在PictureBox中显示图像，然后我鼠标圈选某一局部图像，怎么显示圈选的矩形框？

Question

我在MouseMove事件中Graphics graphics = this.CreateGraphics();
                Pen myPen = new Pen(Color.Red, 2);
                graphics.DrawRectangle(myPen, ptStart.X, ptStart.Y, e.X - ptStart.X, e.Y - ptStart.Y);
使用画矩形框，一点反应也没有，请问怎么实现我的目的呢？private void pb_InqImagePart_MouseDown(object sender, MouseEventArgs e)
        {
            pictureOperation = PICTURE_OPERATION.START;
            ptStart          = new Point(e.X, e.Y);
        }        private void pb_InqImagePart_MouseMove(object sender, MouseEventArgs e)
        {
            if (pictureOperation == PICTURE_OPERATION.START)
            {
                pictureOperation = PICTURE_OPERATION.WORKING;
                Graphics graphics = this.CreateGraphics();
                Pen myPen = new Pen(Color.Red, 2);
                graphics.DrawRectangle(myPen, ptStart.X, ptStart.Y, e.X - ptStart.X, e.Y - ptStart.Y);
            }           
        }        private void pb_InqImagePart_MouseUp(object sender, MouseEventArgs e)
        {
            if (pictureOperation == PICTURE_OPERATION.WORKING)
            {
                ptEnd = new Point(e.X, e.Y);
                RectangleF rect = new RectangleF(ptStart.X / pb_InqImagePart.Width, ptStart.Y / pb_InqImagePart.Height,
                                                (ptEnd.X - ptStart.X) / pb_InqImagePart.Width,
                                                (ptEnd.Y - ptStart.Y) / pb_InqImagePart.Height);
                if (selectInquireNode!=null)
                {
                    selectInquireNode.CloneImage(rect, System.Drawing.Imaging.PixelFormat.DontCare);
                }
                pictureOperation = PICTURE_OPERATION.IDLE;
            }
        }

Answer 1

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;namespace ERP
{
    public partial class Form13 : Form
    {
        public Form13()
        {
            InitializeComponent();
        }        private void button1_Click(object sender, EventArgs e)
        {
          
        }
        Point start = new Point();
        bool state = false;
        private void Form13_MouseDown(object sender, MouseEventArgs e)
        {
            start.X = e.X;
            start.Y = e.Y;
            state = true;
        }        private void Form13_MouseMove(object sender, MouseEventArgs e)
        {
            if (state)
            {
              
                Graphics gs = this.CreateGraphics();
                gs.Clear(Color.Red);
                Rectangle Rect = new Rectangle();
                Rect.X = start.X;
                Rect.Y = start.Y;
                Rect.Height = e.Y - start.Y;
                Rect.Width = e.X - start.X;
                gs.DrawRectangle(Pens.Purple, Rect);
               
            }
        }        private void Form13_MouseUp(object sender, MouseEventArgs e)
        {
            state = false;
        }
    }
}

Answer 2

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace WindowsApplication236
{
    public partial class Form1 : Form
    {
        Point StartPoint;        public Form1()
        {
            InitializeComponent();            this.MouseMove += new MouseEventHandler(Form1_MouseMove);         }        void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button != MouseButtons.Left)
                StartPoint = e.Location;
            else using (Graphics G = this.CreateGraphics())
                {
                    G.Clear(this.BackColor);  
                    G.DrawRectangle(Pens.Red, new Rectangle(StartPoint, new Size(e.X - StartPoint.X, e.Y - StartPoint.Y)));
                }
        }
    }
}

Answer 3

支持任何方向的拉伸using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace WindowsApplication236
{
    public partial class Form1 : Form
    {
        Point StartPoint;        public Form1()
        {
            InitializeComponent();            this.MouseMove += new MouseEventHandler(Form1_MouseMove);        }        void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button != MouseButtons.Left)
                StartPoint = e.Location;
            else using (Graphics G = this.CreateGraphics())
                {
                    Point Start = StartPoint;
                    Point End = e.Location;
                    int Width = e.X - Start.X;
                    int Height = e.Y - Start.Y;                    if (Width < 0)
                    {
                        Start.X += Width;
                        End.X -= Width;
                    }
                    if (Height < 0)
                    {
                        Start.Y += Height;
                        End.Y -= Height;
                    }                    G.Clear(this.BackColor);                    G.DrawRectangle(Pens.Red, new Rectangle(Start, new Size(Math.Abs(Width), Math.Abs(Height))));
                }
        }
    }
}