Fade WS_EX_LAYERED form

Question

Fade WS_EX_LAYERED form

I have a form which I make click-through using the following function calls:

SetWindowLong(Handle, GWL_EXSTYLE, (IntPtr)(GetWindowLong(Handle, GWL_EXSTYLE) ^ WS_EX_LAYERED ^ WS_EX_TRANSPARENT));
SetLayeredWindowAttributes(Handle, 0, 0xFF, LWA_ALPHA);

This works fine, however when I try to fade that window using the System.Windows.Forms.Form.Opacity property I get the following exception:

System.ComponentModel.Win32Exception (0x80004005): The parameter is not valid
   at System.Windows.Forms.Form.UpdateLayered()
   at System.Windows.Forms.Form.set_Opacity(Double value)

How can I achieve both things at the same time?

c#

winforms

pinvoke

asked on Stack Overflow Dec 18, 2018 by

Jonas Kohl

1 Answer

The following works on a windows form

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace WindowsFormsApplication30
{
    public partial class Form1 : Form
    {

        [DllImport("user32.dll", SetLastError = true)]
        static extern System.UInt32 GetWindowLong(IntPtr hWnd, int nIndex);
        [DllImport("user32.dll", EntryPoint = "SetWindowLong")]
        private static extern int SetWindowLong32(IntPtr hWnd, int nIndex, uint dwNewLong);
        [DllImport("user32.dll", CharSet = CharSet.Ansi, SetLastError = true)]
        static extern int SetLayeredWindowAttributes(IntPtr hWnd, int crKey, byte bAlpha, uint dwFlags);



        public const int GWL_EXSTYLE = -20;
        public const uint WS_EX_LAYERED = 0x80000;
        public const uint LWA_ALPHA = 0x2;
        public const uint LWA_COLORKEY = 0x1;
        public Form1()
        {
            InitializeComponent();

            IntPtr Handle = this.Handle;
            UInt32 windowLong = GetWindowLong(Handle, GWL_EXSTYLE);
            SetWindowLong32(Handle, GWL_EXSTYLE, (uint)(windowLong ^ WS_EX_LAYERED));
            SetLayeredWindowAttributes(Handle, 0, 128, LWA_ALPHA);
        }
    }
}

answered on Stack Overflow Dec 18, 2018 by

jdweng

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