adding Transparent Form in Panel

Question

Hi ,

I had started a new project in which i am opening c# forms and closing many times . I searched and found many suggestion but my problem is somewhat different . I have a single page in my project . and had to provide some space in it to show the closing and opening of forms . So I decided to introduce a panel in it and used to show forms in there . all is going well untill a problem came . i had to do the below
https://stackoverflow.com/questions/34947504/how-to-show-a-pop-up-message-with-dark-background?noredirect=1&lq=1

(add a dark blackground form before opening a form which have something to be in focus . )

before moving forward I must tell you why i choose panel . because by using panel , the form would stick inside the bounds of panel so that whenever i panel moves so as the form inside it . but ...

now the worst problem came when i came to know that transaprent/opaque forms cannot be added to the panel . It just shattered every logic of my project as i was stuck and found absolutely no solution whatso ever in any form .

Now here in this forum , i found some comments that say that for this opening and closing of forms ,a separte technique has to be used like creating a user control but i found no reference of this (creation of user control ) in their comments . They didn't say why and how the problem would be solved . So i am requesting any expert here to please help by creating a basic model for this .

Answer 1

If the OS is Windows 8 or higher, you can make the child window a layered window. To do this, add an application manifest and enable Windows 8.

<!-- Windows 8 -->
<supportedOS Id="{4a2f28e3-53b9-4441-ba9c-d69d4a4a6e38}" />

Create a class that inherits UserControl.

using System;
using System.ComponentModel;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

public class LayerdUserControl : UserControl
{
    private Color _TransparencyKey = Color.Empty;
    private double _Opacity = 1.0f;

    protected override void OnHandleCreated(EventArgs e) {
        base.OnHandleCreated(e);
        var dwStyle = GetWindowLong(Handle, GWL_EXSTYLE);
        dwStyle |= WS_EX_LAYERED;
        SetWindowLong(Handle, GWL_EXSTYLE, dwStyle);
        UpdateLayered();
        BeginInvoke(new MethodInvoker(InvalidateChildren));
    }

    protected override void OnInvalidated(InvalidateEventArgs e) {
        base.OnInvalidated(e);
        InvalidateChildren();
    }

    protected virtual void InvalidateChildren() {
        if (HasChildren) {
            foreach (Control con in Controls) {
                con.Invalidate(true);
            }
        }
    }

    private void UpdateLayered() {
        if (DesignMode || !IsHandleCreated) {
            return;
        }

        Color transparencyKey = TransparencyKey;
        byte opacityAsByte = (byte)(Opacity * 255.0f);
        bool result;
        if (transparencyKey.IsEmpty) {
            result = SetLayeredWindowAttributes(Handle, 0, opacityAsByte, LWA_ALPHA);
        } else if (opacityAsByte == 255) {
            result = SetLayeredWindowAttributes(Handle, ColorTranslator.ToWin32(transparencyKey), 0, LWA_COLORKEY);
        } else {
            result = SetLayeredWindowAttributes(Handle, ColorTranslator.ToWin32(transparencyKey),
                                                        opacityAsByte, LWA_ALPHA | LWA_COLORKEY);
        }
        if (!result) {
            throw new Win32Exception();
        }
    }

    [Category("LayerdWindow")]
    public virtual Color TransparencyKey {
        get {
            return _TransparencyKey;
        }
        set {
            if (_TransparencyKey != value) {
                _TransparencyKey = value;
                UpdateLayered();
            }
        }
    }

    protected virtual void ResetTransparencyKey() {
        TransparencyKey = Color.Empty;
    }

    protected virtual bool ShouldSerializeTransparencyKey() {
        return !_TransparencyKey.IsEmpty;
    }

    [Category("LayerdWindow")]
    [DefaultValue(1.0)]
    [TypeConverterAttribute(typeof(OpacityConverter))]
    public virtual double Opacity {
        get {
            return _Opacity;
        }
        set {
            if (_Opacity != value) {
                _Opacity = value;
                UpdateLayered();
            }
        }
    }

    private const int WS_EX_LAYERED = 0x80000;
    private const int GWL_EXSTYLE = -20;
    private const int LWA_COLORKEY = 1;
    private const int LWA_ALPHA = 2;

    [DllImport("user32.dll", SetLastError = true)]
    private static extern int GetWindowLong(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern bool SetLayeredWindowAttributes(IntPtr hwnd, int crKey, byte bAlpha, int dwFlags);
}

How To Use:

public partial class Form1 : Form
{
    public Form1() {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e) {
        var f = new LayerdUserControl();
        f.Text = string.Empty;
        f.Opacity = 0.5;
        f.BackColor = Color.Black;
        f.Dock = DockStyle.Fill;
        Controls.Add(f); 
        f.Show();
        f.BringToFront();
    }
}