C# Signature:

[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

VB .Net Signature:

<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _
Public Shared Function SetParent(ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr
End Function

or

Declare Auto Function SetParent Lib "user32" (ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

Use this to create forms and then place child windows on it.

Sample Code C#:

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, int wParam, int lParam);

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

    [DllImport("user32.dll")]
    static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

    const int WM_SYSCOMMAND = 274;
    const int SC_MAXIMIZE = 61488;

    // add button & panel.
    // copy this into Button click event.

    Process proc = Process.Start(
    new ProcessStartInfo()
    {
        FileName = "cmd",
        Arguments = "/c echo hello user ^<!^> && pause",
        WindowStyle = ProcessWindowStyle.Minimized
    });
    Thread.Sleep(1000);
    //ShowWindow(proc.MainWindowHandle, 0);
    SetParent(proc.MainWindowHandle, this.panel1.Handle);
    //ShowWindow(proc.MainWindowHandle, 1);
    SendMessage(proc.MainWindowHandle, WM_SYSCOMMAND, SC_MAXIMIZE, 0);

    /*SetParent(FindWindow(vbnullstring,"notepad.exe"),me.handle)
    Me.SuspendLayout()
    Dim runProcess As New System.Diagnostics.Process
    Dim info As New System.Diagnostics.ProcessStartInfo
    info.FileName = "NotePad.exe"
    info.WindowStyle = ProcessWindowStyle.Normal
    runProcess = Process.Start(info)
    SetParent(runProcess.MainWindowHandle, Me.Handle)
    Me.ResumeLayout()*/

Sample Code C# 2:

// Runs notepad and places it's window into form.
using System.Diagnostics;
using System.Threading;
using System.Runtime.InteropServices;

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

     [DllImport("user32")]
     public static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

     private void button1_Click(object sender, EventArgs e)
     {
         var p = Process.Start(Environment.GetEnvironmentVariable("windir") + "\\notepad.exe");

         Thread.Sleep(100);

         SetParent(p.MainWindowHandle, this.Handle);
     }

     }
}

Sample Code VB.NET:

Imports System.Diagnostics
Imports System.Threading

Public Class Form1
     Declare Auto Function SetParent Lib "user32" (ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As IntPtr

     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
     Dim p = Process.Start(Environment.GetEnvironmentVariable("windir") + "\notepad.exe")

     Thread.Sleep(100)

     SetParent(p.MainWindowHandle, Me.Handle)
     End Sub
End Class

Alternative Managed API:

MDIParent and MDIChild do work for interforms.

One thing that makes SetParent more useful than MDIParent is that there are cases in which a control may be unstable in a MDI interface.

An example of this that I have encountered is using the FarPoint Spread 3.0/6.0 ActiveX controls. These controls will throw a Runtime protected memory violation exception if they are hosted in a WinForms Form, instantiated and then the Form.MDIParent property is set to an MDI container Form but using the SetParent(childForm.Handle, Me.Handle) call works.