text on progressbar in c# [closed]

问题:

I am using the following code.

Why does it not run properly ?

private void Form1_Shown(object sender, EventArgs e)
{
    for (int i = 1; i <= 100; i++)
    {
        Application.DoEvents();
        Thread.Sleep(200);

        progressBar1.Refresh();
        progressBar1.Value = i;
        progressBar1.CreateGraphics().DrawString(i.ToString() + "%",
            new Font("Arial", (float)8.25, FontStyle.Regular),
            Brushes.Black, new PointF(progressBar1.Width / 2 - 10,
                progressBar1.Height / 2 - 7));


    }
}

update :

Why does not always show the text ?

回答1:

This works - although I'd set the thread-sleep to more than 200 ms. Your problem was that you did the work in the UI thread and this way it never gets updated. For better visibility, just change the font color:

 private void Form1_Load(object sender, EventArgs e)
{
  Task t = new Task(() => StartUpdate());
  t.Start();

  t.ContinueWith(task => Console.WriteLine("Done loading"));
}

 private void StartUpdate()
{
  for (int i = 1; i <= 100; i++)
  {
    UpdateProgressBar(i);
  }
}

private void UpdateProgressBar(int i)
{
  if (progressBar1.InvokeRequired)
  {
    progressBar1.Invoke(new Action<int>(UpdateProgressBar), new Object[] { i });
  }
  else
  {
    Thread.Sleep(200);
    progressBar1.Refresh();
    progressBar1.Value = i;
    progressBar1.CreateGraphics().DrawString(i.ToString() + "%", new Font("Arial",
                                          (float)10.25, FontStyle.Bold),
                                          Brushes.Red, new PointF(progressBar1.Width / 2 - 10, progressBar1.Height / 2 - 7));
  }
} 

回答2:

Use this. There are good ways of doing this but as your question was why it wasn't working, its because of the Application.DoEvents();

    private void Main_Shown(object sender, EventArgs e)
    {
        for (int i = 1; i <= 100; i++)
        {
            progressBar1.Value = i;
            int percent = (int)(((double)(progressBar1.Value -progressBar1.Minimum) / (double)(progressBar1.Maximum - progressBar1.Minimum)) * 100);
            using (Graphics gr = progressBar1.CreateGraphics())
            {
                gr.DrawString(percent.ToString() + "%",  SystemFonts.DefaultFont, Brushes.Black, new PointF(progressBar1.Width / 2 - (gr.MeasureString(percent.ToString() + "%", SystemFonts.DefaultFont).Width / 2.0F), progressBar1.Height / 2 - (gr.MeasureString(percent.ToString() + "%", SystemFonts.DefaultFont).Height / 2.0F)));
            }
            System.Threading.Thread.Sleep(200);
        }
    }