Question

C#通过不同按钮在picturebox上画出圆、三角形

RT
很简单的一个问题呐，主要是牵扯到那些refresh()还有一个保存之前的图像的问题
给点代码研究一下吧，按钮的click事件怎么跟picturebox的paint事件联系起来呢？我要代码啊~~

Answer 1

可以在定义一个form 的成员来表示要画什么形状，比如一个整数叫 iSharp, 约定0是没有，1是圆2是方什么的。

在按扭click时，按不同的按钮的功能来更新这个iSharp的值，更新为1，2，删除按钮被按就更新为0. 然后，调用picturebox的Invalidate方法，这个方法会引起picturebox重绘。

最后，重写PictureBox的OnPaint方法，或是响应Paint事件，根据iShaper的值来绘出不同的图形。

以下是有保存功能的代码。就是不直接画在picturebox上，而是画在一个Bitmap上，然后把bitmap画到界面上。保存时，只要保存这个bitmap就行了。

public partial class Form2 : Form
{
        // ... ...
       
        private int iSharp = 0;
        private Bitmap bmp = null;

        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            bmp = new Bitmap(this.pictureBox1.Width, this.pictureBox1.Height, e.Graphics);
            var g = Graphics.FromImage(bmp);

            g.Clear(Color.White);

            switch (this.iSharp)
            {
                case 0:
                    break;
                case 1:
                    g.DrawEllipse(Pens.Black, 
                        new Rectangle(1,1, 
                            this.pictureBox1.Width -2, 
                            this.pictureBox1.Height - 2 ));

                    break;
                case 2:
                    g.DrawRectangle(Pens.Blue, 
                        new Rectangle(1,1, 
                            this.pictureBox1.Width -2, 
                            this.pictureBox1.Height - 2 ));
                    break;
                case 3:
                    g.DrawPolygon(Pens.DarkGreen,
                        new Point[]{
                            new Point(1, this.pictureBox1.Height -1),
                            new Point( this.pictureBox1.Width - 1 , this.pictureBox1.Height -1),
                            new Point(this.pictureBox1.Width/2, 1),

                        });
                    break;
                default:
                    g.DrawString("不支持", 
                        new Font("宋体", 10.0f), 
                        Brushes.Red, 0,0, 
                        StringFormat.GenericDefault);
                    break;
            }
            e.Graphics.DrawImage(bmp, 0, 0);
        }

        private void btnCircle_Click(object sender, EventArgs e)
        {
            this.iSharp = 1;
            this.pictureBox1.Invalidate();
        }

        private void btnDelete_Click(object sender, EventArgs e)
        {
            this.iSharp = 0;
            this.pictureBox1.Invalidate();
        }

        private void btnRect_Click(object sender, EventArgs e)
        {
            this.iSharp = 2;
            this.pictureBox1.Invalidate();
        }

        private void btnTran_Click(object sender, EventArgs e)
        {
            this.iSharp = 3;
            this.pictureBox1.Invalidate();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            bmp.Save("c:\\1.jpg", ImageFormat.Jpeg);
        }
}

Answer 2

        private int i = 0;
        private void button1_Click(object sender, EventArgs e)
        {
            i = 1;
            pictureBox1.Refresh();
        }
        private void button2_Click(object sender, EventArgs e)
        {
            i = 2;
            pictureBox1.Refresh();
        }
        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            Graphics gh = e.Graphics;
            Pen p = new Pen(Color.Red);
            if (i == 1)
            {
                gh.DrawEllipse(p, 0, 0, 100, 100);
            }
            else if (i == 2)
            {
                gh.DrawLine(p, 0, 0, 100, 100);
            }
        }