Question

我正在尝试开发一个“PictureBox”，它显示一个小圆圈“围绕”一个大圆圈。关键方面是这个小圆圈的位置（以及整个画面）可以根据我每秒钟进行的半昂贵的硬件调用而改变。我用一个“AngleValueTextBox”调用来代替。

研究关于该主题的几篇文章，这个似乎是这样做的正确方法：

public partial class Form1 : Form
{
  public Form1()
  {
    InitializeComponent();

    AngleValueTextBox_TextChanged(null, null); // Why doesn't this make the box appear on program start?
    PictureBox.Invalidate();  // Or this?
  }

  public class CircleCenterClass { public double X; public double Y; 
    public CircleCenterClass(double X, double Y) { this.X = X; this.Y = Y; }
  }

  CircleCenterClass GetCenterOfOrbitCircle(CircleCenterClass OrbitCenter, double OrbitRadius, double Angle)
  {
    CircleCenterClass Result = new CircleCenterClass(0, 0);
    Result.X = OrbitCenter.X + OrbitRadius * Math.Sin(Angle * (3.141592654 / 180));
    Result.Y = OrbitCenter.Y - OrbitRadius * Math.Cos(Angle * (3.141592654 / 180));
    return Result;
  }

  private void drawPictureBox(Graphics graphics, bool ownGraphics)
  {
    double Angle= 0; 
    // Normally this is an expensive hardware call which I don't want to make more than 
    // once a second.
    try {
      Double.TryParse(AngleValueTextBox.Text, out Angle);
    } catch (Exception e) {
      MessageBox.Show("Could not parse Angle " + 
                       AngleValueTextBox.Text);
    }

    using (Bitmap bitmap = new Bitmap(PictureBox.Width, PictureBox.Height))
    {
      using (Graphics gx = Graphics.FromImage(bitmap))
      {
        double OrbitedCircleRadius = 40;
        CircleCenterClass OrbitedCircleCenter = new CircleCenterClass(60, 60);
        double OrbitingCircleRadius = 7;
        Pen MyRedPen = new Pen(Color.Red, 2f);
        Brush MyBlackBrush = new SolidBrush(Color.Black);

        gx.DrawEllipse(MyRedPen, (Int32)(OrbitedCircleCenter.X - OrbitedCircleRadius),
                                        (Int32)(OrbitedCircleCenter.Y - OrbitedCircleRadius),
                                        (Int32)(2 * OrbitedCircleRadius),
                                        (Int32)(2 * OrbitedCircleRadius));

        CircleCenterClass CircleCenter = GetCenterOfOrbitCircle(
                            OrbitedCircleCenter, OrbitedCircleRadius,
                            Angle);

        gx.FillEllipse(MyBlackBrush, (Int32)(CircleCenter.X - OrbitingCircleRadius),
                                     (Int32)(CircleCenter.Y - OrbitingCircleRadius),
                                     (Int32)(2 * OrbitingCircleRadius),
                                     (Int32)(2 * OrbitingCircleRadius));

        // Draw Electronics box. 
        Graphics g = PictureBox.CreateGraphics();
        g.Clear(BackColor);
        g.DrawImage(bitmap, 0, 0);  
      }
    }
  }

  private void PictureBox_Paint(object sender, PaintEventArgs e)
  {
    drawPictureBox(e.Graphics,false);
  }

  private void AngleValueTextBox_TextChanged(object sender, EventArgs e)
  {
    drawPictureBox(PictureBox.CreateGraphics(), true);
  }
}

关键问题：

我无法让图片最初显示（即GUI启动时）。我已经尝试将事件添加到我的Form构造函数中（如您所见），但没有运气。什么是“正确”的方式？
有没有更好的方法来绘制不断变化的图形？

Answer 1

将draw方法调用添加到Form的Load事件。

Answer 2

使用CreateGraphics很少是更新显示的正确方法。只需让你的paint方法完成所有绘画并调用控件Invalidate（）方法来更新屏幕。
确保绘制事件已连线（只是为了确保）。如果没有在设计器中连接，请确保它在表单的构造函数中：

PictureBox.Paint += PictureBox_Paint;

另外，为控件命名。 PictureBox不是很具描述性。
任何“半昂贵的硬件调用”都应该在BackgroundWorker中进行，这样就不会冻结用户界面。
如果只是不断尝试使用新图纸更新屏幕，请使用计时器。
您不需要在每次绘制调用时都创建新的位图。使用给定的图形对象或使用仅在控件调整大小时创建的一个位图。

Answer 3

将PictureBox控件替换为名为PictureBox的Panel

或将图片框的Image属性设置为创建的位图

请注意，这不是一种特别有效的方法。

如果图像每秒只更新一次，那么你可能只在值改变时绘制到图像，将位图保持为窗体上的私有属性，只复制绘图中的位图（就像你做的那样，但是删除所有绘图代码，只在值更改时才执行此操作）

enter image description here

    Bitmap bitmap;
    public Form1()
    {
        InitializeComponent();
        bitmap = new Bitmap(PictureBox.Width, PictureBox.Height);
        AngleValueTextBox_TextChanged(null, null); // Why doesn't this make the box appear on program start?
        PictureBox.Invalidate();  // Or this?
    }

    public class CircleCenterClass
    {
        public double X; public double Y;
        public CircleCenterClass(double X, double Y) { this.X = X; this.Y = Y; }
    }

    CircleCenterClass GetCenterOfOrbitCircle(CircleCenterClass OrbitCenter, double OrbitRadius, double Angle)
    {
        CircleCenterClass Result = new CircleCenterClass(0, 0);
        Result.X = OrbitCenter.X + OrbitRadius * Math.Sin(Angle * (3.141592654 / 180));
        Result.Y = OrbitCenter.Y - OrbitRadius * Math.Cos(Angle * (3.141592654 / 180));
        return Result;
    }

    private void drawPictureBox(Graphics graphics, bool ownGraphics)
    {



    }

    private void DrawImage()
    {
        double Angle = 0;
        // Normally this is an expensive hardware call which I don't want to make more than 
        // once a second.
        try
        {
            Double.TryParse(AngleValueTextBox.Text, out Angle);
        }
        catch (Exception e)
        {
            MessageBox.Show("Could not parse Angle " +
                             AngleValueTextBox.Text);
        }

        using (Graphics gx = Graphics.FromImage(bitmap))
        {
            gx.Clear(BackColor);
            double OrbitedCircleRadius = 40;
            CircleCenterClass OrbitedCircleCenter = new CircleCenterClass(60, 60);
            double OrbitingCircleRadius = 7;
            Pen MyRedPen = new Pen(Color.Red, 2f);
            Brush MyBlackBrush = new SolidBrush(Color.Black);

            gx.DrawEllipse(MyRedPen, (Int32)(OrbitedCircleCenter.X - OrbitedCircleRadius),
                                            (Int32)(OrbitedCircleCenter.Y - OrbitedCircleRadius),
                                            (Int32)(2 * OrbitedCircleRadius),
                                            (Int32)(2 * OrbitedCircleRadius));

            CircleCenterClass CircleCenter = GetCenterOfOrbitCircle(
                                OrbitedCircleCenter, OrbitedCircleRadius,
                                Angle);

            gx.FillEllipse(MyBlackBrush, (Int32)(CircleCenter.X - OrbitingCircleRadius),
                                         (Int32)(CircleCenter.Y - OrbitingCircleRadius),
                                         (Int32)(2 * OrbitingCircleRadius),
                                         (Int32)(2 * OrbitingCircleRadius));
        }
    }

    private void PictureBox_Paint(object sender, PaintEventArgs e)
    {
        e.Graphics.DrawImage(bitmap, 0, 0);
    }

    private void AngleValueTextBox_TextChanged(object sender, EventArgs e)
    {
        DrawImage();
        PictureBox.Invalidate();
    }

让图形最初显示

3 个答案: