c# - 当位置从左上角移动到初始位置时，如何在 C# 中绘制框？

Question

所以我试图让用户在表单上绘制框，当我从左上角到右下角绘制时一切顺利。一旦 X 或 Y 位置变得小于原始位置，它就会停止绘制并且矩形消失。

我对 paint 方法进行了一些更改，以尝试调整其位置并将其移动到应该模拟此行为的位置，但它无法正常工作。有没有更好的方法来解决这个问题？我可以在屏幕上获得多个矩形，甚至可以双击以检测并删除它们。除了右下角，我无法让他们朝任何其他方向绘制

    // All rectangles saved to the form
    private List<Rectangle> rects;

    // Current rectangle if one is being drawn
    private Rectangle tempRect;

    public Form1()
    {
        InitializeComponent();
        rects = new List<Rectangle>();
    }

    private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        tempRect = new Rectangle(e.X, e.Y, 0, 0);
        this.Invalidate();
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.Button == MouseButtons.Left)
        {
            int tempX = tempRect.X;
            int tempY = tempRect.Y;
            int tempWidth = tempRect.Width;
            int tempHeight = tempRect.Height;

            if (e.X < tempRect.Location.X)
            {
                tempX = e.X;
                tempWidth = tempRect.Width + (tempRect.Location.X - e.X);
            }
            else
                tempWidth = e.X - tempRect.Location.X;

            if (e.Y < tempRect.Location.Y)
            {
                tempY = e.Y;
                tempHeight = tempRect.Height + (tempRect.Location.Y - e.Y);
            }
            else
                tempHeight = e.Y - tempRect.Location.Y;

            Point rectLocation = new Point(tempX, tempY);
            Size rectSize = new Size(tempWidth, tempHeight);

            tempRect = new Rectangle(rectLocation, rectSize);
            this.Invalidate();
        }
    }

    private void Form1_MouseUp(object sender, MouseEventArgs e)
    {
        // Must be within constraint, prevents tiny invisible rectangles from being added
        if (tempRect.Width >= 10 && tempRect.Height >= 10)
            rects.Add(tempRect);
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        using (Pen pen = new Pen(Color.Black, 2))
        {
            // Redraws all existing rectangles onto the form
            foreach (Rectangle rect in rects)
                e.Graphics.DrawRectangle(pen, rect);

            // Must be within constraint, prevents tiny invisible rectangles from being added
            if (tempRect.Width >= 10 && tempRect.Height >= 10)
                e.Graphics.DrawRectangle(pen, tempRect);
        }
    }

Answer 1

您可以显着简化您的代码。您可以创建 tempStartPoint，而不是在鼠标按下时创建 tempRect。这样，您就不需要在 MouseMove 事件处理程序中进行那么多操作，所有代码都将归结为一条语句:

tempRect =
    new Rectangle(
        Math.Min(tempStartPoint.X, tempEndPoint.X),
        Math.Min(tempStartPoint.Y, tempEndPoint.Y),
        Math.Abs(tempStartPoint.X - tempEndPoint.X),
        Math.Abs(tempStartPoint.Y - tempEndPoint.Y));

完整代码:

public partial class Form1 : Form
{
    private readonly List<Rectangle> rects = new List<Rectangle>();
    private Point tempStartPoint;
    private Rectangle tempRect;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        tempStartPoint = e.Location;
        Invalidate();
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.Button != MouseButtons.Left)
            return;
        Point tempEndPoint = e.Location;
        tempRect =
            new Rectangle(
                Math.Min(tempStartPoint.X, tempEndPoint.X),
                Math.Min(tempStartPoint.Y, tempEndPoint.Y),
                Math.Abs(tempStartPoint.X - tempEndPoint.X),
                Math.Abs(tempStartPoint.Y - tempEndPoint.Y));
        Invalidate();
    }

    private void Form1_MouseUp(object sender, MouseEventArgs e)
    {
        // Must be within constraint, prevents tiny invisible rectangles from being added
        if (tempRect.Width >= 10 && tempRect.Height >= 10)
            rects.Add(tempRect);
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        using (Pen pen = new Pen(Color.Black, 2))
        {
            // Redraws all existing rectangles onto the form
            foreach (Rectangle rect in rects)
                e.Graphics.DrawRectangle(pen, rect);

            // Must be within constraint, prevents tiny invisible rectangles from being added
            if (tempRect.Width >= 10 && tempRect.Height >= 10)
                e.Graphics.DrawRectangle(pen, tempRect);
        }
    }
}