c# - 为什么释放鼠标按钮时绘制的线会消失？

Question

我一直在研究 System.Drawing，除了一件事，我已经按照我希望的方式工作了。当我松开鼠标按钮时，这条线就消失了。

如何确保线条准确地保持在我离开的位置？

using System;
using System.Drawing;
using System.Windows.Forms;

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

            this.DoubleBuffered = true;
        }

        Graphics graphics;

        Random
            color = new Random(1);
        Int32
            penThickness = 1;
        Point
            currentCursorLocation, initialTouchLocation, touchOffset;
        Boolean
            mouseDown;

        protected override void OnPaint(PaintEventArgs e)
        {
            graphics = e.Graphics;

            if (mouseDown)
            {
                graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

                //DrawRectangle(graphics);
                //DrawEllipse(graphics);

                DrawLine(graphics);
            }
        }

        private void DrawRectangle(Graphics graphics)
        {
            graphics.DrawRectangle(new Pen(
                Color.FromArgb((color.Next(1, 
                255)), 
                (color.Next(1, 
                255)), 
                (color.Next(1, 
                255)))
                , 
                penThickness),
                currentCursorLocation.X,
                currentCursorLocation.Y,
                (this.Width / 2),
                (this.Height / 2)
                );
        }

        private void DrawEllipse(Graphics graphics)
        {
            graphics.DrawEllipse(new Pen(
                Color.FromArgb((color.Next(1, 255)),
                (color.Next(1, 255)),
                (color.Next(1, 255))), penThickness), 
                new RectangleF(currentCursorLocation, new Size(100, 100)));
        }

        private void DrawLine(Graphics graphics)
        {
            graphics.DrawLine(new Pen(
                Color.FromArgb((color.Next(1, 255)), 
                (color.Next(1, 255)), 
                (color.Next(1, 255))), penThickness),
                currentCursorLocation.X,
                currentCursorLocation.Y,
                touchOffset.X,
                touchOffset.Y
                );
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            currentCursorLocation = e.Location;
            this.Refresh();
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            if (!mouseDown)
            {
                touchOffset = e.Location;
                mouseDown = true;
            }
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            mouseDown = false;
        }
    }
}

Answer 1

您要求代码表现得像那样。所以它做同样的事情。

您在 Form1_MouseUp 事件中将 mouseDown 设置为 false。

private void Form1_MouseUp(object sender, MouseEventArgs e)
{
    mouseDown = false; //<--Here
}

然后你在绘制线条之前检查 if (mouseDown)。

protected override void OnPaint(PaintEventArgs e)
{
    graphics = e.Graphics;

    if (mouseDown)//<--Here
    {
        graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

        //DrawRectangle(graphics);
        //DrawEllipse(graphics);

        DrawLine(graphics);
    }
}

我猜你不需要 if (mouseDown) 检查 OnPaint 方法。

不确定您的意图是什么，如果您需要更多帮助，请在答案下方发表评论。