尝试用C#形式设计Square的预览

Question

我试图通过在单击时拖动鼠标来创建一个正方形，我可以单独创建正方形，但无法使其与预览一起使用。拖动时，预览形状由于某种原因不会被删除，我不太明白为什么会发生这种情况。我将包含发生这种情况的图片和视频，因为很难用文字解释它。

预览如何工作：有 2 支笔，一支用于擦除正在创建的形状，同时光标在表单中移动，直到松开并设计出正方形

public partial class Form1 : Form
{
    Pen pen, eraser;
    Graphics graphics;
    Bitmap bitmap;
    Point startPoint, endPoint;
    int choice;
    Boolean draw;
    int width;
    int height;
    public Form1()
    {
        InitializeComponent();
    }

    private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
    {
        if (draw && choice == 1)
        {
            width = e.Location.X - startPoint.X;
            height = e.Location.Y - startPoint.Y;
            width = height;
            Rectangle shape = new Rectangle(startPoint.X, startPoint.Y, width, height);
            graphics.DrawRectangle(pen, shape);
            pictureBox1.Refresh();
            draw = false;
        }
    }

    private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
    {
        if (draw && choice == 1)
        {
            width = e.Location.X - startPoint.X;
            height = e.Location.Y - startPoint.Y;
            width = height;
            graphics.DrawRectangle(eraser, startPoint.X, startPoint.Y, width, height);
            graphics.DrawRectangle(pen, startPoint.X, startPoint.Y, width, height);
            pictureBox1.Refresh();
        }
    }



    private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
    {
        startPoint = e.Location;
        draw = true;
    }

Answer 1

您的问题可能与您的想法相反。您之前绘制的任何正方形都应该自动擦除，直到您需要将其保存在某种文档中（请参见下面的

Squares

），以便将多个形状放在一起。

class PictureBoxEx : PictureBox
{
    protected override void OnMouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);
        _mouseDownPoint = e.Location;
    }
    Point _mouseDownPoint = default;

    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);
        _mouseCurrentPoint = e.Location;
        if (MouseButtons == MouseButtons.Left)
        {
            BeginInvoke((MethodInvoker)delegate { Invalidate(); });
        }
    }
    Point _mouseCurrentPoint = default;
    protected override void OnMouseUp(MouseEventArgs e)
    {
        base.OnMouseUp(e);
        Squares.Add(_currentSquare);
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        if(MouseButtons == MouseButtons.Left) 
        {
            var delta = _mouseCurrentPoint.Y - _mouseDownPoint.Y;
            using (var pen = new Pen(Color.DarkRed, 2F))
            {
                Debug.WriteLine($"{_mouseDownPoint}{_mouseCurrentPoint}");
                var width = _mouseCurrentPoint.X - _mouseDownPoint.X;
                var height = _mouseCurrentPoint.Y - _mouseDownPoint.Y;
                var side = Math.Max(width, height);
                _currentSquare = new Rectangle(_mouseDownPoint, new Size(side, side));
                e.Graphics.DrawRectangle(pen, _currentSquare);
                
                // Comment this out to keep just the current square.
                foreach (var square in Squares)
                {
                    e.Graphics.DrawRectangle(pen, square);
                }
            }
        }
    }
    Rectangle _currentSquare = default;
    List<Rectangle> Squares { get; } = new List<Rectangle>();
}