在面板上用鼠标画一条线 [英] Drawing a line by mouse in a panel

问题描述

我想用鼠标（交互式地）绘制一条线，我使用了C＃和WinForm，该线应该在从起点（当在面板上按下鼠标时）到鼠标的当前位置的任何时间出现就像在 Paint 程序中画一条线。

I want to draw a line by mouse(interactively) , I used C# and WinForm, the line should appear at any time from the starting point(when the mouse press on the panel) to the current position of the mouse, exactly like drawing a line in Paint program.

但是代码产生很多行，我知道为什么，但我不知道如何克服这个问题

but the code produces a lot of lines, i know why but i don't know how to overcome this problem

这是我的代码：

namespace WindowsFormsApplication2
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    Graphics g;
    Pen myPen = new Pen(Color.Red);
    Point p = new Point();
    bool flag = false;


    private void panel1_MouseDown(object sender, MouseEventArgs e)
    {
        flag = true;
        p = e.Location;
    }

    private void panel1_MouseMove(object sender, MouseEventArgs e)
    {
        if (flag)
        {
            g = panel1.CreateGraphics();
            myPen.Width = 3;

            Point p2 = new Point();
            p2 = e.Location;

            g.DrawLine(myPen, p, p2);

        }
    }

    private void panel1_MouseUp(object sender, MouseEventArgs e)
    {
        flag = false;
    }

}}

有帮助吗？我想画很多线并使代码尽可能简单！

Any Help? i want to draw many lines and keep the code simple as possible!

推荐答案

您将需要更好地管理绘图。一些指针：

You will need to better manage the drawing. Some pointers:

1. 不要使用 CreateGraphics 。而是使用控件已提供的 Paint 事件。


2. 在您自己的继承类中绘制图形。除非您在表单上绘制 ，否则不要绘制 Form 类。

1. Don't use CreateGraphics. Instead, use the Paint event already provided by the control.
2. Do your drawing in an inherited class of your own. Don't draw in the Form class unless you're drawing on the form.

这是一个示例类。它是从 Panel 继承的。只需将其添加到窗体中，例如使用 this.Controls.Add（new PanelWithMouseDraw（））; 。

Here's an example class. It's inherited from Panel. Simply add this to a form, such as in the Form's constructor using something like this.Controls.Add(new PanelWithMouseDraw());.

注意：这使用了元组，我认为它需要.NET 4.0或更高版本。您可以用其他内容替换此结构，如果需要...，您只需要保存 Point 对的列表。

Note: this uses Tuple which I believe requires .NET 4.0 or above. You could replace this structure with something else, if need be...you just need to keep a list of Point pairs.

namespace WindowsFormsApplication1
{
    public class PanelWithMouseDraw : Panel
    {
        private Point _origin = Point.Empty;
        private Point _terminus = Point.Empty;
        private Boolean _draw = false;
        private List<Tuple<Point, Point>> _lines = new List<Tuple<Point, Point>>();

        public PanelWithMouseDraw()
        {
            Dock = DockStyle.Fill;
            DoubleBuffered = true;
        }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);
            if (e.Button == MouseButtons.Left)
            {
                _draw = true;
                _origin = e.Location;
            }
            else
            {
                _draw = false;
                _origin = Point.Empty;
            }

            _terminus = Point.Empty;
            Invalidate();
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            base.OnMouseUp(e);
            if (_draw && !_origin.IsEmpty && !_terminus.IsEmpty)
                _lines.Add(new Tuple<Point, Point>(_origin, _terminus));
            _draw = false;
            _origin = Point.Empty;
            _terminus = Point.Empty;
            Invalidate();
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);
            if (e.Button == MouseButtons.Left)
                _terminus = e.Location;
            Invalidate();
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            foreach (var line in _lines)
                e.Graphics.DrawLine(Pens.Blue, line.Item1, line.Item2);
            if (!_origin.IsEmpty && !_terminus.IsEmpty)
                e.Graphics.DrawLine(Pens.Red, _origin, _terminus);
        }
    }
}

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