不能在窗體加載繪製橢圓c＃

Question

我想繪製一個在c＃中的formload上包含PNG的圖片框中的一些橢圓。當我在下面執行代碼時，我會看到我的橢圓半秒鐘，然後我再也看不到它們了。

當我點擊我的圖片框時，我可以繪製一個橢圓，但是當我最小化表單時，它們不會再出現。

我讀過你不應該把你的繪圖代碼放在formload中，而是在OnPaint方法中，這是我所做的。我不知道該怎麼試。謝謝。 （請注意，我已經留下了一些代碼評論，以顯示我已經嘗試過）。

public partial class FormParterre : Form 
{ 
    Graphics g; 
    float circleSize = 15; 
    //Brushes rouge = new Brushes (Brushes.Red); 

    ReservationBilletSiegeDAO reservationBilletSiegeDAO = new ReservationBilletSiegeDAO(); 
    SiegeDAO siegeDAO = new SiegeDAO(); 

    List <Siege> sieges; 
    List<ReservationBilletSiege> rbs; 
    ReservationBillet reservationBillet = new ReservationBillet(); 
    ReservationBilletSiege reservationBilletSiege; 

    SolidBrush semiTransBrush; 


    public FormParterre() 
    { 
     InitializeComponent(); 
     pictureBox1.Image = new Bitmap("./parterre.png"); 
     g = pictureBox1.CreateGraphics(); 


    } 

    public FormParterre(ReservationBillet rb) 
    { 
     reservationBillet = rb; 
     pictureBox1.Image = new Bitmap("./parterre.png"); 
     g = pictureBox1.CreateGraphics(); 



     InitializeComponent(); 
    } 

    protected override void OnPaintBackground(PaintEventArgs e) 
    { 
     // do nothing! prevents flicker 
    } 

    protected override void OnPaint(PaintEventArgs e) 
    { 

     sieges = siegeDAO.readAll(); 

     rbs = reservationBilletSiegeDAO.readAll(); 

     foreach (ReservationBilletSiege reservationBilletSiegeTMP in rbs) 
     { 
      Console.WriteLine(reservationBilletSiegeTMP.toString()); 
      int x = siegeDAO.read(reservationBilletSiegeTMP.idSiege).xValeur; 
      int y = siegeDAO.read(reservationBilletSiegeTMP.idSiege).yValeur; 
      float xx = (float)x; 
      float yy = (float)y; 
      Console.WriteLine("le x: " + xx); 
      Console.WriteLine("le y: " + yy); 


       /*e.Graphics.FillRectangle(new SolidBrush(BackColor), e.ClipRectangle);*/ 
      g.FillEllipse(new SolidBrush(Color.FromArgb(128, 0, 0, 255)), xx - circleSize/2, yy - circleSize/2, circleSize,          circleSize); 
     } 

    } 

    private void pictureBox1_Click(object sender, EventArgs e) 
    { 
     MouseEventArgs me = (MouseEventArgs)e; 
     txtX.Text = me.X.ToString(); 
     txtY.Text = me.Y.ToString(); 

     Console.WriteLine("click"); 

     g.FillEllipse(new SolidBrush(Color.FromArgb(128, 0, 0, 255)), float.Parse(txtX.Text) - circleSize/2, float.Parse(txtY.Text) - circleSize/2, circleSize, circleSize); 





    } 

    private void FormParterre_Shown(object sender, EventArgs e) 
    { 

    } 

    private void FormParterre_Load(object sender, EventArgs e) 
    { 

     /*sieges = siegeDAO.readAll(); 
     //semiTransBrush = new SolidBrush(Color.FromArgb(128, 0, 0, 255)); 



     rbs = reservationBilletSiegeDAO.readAll(); 

     foreach (ReservationBilletSiege reservationBilletSiegeTMP in rbs) 
     { 
      Console.WriteLine(reservationBilletSiegeTMP.toString()); 
      int x = siegeDAO.read(reservationBilletSiegeTMP.idSiege).xValeur; 
      int y = siegeDAO.read(reservationBilletSiegeTMP.idSiege).yValeur; 
      float xx = (float)x; 
      float yy = (float)y; 
      Console.WriteLine("le x: " + xx); 
      Console.WriteLine("le y: " + yy); 

      g.FillEllipse(new SolidBrush(Color.FromArgb(128, 0, 0, 255)), xx - circleSize/2, yy - circleSize/2, circleSize, circleSize); 
     }*/ 
    } 


} 

Answer 1

您需要使用它傳遞給你的PaintEventArgs.Graphics屬性OnPaint方法作畫。如果您想在PictureBox上畫畫，您可以嘗試訂閱其Paint活動並在那裏繪畫。

這個工作對我來說：

public void Form1() 
{ 
    InitializeComponent(); 

    pictureBox1.Paint += pictureBox1_Paint; 
} 

private void pictureBox1_Paint(object sender, PaintEventArgs e) 
{ 
    e.Graphics.FillEllipse(Brushes.Red, pictureBox1.ClientRectangle); 
}