Why does the Form_Paint event run continuously and only draw

Dong Lam Trien

I have the following code, I put a label in Form_Paint to track the number jump, I see the label jumping continuously but e.Graphics.DrawString(...) only looks once, does anyone know why ?

public partial class Form1: Form {
public Form1() {
InitializeComponent();
//progressBar1.Visible = false;
progressBar1.Minimum = 0;
progressBar1.Maximum = 100;
this.Paint += new System.Windows.Forms.PaintEventHandler(this.Form1_Paint);
}
int iNum = 0;
private void btnDrawText_Click(object sender, EventArgs e) //PaintEventArgs e
{
progressBar1.Value = 0;
progressBar1.Visible = true;
this.timer1.Interval = 100;
this.timer1.Enabled = true;
}
private void ShadowedTextPaint(PaintEventArgs e, int num) {
using(Font font1 = new Font("Times New Roman", 250, FontStyle.Bold, GraphicsUnit.Pixel)) {
PointF pointF1 = new PointF(310, 270);
e.Graphics.DrawString(num.ToString(), font1, Brushes.LightGreen, pointF1);
lblNum.Text = num.ToString();
}
}
private void Form1_Paint(object sender, PaintEventArgs e) {
ShadowedTextPaint(e, iNum);
}
private void timer1_Tick(object sender, EventArgs e) {
if (progressBar1.Value < 100) {
Random rd = new Random();
iNum = rd.Next(0, 999);
progressBar1.Value++;
} else {
this.timer1.Enabled = false;
progressBar1.Visible = false;
}
}
}

6 Replies

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Jefferson S. Motta6y ago
It's not Paint event that you need to do that.

https://docs.microsoft.com/en-us/dotnet/framework/winforms/advanced/how-to-draw-text-on-a-windows-form
public void DrawString()
{
    System.Drawing.Graphics formGraphics = this.CreateGraphics();
    string drawString = "Sample Text";
    System.Drawing.Font drawFont = new System.Drawing.Font("Arial", 16);
    System.Drawing.SolidBrush drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.Black);
    float x = 150.0F;
    float y = 50.0F;
    System.Drawing.StringFormat drawFormat = new System.Drawing.StringFormat();
    formGraphics.DrawString(drawString, drawFont, drawBrush, x, y, drawFormat);
    drawFont.Dispose();
    drawBrush.Dispose();
    formGraphics.Dispose();
}
Dong Lam Trien6y ago
I have written how to use label control, I am learning how to write a Form_Paint event why it cannot output random numbers.
Jefferson S. Motta6y ago
Abandon this,

put in the timer an update to a Label with font new Font("Times New Roman", 250, FontStyle.Bold, GraphicsUnit.Pixel)) It's painless.
Rajanikant Hawaldar6y ago
For what purpose your using paint event? To update label text and progress bar?
Dong Lam Trien6y ago
I understand you say, do you think there is a way to use Form_Paint to draw random numbers continuously over time ?
Rajanikant Hawaldar6y ago
Hi Dong Lam Triem, The paint event is raised when the window is rendered. This event occurs after the load event for a window, and reoccurs each time the window needs to be re-rendered, such as when another window obscures it and is then cleared away.