Form with ProgressBar is Frozen while reading file (C# WinForms)

Question

In my C# WinForms app, I have the MainForm in which I am using a BackgroundWorker to read a large Text file.

I am also using a second Form to display a Marquee ProgressBar to inform user that they must wait until file has been completely read.

The problem I am having is the Form with the progressbar (SimpleProgressBar) is frozen until the file is read. Where the BW should be on a separate thread to not let this happen.

I left the code that reads the file as it may be relevant to my problem. However all the code actually works its just that the Form to display the ProgressBar is frozen.

SimpleProgressBar.cs (Form)

//Simple Progress Bar set to Marquee
public partial class SimpleProgressBar : Form
{
    public SimpleProgressBar()
    {
        InitializeComponent();


        //ProgressBar is setup in the designer.
        /*
          System.Windows.Forms.ProgressBar progressBar1;
          this.progressBar1.Location = new System.Drawing.Point(16, 65);
          this.progressBar1.Name = "progressBar1";
          this.progressBar1.Size = new System.Drawing.Size(350, 23);
          this.progressBar1.Style = System.Windows.Forms.ProgressBarStyle.Marquee;
          this.progressBar1.TabIndex = 1;
        */

    }
}

MainForm.cs (Form)

    //Class variable
    private SimpleProgressBar wait = new SimpleProgressBar();



    private void generatePreview()
    {
            //Setup BW Thread
            BackgroundWorker worker = new BackgroundWorker();
            worker.WorkerReportsProgress = true;
            worker.WorkerSupportsCancellation = true;
            worker.DoWork += worker_DoWork;
            worker.ProgressChanged += worker_ProgressChanged;
            worker.RunWorkerCompleted += worker_RunWorkerCompleted;

            //Start procesing file
            worker.RunWorkerAsync();


            //Show the dialog
            wait.ShowDialog(); //perhaps .Show() would be better ?


    }

    //Once completed put the text into the textbox
    void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        textBox1.Text  = ((StringBuilder)e.Result).ToString();

    }

    //Report progress here
    void worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {


    }

    void worker_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker bw = (BackgroundWorker)sender;

        int bufferSize = 1024;

        var sb = new StringBuilder();
        var buffer = new Char[bufferSize];
        var length = 0L;
        var totalRead = 0L;
        var count = bufferSize; 

        using (var sr = new StreamReader("c:\200mb_text_file.txt"))
        {
            if (bw.CancellationPending)
            {

            }
            else
            {
                length = sr.BaseStream.Length;
                while (count > 0)
                {
                    count = sr.Read(buffer, 0, bufferSize);
                    sb.Append(buffer, 0, count);

                    totalRead += count;
                }
            }
        }

        e.Result = sb;


    }

UPDATE

So essentially I wanted to create a generic 2nd Form to use a a progress indicator that can be used for multiple purposes.

However it looks like that the BW MUST be on the same thread that hold the UI elements that need updating.

Answer 1

ShowDialog shows a modal dialog that you'll have to explicitly close. When you call ShowDialog, the program will not continue to execute beyond that point. Your background worker's completion event will have to close the dialog.

In addition, you're reading 1,024 bytes at a time and then calling the progress event. Every call to the progress event requires marshaling to the UI thread. It takes approximately zero time to read 1,024 bytes, which means that the progress event is being called continually, which in turn means that the UI thread is nearly 100% occupied with your progress update.

If you really need to report progress as the thing is loading, then use a larger buffer. You'll get better read performance anyway with a 64 Kilobyte buffer. That is:

int bufferSize = 65536;

But your files must be huge. You should be able to read at least 50 megabytes per second unless you have a really slow disk or you're reading over a slow network.

Answer 2

Progress Bar needs to be updated in another Thread.Updating the progress bar from the UI thread will cause freezing issues. Just put the code to update the progres bar in the Backgroudnworker's DOWork Method rather than reporting it.

 void worker_DoWork(object sender, DoWorkEventArgs e)
    {
    stuffdone()
    progressBar1.PerformStep();

    }

Before using this you will need to set Form.CheckForIllegalCrossThreadCalls = false; so that BW can access the UI