问题是，宿主（重定父级）窗口在激活时不会导致宿主窗体也激活，因此它被带到前台。
宿主Window并不完全是子Window，宿主窗体不接收来自它的任何消息。
一种可能的方法，用于在此窗口获得焦点（单击或以其他方式激活它）时，将承载 foreign 窗口的窗体置于前台
它使用SetWinEventHook来安装一个Hook，该Hook监视窗口（EVENT_SYSTEM_FOREGROUND）的放置状态的变化。
您可以指定兴趣窗口的句柄（此处为您的proc.MainWindowHandle）及其ProcessId和ThreadId。请注意，它们与您的应用不同，需要调用GetWindowThreadProcessId()才能获取此信息。
当您激活 foreign 窗口时，挂钩调用指定的回调委托（此处为ForegrundChangedEventDelegate），该委托又执行它所指向的方法（ForegroundStateChangedCallback）
当调用此方法时，它会检查引起通知的对象是否为OBJID_WINDOW，以及事件是否实际为EVENT_SYSTEM_FOREGROUND。如果是，它会调用SetWindowPos，将宿主窗体置于前台，但不激活它，这样宿主窗口就不会失去焦点
备注：

• SetWinEvetHook委派会在父Form的建构函式（Sub New()）中建立，沿着使用GC SafeHandle来防止委派在错误的时间遭到内存回收。

它在OnHandleDestroyed()覆盖中释放，其中钩子proc也被解除钩子

• 请参阅以下表单中的imports语句：

Imports [Your App Namespace].NativeMethods

这意味着您必须指定应用程序的namespace，以便导入按预期工作。在VB .NET中，通常应用程序的名称与其主NameSpace匹配;如果您的应用命名为WinFormsApp1，则其Imports WinFormsApp1.NativeMethods

• 要激活钩子，只要你改变了那个窗口的父窗口，就用它的句柄调用SetForegroundStateChangedHook()方法。

当窗体关闭时，挂钩被释放
我建议使用Unhook Window into its original State中的代码来设置Parent（并且，可能的话，在关闭宿主窗体之前将其设置回原始值）。如果需要，您可以将WM_CLOSE发送到Window。

Imports [Your App Namespace].NativeMethods

Public Class SomeForm

    Private hForegrundChangedEventHook As IntPtr
    Private ReadOnly ForegrundChangedEventDelegate As WinEventDelegate
    Private Shared GCForegroundStateSafetyHandle As GCHandle

    Public Sub New()
        InitializeComponent()
        ForegrundChangedEventDelegate = New WinEventDelegate(AddressOf ForegroundStateChangedCallback)
        GCForegroundStateSafetyHandle = GCHandle.Alloc(ForegrundChangedEventDelegate)
    End Sub

    Protected Overrides Sub OnHandleDestroyed(e As EventArgs)
        GCForegroundStateSafetyHandle.Free()
        UnhookWinEvent(hForegrundChangedEventHook)
        MyBase.OnHandleDestroyed(e)
    End Sub

    Private Sub SetForegroundStateChangedHook(hWnd As IntPtr)
        Dim processId As UInteger
        Dim targetThreadId = GetWindowThread(hWnd, processId)
        hForegrundChangedEventHook = WinEventHookOne(SWEH_Events.EVENT_SYSTEM_FOREGROUND, ForegrundChangedEventDelegate, processId, targetThreadId)
    End Sub

    Friend Sub ForegroundStateChangedCallback(hWinEventHook As IntPtr, eventType As SWEH_Events, hWnd As IntPtr, idObject As SWEH_ObjectId, idChild As Long, dwEventThread As UInteger, dwmsEventTime As UInteger)
        If idObject = SWEH_ObjectId.OBJID_WINDOW AndAlso eventType = SWEH_Events.EVENT_SYSTEM_FOREGROUND Then
            Dim flags = SWP_Flags.SWP_ASYNCWINDOWPOS Or SWP_Flags.SWP_NOACTIVATE Or SWP_Flags.SWP_NOSIZE Or SWP_Flags.SWP_NOMOVE
            SetWindowPos(Handle, IntPtr.Zero, 0, 0, 0, 0, flags)
        End If
    End Sub
End Class

本机方法类

将此类添加到项目中，并按所述导入到窗体中

Imports System.Runtime.InteropServices

Public Class NativeMethods

    <DllImport("user32.dll", SetLastError:=True)>
    Friend Shared Function GetWindowThreadProcessId(hWnd As IntPtr, ByRef lpdwProcessId As UInteger) As UInteger
    End Function

    <DllImport("user32.dll", SetLastError:=True)>
    Friend Shared Function SetWindowPos(hWnd As IntPtr, hWndInsertAfter As IntPtr, x As Integer, y As Integer, cx As Integer, cy As Integer, uFlags As SWP_Flags) As Boolean
    End Function

    Friend Delegate Sub WinEventDelegate(
        hWinEventHook As IntPtr,
        eventType As SWEH_Events,
        hwnd As IntPtr, idObject As SWEH_ObjectId,
        idChild As Long,
        dwEventThread As UInteger,
        dwmsEventTime As UInteger)

    <DllImport("user32.dll", SetLastError:=False)>
    Friend Shared Function SetWinEventHook(
        eventMin As SWEH_Events,
        eventMax As SWEH_Events,
        hmodWinEventProc As IntPtr,
        lpfnWinEventProc As WinEventDelegate,
        idProcess As UInteger,
        idThread As UInteger,
        dwFlags As SWEH_dwFlags) As IntPtr
    End Function

    <DllImport("user32.dll", SetLastError:=False)>
    Friend Shared Function UnhookWinEvent(hWinEventHook As IntPtr) As Boolean
    End Function

    Friend Shared WinEventHookInternalFlags As SWEH_dwFlags =
        SWEH_dwFlags.WINEVENT_OUTOFCONTEXT Or SWEH_dwFlags.WINEVENT_SKIPOWNPROCESS

    Friend Shared Function WinEventHookOne(evt As SWEH_Events, weDelegate As WinEventDelegate, idProcess As UInteger, idThread As UInteger) As IntPtr
        Return SetWinEventHook(evt, evt, IntPtr.Zero, weDelegate, idProcess, idThread, WinEventHookInternalFlags)
    End Function

    Friend Shared Function GetWindowThread(hWnd As IntPtr, ByRef processID As UInteger) As UInteger
    #If NETFX Then
        new UIPermission(UIPermissionWindow.AllWindows).Demand();
    #End If
        processID = 0
        Return GetWindowThreadProcessId(hWnd, processID)
    End Function

    ' SetWinEventHook Events
    Friend Enum SWEH_Events As UInteger
        EVENT_MIN = &H1
        EVENT_MAX = &H7FFFFFFF
        EVENT_SYSTEM_SOUND = &H1
        EVENT_SYSTEM_ALERT = &H2
        EVENT_SYSTEM_FOREGROUND = &H3
        EVENT_SYSTEM_MENUSTART = &H4
        EVENT_SYSTEM_MENUEND = &H5
        EVENT_SYSTEM_MENUPOPUPSTART = &H6
        EVENT_SYSTEM_MENUPOPUPEND = &H7
        EVENT_SYSTEM_CAPTURESTART = &H8
        EVENT_SYSTEM_CAPTUREEND = &H9
        EVENT_SYSTEM_MOVESIZESTART = &HA
        EVENT_SYSTEM_MOVESIZEEND = &HB
        EVENT_SYSTEM_CONTEXTHELPSTART = &HC
        EVENT_SYSTEM_CONTEXTHELPEND = &HD
        EVENT_SYSTEM_DRAGDROPSTART = &HE
        EVENT_SYSTEM_DRAGDROPEND = &HF
        EVENT_SYSTEM_DIALOGSTART = &H10
        EVENT_SYSTEM_DIALOGEND = &H11
        EVENT_SYSTEM_SCROLLINGSTART = &H12
        EVENT_SYSTEM_SCROLLINGEND = &H13
        EVENT_SYSTEM_SWITCHSTART = &H14
        EVENT_SYSTEM_SWITCHEND = &H15
        EVENT_SYSTEM_MINIMIZESTART = &H16
        EVENT_SYSTEM_MINIMIZEEND = &H17
        EVENT_SYSTEM_DESKTOPSWITCH = &H20
        EVENT_SYSTEM_END = &HFF
        EVENT_OEM_DEFINED_START = &H101
        EVENT_OEM_DEFINED_END = &H1FF
        EVENT_UIA_EVENTID_START = &H4E00
        EVENT_UIA_EVENTID_END = &H4EFF
        EVENT_UIA_PROPID_START = &H7500
        EVENT_UIA_PROPID_END = &H75FF
        EVENT_CONSOLE_CARET = &H4001
        EVENT_CONSOLE_UPDATE_REGION = &H4002
        EVENT_CONSOLE_UPDATE_SIMPLE = &H4003
        EVENT_CONSOLE_UPDATE_SCROLL = &H4004
        EVENT_CONSOLE_LAYOUT = &H4005
        EVENT_CONSOLE_START_APPLICATION = &H4006
        EVENT_CONSOLE_END_APPLICATION = &H4007
        EVENT_CONSOLE_END = &H40FF
        EVENT_OBJECT_CREATE = &H8000
        EVENT_OBJECT_DESTROY = &H8001
        EVENT_OBJECT_SHOW = &H8002
        EVENT_OBJECT_HIDE = &H8003
        EVENT_OBJECT_REORDER = &H8004
        EVENT_OBJECT_FOCUS = &H8005
        EVENT_OBJECT_SELECTION = &H8006
        EVENT_OBJECT_SELECTIONADD = &H8007
        EVENT_OBJECT_SELECTIONREMOVE = &H8008
        EVENT_OBJECT_SELECTIONWITHIN = &H8009
        EVENT_OBJECT_STATECHANGE = &H800A
        EVENT_OBJECT_LOCATIONCHANGE = &H800B
        EVENT_OBJECT_NAMECHANGE = &H800C
        EVENT_OBJECT_DESCRIPTIONCHANGE = &H800D
        EVENT_OBJECT_VALUECHANGE = &H800E
        EVENT_OBJECT_PARENTCHANGE = &H800F
        EVENT_OBJECT_HELPCHANGE = &H8010
        EVENT_OBJECT_DEFACTIONCHANGE = &H8011
        EVENT_OBJECT_ACCELERATORCHANGE = &H8012
        EVENT_OBJECT_INVOKED = &H8013
        EVENT_OBJECT_TEXTSELECTIONCHANGED = &H8014
        EVENT_OBJECT_CONTENTSCROLLED = &H8015
        EVENT_SYSTEM_ARRANGMENTPREVIEW = &H8016
        EVENT_OBJECT_END = &H80FF
        EVENT_AIA_START = &HA000
        EVENT_AIA_END = &HAFFF
    End Enum

    ' SetWinEventHook Window Objects
    Friend Enum SWEH_ObjectId As Long
        OBJID_WINDOW = &H0
        OBJID_SYSMENU = &HFFFFFFFFUI
        OBJID_TITLEBAR = &HFFFFFFFEUI
        OBJID_MENU = &HFFFFFFFDUI
        OBJID_CLIENT = &HFFFFFFFCUI
        OBJID_VSCROLL = &HFFFFFFFBUI
        OBJID_HSCROLL = &HFFFFFFFAUI
        OBJID_SIZEGRIP = &HFFFFFFF9UI
        OBJID_CARET = &HFFFFFFF8UI
        OBJID_CURSOR = &HFFFFFFF7UI
        OBJID_ALERT = &HFFFFFFF6UI
        OBJID_SOUND = &HFFFFFFF5UI
        OBJID_QUERYCLASSNAMEIDX = &HFFFFFFF4UI
        OBJID_NATIVEOM = &HFFFFFFF0UI
    End Enum

    ' WinEventDelegate flags
    Friend Enum SWEH_dwFlags As UInteger
        WINEVENT_OUTOFCONTEXT = &H0     ' Events are ASYNC - No dll needed
        WINEVENT_SKIPOWNTHREAD = &H1    ' Don't call back for events on installer's thread
        WINEVENT_SKIPOWNPROCESS = &H2   ' Don't call back for events on installer's process
        WINEVENT_INCONTEXT = &H4        ' Events are SYNC, this causes your dll to be injected into every process
    End Enum

    ' SetWindowPos flags
    <Flags>
    Public Enum SWP_Flags As UInteger
        SWP_NOSIZE = &H1
        SWP_NOMOVE = &H2
        SWP_NOZORDER = &H4
        SWP_NOREDRAW = &H8
        SWP_NOACTIVATE = &H10
        SWP_DRAWFRAME = &H20
        SWP_FRAMECHANGED = &H20
        SWP_SHOWWINDOW = &H40
        SWP_HIDEWINDOW = &H80
        SWP_NOCOPYBITS = &H100
        SWP_NOOWNERZORDER = &H200
        SWP_NOREPOSITION = &H200
        SWP_NOSENDCHANGING = &H400
        SWP_NOCLIENTSIZE = &H800
        SWP_NOCLIENTMOVE = &H1000
        SWP_DEFERERASE = &H2000
        SWP_ASYNCWINDOWPOS = &H4000
    End Enum
End Class

多亏了Jimi的大力帮助，我才能让它正常工作：
将NativeMethods类添加到项目中，使用上面Jimi's answer中的代码
在表单中使用下列程式码：

Imports System.Runtime.InteropServices
Imports WindowsApp1.NativeMethods
Public Class Form1
    Private ReadOnly ForegrundChangedEventDelegate As WinEventDelegate
    Private Shared GCForegroundStateSafetyHandle As GCHandle
    Declare Auto Function SetParent Lib "user32.dll" (ByVal hWndChild As IntPtr, ByVal hWndNewParent As IntPtr) As Integer
    Declare Auto Function SendMessage Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer
    Declare Auto Function GetWindowThreadProcessId Lib "user32.dll" (ByVal hwnd As IntPtr, ByRef lpdwProcessId As Integer) As Integer
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim proc As Process
        Dim ProcId As Integer = 0
        proc = Process.Start("notepad.exe")
        proc.WaitForInputIdle()
        SetParent(proc.MainWindowHandle, Me.Panel1.Handle)
        SendMessage(proc.MainWindowHandle, 274, 61488, 0)
        GetWindowThreadProcessId(proc.MainWindowHandle, ProcId)
        SetForegroundStateChangedHook(proc.MainWindowHandle)
    End Sub
    Public Sub New()
        InitializeComponent()
        ForegrundChangedEventDelegate = New WinEventDelegate(AddressOf ForegroundStateChangedCallback)
        GCForegroundStateSafetyHandle = GCHandle.Alloc(ForegrundChangedEventDelegate)
    End Sub
    Protected Overrides Sub OnHandleDestroyed(e As EventArgs)
        GCForegroundStateSafetyHandle.Free()
        UnhookWinEvent(hForegrundChangedEventHook)
        MyBase.OnHandleDestroyed(e)
    End Sub
    Private Sub SetForegroundStateChangedHook(hWnd As IntPtr)
        Dim processId As UInteger
        Dim targetThreadId = GetWindowThread(hWnd, processId)
        hForegrundChangedEventHook = WinEventHookOne(SWEH_Events.EVENT_SYSTEM_FOREGROUND, ForegrundChangedEventDelegate, processId, targetThreadId)
    End Sub
    Friend Sub ForegroundStateChangedCallback(hWinEventHook As IntPtr, eventType As SWEH_Events, hWnd As IntPtr, idObject As SWEH_ObjectId, idChild As Long, dwEventThread As UInteger, dwmsEventTime As UInteger)
        If idObject = SWEH_ObjectId.OBJID_WINDOW AndAlso eventType = SWEH_Events.EVENT_SYSTEM_FOREGROUND Then
            Dim flags = SWP_Flags.SWP_ASYNCWINDOWPOS Or SWP_Flags.SWP_NOACTIVATE Or SWP_Flags.SWP_NOSIZE Or SWP_Flags.SWP_NOMOVE
            SetWindowPos(Handle, IntPtr.Zero, 0, 0, 0, 0, flags)
        End If
    End Sub
    End Class