C# 为什么'；What’用鼠标在新的透明窗体上画一个矩形不是吗？

它将进入

F_Paint

事件，但不会进入

F_MouseDown

事件。 我希望能够在

F

窗体上绘制矩形

也许因为

F

表单是透明的，所以它不能在上面绘制？但是它永远不会到达

F_MouseDown

事件，我在

F_MouseDown

事件中使用了一个断点

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Tester
{
    public partial class Form1 : Form
    {
        Ffmpeg ffmpeg = new Ffmpeg();

        private bool _canDraw;
        private int _startX, _startY;
        private Rectangle _rect;

        public Form1()
        {
            InitializeComponent();

            BackColor = Color.Blue;
            TransparencyKey = BackColor;
            Opacity = 1;
            var f = new HelperForm { Opacity = 0, ShowInTaskbar = false, FormBorderStyle = FormBorderStyle.None };
            f.MouseDown += F_MouseDown;
            f.MouseMove += F_MouseMove;
            f.MouseUp += F_MouseUp;
            f.Paint += F_Paint;
            f.Show();
            Visible = false;
            Owner = f;
            Visible = true;
            Move += (o, a) => f.Bounds = Bounds;
            Resize += (o, a) => f.Bounds = Bounds;
            f.Bounds = Bounds;
            ffmpeg.Start(@"d:\ffmpegx86\test.mp4", 24);
        }

        private void F_Paint(object sender, PaintEventArgs e)
        {
            //Create a new 'pen' to draw our rectangle with, give it the color red and a width of 2
            using (Pen pen = new Pen(Color.Red, 2))
            {
                //Draw the rectangle on our form with the pen
                e.Graphics.DrawRectangle(pen, _rect);
            }
        }

        private void F_MouseUp(object sender, MouseEventArgs e)
        {
            //The system is no longer allowed to draw rectangles
            _canDraw = false;
        }

        private void F_MouseMove(object sender, MouseEventArgs e)
        {
            //If we are not allowed to draw, simply return and disregard the rest of the code
            if (!_canDraw) return;

            //The x-value of our rectangle should be the minimum between the start x-value and the current x-position
            int x = Math.Min(_startX, e.X);
            //The y-value of our rectangle should also be the minimum between the start y-value and current y-value
            int y = Math.Min(_startY, e.Y);

            //The width of our rectangle should be the maximum between the start x-position and current x-position minus
            //the minimum of start x-position and current x-position
            int width = Math.Max(_startX, e.X) - Math.Min(_startX, e.X);

            //For the hight value, it's basically the same thing as above, but now with the y-values:
            int height = Math.Max(_startY, e.Y) - Math.Min(_startY, e.Y);
            _rect = new Rectangle(x, y, width, height);
            //Refresh the form and draw the rectangle
            Refresh();
        }

        private void F_MouseDown(object sender, MouseEventArgs e)
        {
            //The system is now allowed to draw rectangles
            _canDraw = true;
            //Initialize and keep track of the start position
            _startX = e.X;
            _startY = e.Y;
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            ffmpeg.Close();
        }
    }

    class HelperForm : Form
    {
        protected override CreateParams CreateParams
        {
            get
            {
                const int WS_EX_TOOLWINDOW = 0x80;
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= WS_EX_TOOLWINDOW;
                return cp;
            }
        }
    }
}

不确定它为什么没有进入

MouseDown

事件

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Tester
{
    public partial class Form1 : Form
    {
        Ffmpeg ffmpeg = new Ffmpeg();

        private bool _canDraw;
        private int _startX, _startY;
        private Rectangle _rect;

        public Form1()
        {
            InitializeComponent();

            BackColor = Color.Blue;
            TransparencyKey = BackColor;
            Opacity = 1;
            var f = new HelperForm { Opacity = 0, ShowInTaskbar = false, FormBorderStyle = FormBorderStyle.None };
            f.MouseDown += F_MouseDown;
            f.MouseMove += F_MouseMove;
            f.MouseUp += F_MouseUp;
            f.Paint += F_Paint;
            f.Show();
            Visible = false;
            Owner = f;
            Visible = true;
            Move += (o, a) => f.Bounds = Bounds;
            Resize += (o, a) => f.Bounds = Bounds;
            f.Bounds = Bounds;
            ffmpeg.Start(@"d:\ffmpegx86\test.mp4", 24);
        }

        private void F_Paint(object sender, PaintEventArgs e)
        {
            //Create a new 'pen' to draw our rectangle with, give it the color red and a width of 2
            using (Pen pen = new Pen(Color.Red, 2))
            {
                //Draw the rectangle on our form with the pen
                e.Graphics.DrawRectangle(pen, _rect);
            }
        }

        private void F_MouseUp(object sender, MouseEventArgs e)
        {
            //The system is no longer allowed to draw rectangles
            _canDraw = false;
        }

        private void F_MouseMove(object sender, MouseEventArgs e)
        {
            //If we are not allowed to draw, simply return and disregard the rest of the code
            if (!_canDraw) return;

            //The x-value of our rectangle should be the minimum between the start x-value and the current x-position
            int x = Math.Min(_startX, e.X);
            //The y-value of our rectangle should also be the minimum between the start y-value and current y-value
            int y = Math.Min(_startY, e.Y);

            //The width of our rectangle should be the maximum between the start x-position and current x-position minus
            //the minimum of start x-position and current x-position
            int width = Math.Max(_startX, e.X) - Math.Min(_startX, e.X);

            //For the hight value, it's basically the same thing as above, but now with the y-values:
            int height = Math.Max(_startY, e.Y) - Math.Min(_startY, e.Y);
            _rect = new Rectangle(x, y, width, height);
            //Refresh the form and draw the rectangle
            Refresh();
        }

        private void F_MouseDown(object sender, MouseEventArgs e)
        {
            //The system is now allowed to draw rectangles
            _canDraw = true;
            //Initialize and keep track of the start position
            _startX = e.X;
            _startY = e.Y;
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            ffmpeg.Close();
        }
    }

    class HelperForm : Form
    {
        protected override CreateParams CreateParams
        {
            get
            {
                const int WS_EX_TOOLWINDOW = 0x80;
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= WS_EX_TOOLWINDOW;
                return cp;
            }
        }
    }
}

---

有几个原因阻止绘制矩形并触发鼠标事件。首先，将

不透明度设置为
0
；这意味着你试图画的东西永远都看不见。相反，您应该将
透明键
设置为
背景色中的颜色
：

f.TransparencyKey = f.BackColor;

然后，您尝试使用从未初始化过的对象
\rect
绘制一个矩形；因此，您试图绘制的矩形将以0宽0高的大小绘制，这意味着不会绘制该矩形，因此，在初始化过程中，您应该为
\u rect
提供默认值，例如：

_rect = new Rectangle(Point.Empty, this.Size);

绘制的矩形现在应该是可见的；但是，事件不会触发，因为您正在反转表单所有权，因此

Owner = f;

使用：

因为您正在将
不透明度设置为
0
。