为什么我不能在图片框中用这段代码画一个矩形？

Question

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 UTUResultWithCoordinates
{
    public partial class GetCoordinates : Form
    {
        private string sem;
        private string branch;
        private int mouseisdown = 0;
        private int recx = 0;
        private int recy = 0;
        private int mousemovingwhilepressed = 0;
        public GetCoordinates()
        {
            InitializeComponent();
        }
        public GetCoordinates(string p, string p_2)
        {
            // TODO: Complete member initialization
            InitializeComponent();
            branch = p;
            sem = p_2;
            pictureBox1.Controls.Add(pictureBox2);
            pictureBox2.Location = new Point(0, 0);
            pictureBox2.BackColor = Color.Transparent;
            pictureBox2.Width = 1191;
            pictureBox2.Height = 842;
        }
        private void GetCoordinates_Load(object sender, EventArgs e)
        {
            pictureBox1.ImageLocation =        @"D:DotNetUTUResultWithCoordinatesUTUResultWithCoordinatesbinDebugComputerScience6.jpg";
        }



        private void pictureBox2_Paint(object sender, PaintEventArgs e)
        {
            if (mouseisdown == 1 && mousemovingwhilepressed==1)
            {
            System.Drawing.Graphics graphicsObj;
            graphicsObj = this.CreateGraphics();
            Pen myPen = new Pen(System.Drawing.Color.Blue, 100);
            Rectangle myRectangle = new Rectangle(recx, recy, 20, 20);
            e.Graphics.DrawRectangle(myPen, myRectangle);
         }
    }
    private void pictureBox2_MouseDown(object sender, MouseEventArgs e)
    {
        mouseisdown = 1;
        recx = e.X;
        recy = e.Y;
        pictureBox2.CreateGraphics();
    }
    private void pictureBox2_MouseMove(object sender, MouseEventArgs e)
    {
        label1.Text = e.X + "," + e.Y;
        mousemovingwhilepressed = 1;
        recx = e.X;
        recy = e.Y;
        pictureBox2.CreateGraphics();
    }
    private void pictureBox2_MouseUp(object sender, MouseEventArgs e)
    {
        mousemovingwhilepressed = 0;
        mouseisdown = 0;
        pictureBox2.CreateGraphics();
    }
}

}

我创建了一个显示图像的pictureBox1。然后，我在里面创建了一个 pictureBox2，这样我就可以通过拖动鼠标在该图像上绘制一个矩形。但是单击鼠标时没有任何反应。错误是什么？

Answer 1

调用 CreateGraphics 不会触发 PictureBox 的绘制。

使用"无效"导致重绘。

有关完整示例，请参阅：如何在 C# 中使用鼠标在 PictureBox.Image 上选择一个区域

旁注：

• 在构造函数以外的方法中调用 InitializeControl 不是一个好主意。
• 当您需要布尔值时，请使用布尔值，而不是整数。
• 实现 IDisposable 的对象（如笔）应尽可能少地创建，并在不再需要/使用时释放。