Question

我想通过鼠标绘制一条线（交互式），我使用C＃和WinForm，该线应该在任何时候从起点（当鼠标按在面板上时）到鼠标的当前位置时出现比如在画图程序中画一条线。

但代码产生了很多行，我知道为什么，但我不知道如何克服这个问题

enter image description here

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;
    }

}}

任何帮助？我想绘制很多行并尽可能简化代码！

Answer 1

您需要更好地管理绘图。一些指示：

请勿使用CreateGraphics。相反，请使用控件已提供的Paint事件。
将您的绘图放在您自己的继承类中。除非您在表单上绘制，否则不要在Form类中绘图。

这是一个示例类。它继承自Panel。只需将其添加到表单中，例如在Form的构造函数中使用this.Controls.Add(new PanelWithMouseDraw());。
之类的内容
注意：这使用Tuple我认为需要.NET 4.0或更高版本。你可以用其他东西替换这个结构，如果需要的话......你只需要保留一个Point对列表。

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); } } }

Answer 2

简单修复，按如下方式更改方法panel1_MouseMove：

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);
        p = p2; // just add this

    }
}

请记住，这对任何鼠标按钮都有效，左或右无关紧要。

EDIT1：

这应画一条直线和之前的所有。

namespace WindowsFormsApplication2
{
public partial class Form1 : Form
{
    public struct Line
    {
        public Point start;
        public Point end;
    }

    public Form1()
    {
        InitializeComponent();
    }

    Pen erasePen = new Pen(Color.White, 3.0F);
    Pen myPen = new Pen(Color.Red, 3.0F);
    Point p = new Point();
    Point endPoint = new Point();
    bool flag = false;
    List<WindowsFormsApplication2.Form1.Line> lines = new List<WindowsFormsApplication2.Form1.Line>();


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

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

            Point p2 = e.Location;

            EraseLine(p, endPoint, g);

            DrawAllLines(lines, g);

            DrawLine(p, p2, g);

            endPoint = p2;

            g.Dispose();
        }
    }

    private void panel1_MouseUp(object sender, MouseEventArgs e)
    {
        // redraw for one last time...
        Graphics g = panel1.CreateGraphics();

        Point p2 = e.Location;

        lines.Add(new Line { start = p, end = p2} );

        EraseLine(p, endPoint, g);

        DrawAllLines(lines, g);

        flag = false;

        g.Dispose();
    }

    private void DrawLine(Point start, Point end, Graphics g)
    {
        g.DrawLine(myPen, start, end);
    }

    private void DrawLine(WindowsFormsApplication2.Form1.Line line, Graphics g)
    {
        g.DrawLine(myPen, line.start, line.end);
    }

    private void DrawAllLines(List<WindowsFormsApplication2.Form1.Line> allLines, Graphics g)
    {
        foreach(WindowsFormsApplication2.Form1.Line l in allLines)
        {
            g.DrawLine(myPen, l.start, l.end);
        }
    }

    private void EraseLine(Point start, Point end, Graphics g)
    {
        g.DrawLine(erasePen, start, end);
    }

}}

在面板中通过鼠标绘制线条

2 个答案: