Question

C#画圆问题

画三个圆，分别上色。这个我都做了，但是现在需要用一个textbox让用去输入圆的半径，从而改变圆的大小，请问各位大神，这个怎么弄？另外还有就是给这三个圆描上黑的边。

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

private void button3_Click(object sender, EventArgs e)
{
Graphics paper = pictureBoxDisplay.CreateGraphics();
SolidBrush aBrush = new SolidBrush(Color.Green);
Rectangle bar = new Rectangle(10, 10, 50, 50);
paper.FillEllipse(aBrush, bar);

bar.Y += 80;
aBrush.Color = Color.Yellow;
paper.FillEllipse(aBrush, bar);

bar.Y += 80;
aBrush.Color = Color.Red;
paper.FillEllipse(aBrush, bar);
少打了一个字，让用户

Answer 1

        private void button1_Click(object sender, EventArgs e)
        {
            int diameter;
            try
            {
                diameter = int.Parse(textBox1.Text);
            }
            catch
            {
                MessageBox.Show("直径值错误!");
                return;
            }
            Rectangle rect = new Rectangle(10, 10, diameter, diameter);
            
            Graphics g = pictureBox1.CreateGraphics();
            
            //清除原来画的圆
            g.Clear(pictureBox1.BackColor);

            //画圆——绿色
            Brush brush = new SolidBrush(Color.Green);
            g.FillEllipse(brush, rect);
            //描边
            Pen pen = Pens.Black;
            g.DrawEllipse(pen, rect);

            //画圆——黄色
            rect.Y += 80;
            brush = new SolidBrush(Color.Yellow);
            g.FillEllipse(brush, rect);
            //描边
            g.DrawEllipse(pen, rect);

            //画圆——红色
            rect.Y += 80;
            brush = new SolidBrush(Color.Red);
            g.FillEllipse(brush, rect);
            //描边
            g.DrawEllipse(pen, rect);

            g.Dispose();
        }

Answer 2

FillEllipse函数，用来填充一个矩形的内部椭圆的。当矩形尺寸变小的时候，椭圆也就变小了。
你这里的矩形bar创建的时候，使用Rectangle(10, 10, 50, 50);，自己修改一下尺寸就可以了。
描黑边，实际上就是用黑色画笔画一个圆。使用Graphics类的DrawEllipse函数（填充用FillEllipse）

Answer 3

            Point center = new Point(20, 20);
            Graphics paper = pictureBoxDisplay.CreateGraphics();
            paper.Clear(this.BackColor);
            SolidBrush aBrush = new SolidBrush(Color.Green);
            Pen blackPen = new Pen(Color.Black, 1);
            int r = int.Parse(textBox1.Text);

            Rectangle bar = new Rectangle(center.X-r,center.Y-r,center.X+r,center.Y+r);
            paper.FillEllipse(aBrush, bar);
            paper.DrawEllipse(blackPen, bar);

           bar.Y += 80;
           aBrush.Color = Color.Yellow;
           paper.FillEllipse(aBrush, bar);
           paper.DrawEllipse(blackPen, bar);
           bar.Y += 80;
           aBrush.Color = Color.Red;
           paper.FillEllipse(aBrush, bar);
           paper.DrawEllipse(blackPen, bar);