C# Winform ProgressBar and BackgroundWorker

问题:

I have the following problem:

I have a Form named MainForm. I have a long operation to be taken place on this form.

While this long operation is going on, I need to show another from named ProgressForm on top of the MainForm.

ProgressForm contains a progress bar which needs to be updated while the long operation is taking place.

After the long operation is completed, the ProgressForm should be closed automatically.

I have written the following code:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Threading;

namespace ClassLibrary
{
    public class MyClass
    {
        public static string LongOperation()
        {
            Thread.Sleep(new TimeSpan(0,0,30));

            return "HelloWorld";
        }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace BackgroungWorker__HelloWorld
{
    public partial class ProgressForm : Form
    {
        public ProgressForm()
        {
            InitializeComponent();
        }

        public ProgressBar ProgressBar
        {
            get { return this.progressBar1; }
            set { this.progressBar1 = value; }
        }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

using ClassLibrary;

namespace BackgroungWorker__HelloWorld
{
    public partial class MainForm : Form
    {
        ProgressForm f = new ProgressForm();

        public MainForm()
        {
            InitializeComponent();  
        }

        int count = 0;
        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            if (f != null)
            {
                f.ProgressBar.Value = e.ProgressPercentage;
            }

            ++count;
        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Cancelled) 
            {  
                MessageBox.Show("The task has been cancelled");  
            }  
            else if (e.Error != null)  
            {                  
                MessageBox.Show("Error. Details: " + (e.Error as Exception).ToString());  
            }  
            else 
            {  
                MessageBox.Show("The task has been completed. Results: " + e.Result.ToString());  
            }
        }


        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            if (f == null)
            {
                f = new ProgressForm();
            }

            f.ShowDialog();

            //backgroundWorker1.ReportProgress(100);

            MyClass.LongOperation();

            f.Close();
        }

        private void btnStart_Click(object sender, EventArgs e)
        {
            backgroundWorker1.RunWorkerAsync();
        }

        private void btnCancel_Click(object sender, EventArgs e)
        {
            backgroundWorker1.CancelAsync();

            this.Close();
        }
    }
}

I can't find a way to update the progressBar.

Where should I place backgroundWorker1.ReportProgress() and how should I call this?

I must not make any change in MyClass because I don't know what would happen or how long it takes to complete the operation in this layer of my application.

Can anyone help me?

回答1:

One problem is that you're sleeping for 30 seconds. Normally you'd call ReportProgress at various points within your long-running task. So to demonstrate this, you might want to change your code to sleep for 1 second, but 30 times - calling ReportProgress each time it finishes a sleep.

Another problem is that you're showing your ProgressForm from the background thread. You should start it in the UI thread, but hook the background worker's ProgressChanged event to it. Then when the background worker reports progress, the progress form will be updated.

回答2:

ReportProgress is the method which you'll have to call in your 'working' method. This method will raise the 'ProgressChanged' event.

In your form, you can attach an eventhandler to the ProgressChanged event. Inside that eventhandler, you can change the position of the progressbar. You can also attach an eventhandler to the RunWorkerCompleted event, and inside that eventhandler, you can close the form which contains the progressbar.

回答3:

It should be noted you need to set

backgroundWorker1.WorkerReportsProgress = true;

if you want the background worker to raise the ProgressChanged event and

backgroundWorker1.WorkerSupportsCancellation = true;

if you wish to be able to cancel the worker thread.

As the others have said, run the f.ShowDialog() in your UI thread and use ProgressChanged to update the ProgressWindow.

To get the ProgressForm to self close, in backgroundWorker1_RunWorkerCompleted, call f.Close(); This means the long operation has completed and we can close the window.

回答4:

What is needed here is to not pass the entire main form to the class, but simply the instance of your BackgroundWorker! You need to cast the sender as Background worker like so:

private void bgWorker_DoWork(object sender DoWorkEventArgs e)
{
    // Get the BackgroundWorker that raised this event
    BackgroundWorker worker = sender as BackgroundWorker;

    // And now you just send worker to whatever class you need like so:
    bgArgs args = e.Argument as bgArgs;
    MyClass objMyClass = new MyClass();

    MyClass.MyMethod(strValue, args.Option, worker);

    // Do something based on return value.
}

And then in your MyClass.MyMethod() you would do the progress calculations and simply raise the worker.ReportProgress(int percentage) event to update the progress bar or whatnot on your main UI form!

This should work perfectly!

Check out this MSDN article for more details, see their Fibonacci example, it's what they do since CalculateFibonacci is a custom class which sends updates to Main form's UI.

See MSDN BackgroundWorker Class for more details.