor monitor)
        {
            this.monitor = monitor;
            InitializeComponent();
            InitializeBackgroundWorker();
            txtFolderPath.Text = Settings.Default.monitoredFolder;
            txtNewFolderPath.Text = Settings.Default.destinationFolder;
            btnStop.Enabled = false;
        }

        private void InitializeBackgroundWorker()
        {
            bgw.DoWork += new DoWorkEventHandler(bgw_DoWork);
            bgw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bgw_RunWorkerCompleted);
            bgw.ProgressChanged += new ProgressChangedEventHandler(bgw_ProgressChanged);
        }

        private void BtnStart_Click(object sender, EventArgs e)
        {
            btnStop.Enabled = true;
            btnStart.Enabled = false;
            exist.HandleExistingFiles(txtFolderPath.Text);
            listBoxFiles.Items.Clear();
            MonitoredFileHandler.MonitoredFolderPath = txtFolderPath.Text;
            MonitoredFileHandler.DestinationFolderPath = txtNewFolderPath.Text;
            this.bgw.RunWorkerAsync();
        }

        private void BtnStop_Click(object sender, EventArgs e)
        {
            this.bgw.CancelAsync();
            btnStart.Enabled = true;
            btnStop.Enabled = false;
        }

        private void bgw_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker worker = sender as BackgroundWorker;

            if (!worker.IsBusy)
            {
                monitor.StartFolderMonitor(txtFolderPath.Text);
            }
        }

        private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            btnStart.Enabled = true;
            btnStop.Enabled = false;
        }

        private void bgw_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            handler.MonitoredFiles.Add(txtNewFolderPath.Text);
        }
    }
}

Answer 1

BackgroundWorker.IsBusy will be true after its background thread been started, so it will always be true where you are testing it inside bgw_DoWork() . Therefore, monitor.StartFolderMonitor(txtFolderPath.Text) will never be called.

What are you trying to test for? I think you can just remove the if (!worker.IsBusy) check.

Answer 2

除了前面提到的IsBusy问题之外，StartFolderMonitor以start开头而不是DoFolderMonitoring或类似的事实，这可能是非阻塞的，因此DoWork处理程序立即退出。

Answer 3

Just call

System.Windows.Forms.Application.DoEvents();

before bgw.RunWorkAsync();