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Open ChildForm with owner permission

I am trying to insert a form inside another form. I used .Controls.Add(form) and it works. My problem is that I have to declare the owner and to do that I have to set the toplevel to true but if I set the toplevel to true I get stuck with the control.add bacause telling me that it is impossible to add a top level control to a control.
How can I do?
public void openChildForm(Form childForm)
{
if (activeForm != null) activeForm.Close();
activeForm = childForm;
childForm.TopLevel = true;
childForm.TopMost = true;
childForm.FormBorderStyle = FormBorderStyle.None;
childForm.Dock = DockStyle.Fill;
this.Controls.Add(childForm);
panelChildForm.Tag = childForm;
childForm.Owner = this;
childForm.BringToFront();
childForm.Show();
}
thankyou in advance,
Davide.

For me it's a bit strange what you are trying to do. A form is kind of window. Why would you add a window in another window? Don't you want to create a user control and to display that user control in your existing form?

There isn't enough information to go on from the original question you've posted, but it looks like you're trying to create the kind of functionality that a sidebar page menu might offer. In that situation, clicking on a button on the sidebar changes the window that's currently being displayed. Perhaps this question about sidebar navigation would relate to what you're saying? There's some information also available if you try searching "winforms sidebar navigation," such as this post about creating navigation in winforms, and there are a lot more linked from this question.
I'm just taking a guess at what you're trying to do here. Perhaps if you want to refine the answers you're getting, the original question should include a link to a github sample project, or at least a bit more of an explanation of what the target is.

It looks like you are working with WinForms.
Look at MDI Forms (Multiple-Document Interface Forms)
You can handle this by setting the parent form property IsMdiContainer = true
and then the child form childForm.MdiParent = parentForm;.
Here is a small example:
Add a menuStrip to the parentForm and set the parent form MainMenuStrip = menuStrip. Add a menu item and add some code to the menuStrip_ItemClicked event.
private void menuStrip_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
{
if (e.ClickedItem.Text == "New Child")
ShowNewForm(sender, e);
}
private void ShowNewForm(object sender, EventArgs e)
{
Form childForm = new Form();
childForm.MdiParent = this;
childForm.Text = "Window " + childFormNumber++;
childForm.Show();
}
You should end up with this behaviour.
If you want to access other forms within the same application you can use a loop and find a form using Application.OpenForms or find a form using either Application.OpenForms["form1"] or Application.OpenForms[0]
If you use MdiForms you can find child forms using parentMdiForm.MdiChildren

How to add a form inside a specific layout?

I am not that PRO using WindowsForms because I do not use them too much but right now I am developing a Inventory system so this is my approach(design):
I have used 3 FlowLayoutPanels, I am trying to show various Forms inside FlowLayoutPanel3 when clicking specific button in the left panel the flowlayoutpanel3 will show/trigger the specific form.
What I have tried?, well I have read that I can use MDI container and stuff like that but I noticed that it is a different approach because I do not want to show a separate window, just just inside the flowlayoutpanel3 and maximized.
I have been googling solutions but could not find a solution. * OR is there any item in the toolbox to perform this kind of stuff?*
PD: I am using VS2019 and C#.

Create the new form, set it's TopLevel to false, add it to the panel controls and maximize it:
var frm = new Form(); //Or whatever form type you want to use.
frm.TopLevel = false;
frm.FormBorderStyle = FormBorderStyle.None;
flowLayoutPanel3.Controls.Add(frm);
frm.WindowState = FormWindowState.Maximized;
You may need also to make it visible
frm.Visible = true;

How to create a windows form that replaces the current form?

I am making a game using Windows Forms, and I feel that the easiest way to make different screens (Main Menu, Settings, Etc...) is using a separate form for each screen. I have looked up up many different ways to do this. Many people talk of using form2.Show(); this.Hide();, however, this creates a new popup window.
People have also suggested using this.IsMdiContainer = true; to create a new window inside of the current window, but this is also not the functionality I want.
EDIT: Another question, multiple-guis-one-window, explains slightly that this can be achieved using UserControls, but does not elaborate with any examples, or what I should do.
I want to completely replace the current form's functionality with that of a new form.
Is there a way to achieve this? If not, is there a good alternative?

As I understood, you want to keep the same form and change the data inside that form (to not get the effect that your form was closed and reopened again).
The problem is windows form does not support such thing directly (at least not in an optimal way), I would use another UI frameworks for that. However, if you want to stick though with windows forms, you may use GroupBox or Panel tools (available from windows form design tools in Visual studio). Here you can group your elements as required, and show/hide the group/panel as required.
That is one of the best available solution for windows form AFAIK.

You want to open child forms within main form then you should try this i have create it without any User Control.
I have manage one parent form and two child forms. child forms should be open within parent form.
frmMain(Parent Form)
Set frmMain Property as Following
WindowState = System.Windows.Forms.FormWindowState.Maximized
I have take 3 panel in frmMain window.
pnlMenu (For Display Menu)
Set pnlMenu.Dock = System.Windows.Forms.DockStyle.Top property
Set height of this panel as you require.
pnlMain (For Display Child Forms)
Set pnlMain.Dock = System.Windows.Forms.DockStyle.Fill property
pnlFooter (For Footer Section)
Set pnlFooter.Dock = System.Windows.Forms.DockStyle.Bottom; property
Set height of this panel as you require.
I have set menubar in pnlMenu(Click on that menu for display child form in pnlMain)
frmMain.cs
public void BindFormIntoMainForm(Form Main)
{
Main.TopLevel = false;
Main.WindowState = FormWindowState.Maximized;
Main.AutoScroll = true;
pnlMain.Controls.Clear();
pnlMain.Controls.Add(Main);
pnlMain.Refresh();
Main.Show();
}
private void childToolStripMenuItem_Click(object sender, EventArgs e)
{
frmChildForm1 ChildForm1 = new frmChildForm1();
BindFormIntoMainForm(ChildForm1);
}
private void childForm2ToolStripMenuItem1_Click(object sender, EventArgs e)
{
frmChildForm2 ChildForm2 = new frmChildForm2();
BindFormIntoMainForm(ChildForm2);
}
BindFormIntoMainForm method responsible for display child form in main window.
frmChildForm1 & frmChildForm2(ChildForm)
Set both form Property as Following
FormBorderStyle = System.Windows.Forms.FormBorderStyle.None
Now when you click on Child Form 1 Menu then display following output:
when you click on Child Form 2 Menu then display following output:
I think it can be helpful for you.

How can I add wpf form inside windows forms tabpage?

When clicked show button I show win form inside tabcontrol which elements of win form, but I can not add wpf form inside this tabcontrol;
Faturalar() is the win forms;
Fatura.Faturalar ftr = new Fatura.Faturalar();
ftr.TopLevel = false;
ftr.Visible = true;
ftr.FormBorderStyle = FormBorderStyle.None;
ftr.Dock = DockStyle.Fill;
tabControl1.TabPages[0].Controls.Add(ftr);
it works but;
MainWindow is wpf forms;
MenuYonetimi.MainWindow mny = new MenuYonetimi.MainWindow();
tabControl1.TabPages[2].Controls.Add(mny);
it doesn't allow to do

Top-level Windows cannot be contained inside other Windows or "form"s if you want to call it that. If you need WPF content inside a winforms app you will need to place an ElementHost inside the form and place your WPF UI (probably in a WPF UserControl). But there's no way that any form or window will contain another Window.

Embed a form onto a tabcontrol in windows forms

I have a tab control in a windows form and I want to be able to click on a tab and in the body area of the tab I want it to display another form as an embedded component. Is this possible? If so, can someone please provide an example or a link to an example of how to accomplish this?

You are probably looking for Tabbed MDI Child Forms

You can embed a Form but it's not the best choice.
Better place the contents on UserControls and add that to the TabPage.

Set your MainForm (Parent) as IsMDIContainer = true;
Create an instance of the ChildForm and call this function:
FormChild frmChild = new FormChild();
AddNewTab(frmChild);
Copy this Function to your code:
private void AddNewTab(Form frm)
{
TabPage tab = new TabPage(frm.Text);
frm.TopLevel = false;
frm.Parent = tab;
frm.Visible = true;
tabControl.TabPages.Add(tab);
frm.Location = new Point((tab.Width - frm.Width) / 2, (tab.Height - frm.Height) / 2);
tabControl.SelectedTab = tab;
}

I think the other answer has the right idea; Tabbed MDI is probably what you want.
There is an approach where you create a UserControl that has the same content as the form and use that on the TabPage.
TabPage myTabPage = new TabPage(sometext);
myUserControl = new myUserControlType();
myUserControl.Dock = DockStyle.Fill;
myTabPage.Controls.Add(myUserControl);
myTabControl.Add(myTabPage);
http://bytes.com/topic/c-sharp/answers/270457-can-i-add-form-tabpage goes into more detail; but I'd look at the MDI stuff first.

If you do not want to use MDI, you can try to put everything from desired form to user control and add this user control in both form and tab.