C# Winform 点击通过

Question

Right now, I have a simple form window. It is used to display a picture.

When I hover over the picture in this window, I want to set its opacity to 50%, and at the same time, set the mouse to penetrate. In this way, you can see the desktop content behind the picture and can click on it.

Main method:

[DllImport("user32.dll")]
public static extern uint SetWindowLong(IntPtr h, int n, uint x);
    
void Update(){
    if (ishover)
    {
        Form.Opacity = 128;
        SetPenetrate(true);
    }
    else
    {
        Form.Opacity = 255,
        SetPenetrate(false);
    }
}

public void SetPenetrate(bool value)
{
    if (value)
    {
            SetWindowLong(this.Handle, -20, 0x20 | 0x80000);
    }
    else
    {
            this.FormBorderStyle = FormBorderStyle.None;
    }
}

In the code, when ishover, the setwindowlong method will be called, then the ishover will be false, and then it will be restored to unclickable. Then the hover will be detected again, and the loop will continue.

The solution currently in mind is to add a hook to determine whether the mouse is hovering in the current window, and then do the corresponding processing. Is there a more concise idea or api here?

Answer 1

Used System.Runtime.InteropServices

using System.Runtime.InteropServices;

namespace TransparentWindow
{
  public partial class Form1 : Form
  {
     #region

     //The SendMessage function sends a message to a window or windows.
     [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
     static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);

     //ReleaseCapture releases a mouse capture
     [DllImportAttribute("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]

     public static extern bool ReleaseCapture();
    
     #endregion

     public Form1()
     {
         InitializeComponent();
     }

     private void Form1_Load(object sender, EventArgs e)
     {
         this.BackColor = Color.Lime;
         this.TransparencyKey = Color.Lime;
     }

     private void Form1_MouseDown(object sender, MouseEventArgs e)
     {
         if (e.Button == MouseButtons.Left)
         {
             ReleaseCapture();
             SendMessage(this.Handle, 0xa1, 0x2, 0);
         }
     }
   }
}

You will get a Transparent form and you will be able to click through it.

Sample Output: