Proper way of hosting an external window inside WPF using HwndHost

Question

I'd like to host a window of an external process inside my WPF application. I'm deriving HwndHost like this:

    class HwndHostEx : HwndHost
    {
        [DllImport("user32.dll")]
        static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

        private IntPtr ChildHandle = IntPtr.Zero;

        public HwndHostEx(IntPtr handle)
        {
            this.ChildHandle = handle;
        }

        protected override System.Runtime.InteropServices.HandleRef BuildWindowCore(System.Runtime.InteropServices.HandleRef hwndParent)
        {
            HandleRef href = new HandleRef();

            if (ChildHandle != IntPtr.Zero)
            {
                SetParent(this.ChildHandle, hwndParent.Handle);
                href = new HandleRef(this, this.ChildHandle);
            }

            return href;
        }

        protected override void DestroyWindowCore(System.Runtime.InteropServices.HandleRef hwnd)
        {

        }
    }

and using it like this:

 HwndHostEx host = new HwndHostEx(handle);
 this.PART_Host.Child = host;

where handle is a handle for an external window I'd like to host and PART_Host is a border inside my WPF window:

<StackPanel UseLayoutRounding="True"
        SnapsToDevicePixels="True"
        Background="Transparent">
        <Border Name="PART_Host" />
...

This gives me an exception:

Hosted HWND must be a child window.

Sorry for my lack of knowledge but what is the proper way of hosting an external window inside WPF application?

Mcclean

Hi Mike, What is the handle object in HwndHostEx host = new HwndHostEx(handle); ? I am solving the same problem, and I am still could not find a solution. – Holey

@VivekDev: handle object in HwndHostEx is an IntPtr handle of an external window. You can get this here or here or here. Hope this helps. – Mcclean

Answer 1

Right before calling 'SetParent' do this:

public const int GWL_STYLE = (-16);
public const int WS_CHILD = 0x40000000;

SetWindowLong(this.ChildHandle, GWL_STYLE, WS_CHILD);

Cembalo

Note that this completely overrides the current window style. You might like to get the previous value, then set/mask values instead. – Rendezvous

Answer 2

Looking at the docs:

1. You need a Win32 control compiled for CLI
2. You must create the control inside your WPF app.

It seems not possibile to "attach" an already running Window from another process inside a WPF app.

How do you get the handle you pass to your HwndHostEx constructor?

Electro

Thanks for Your interest. Handle for this external window is returned by one of the methods in the DLL which produces it. What do You mean: "compiled for CLI"? – Mcclean

It means your "native code" must have metadata which allows to behave like (and interop with) "managed code". In practice if you have legacy Win32 C/C++ code you should upgrade it to a recent C++ version and compile it with the /clr complier switch. See msdn.microsoft.com/en-us/library/ms173265.aspx – Electro

I think that it is already done. The DLL is a C++ code which is wrapped to interop with C#. It shows a window and I'd just like to host it in my app. – Mcclean

Answer 3

To add clarification, here's the final code for hosting a process in a WPF app, taken from Jose's answer:

    class HwndHostEx : HwndHost
    {
        [DllImport("user32.dll")]
        static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

        [DllImport("user32.dll")]
        static extern int SetWindowLong(IntPtr hWnd, int nIndex, UInt32 dwNewLong);

        private IntPtr ChildHandle = IntPtr.Zero;

        public HwndHostEx(IntPtr handle)
        {
            this.ChildHandle = handle;
        }

        protected override System.Runtime.InteropServices.HandleRef BuildWindowCore(System.Runtime.InteropServices.HandleRef hwndParent)
        {
            HandleRef href = new HandleRef();

            if (ChildHandle != IntPtr.Zero)
            {
                const int GWL_STYLE = (-16);
                const int WS_CHILD = 0x40000000;

                SetWindowLong(this.ChildHandle, GWL_STYLE, WS_CHILD);


                SetParent(this.ChildHandle, hwndParent.Handle);
                href = new HandleRef(this, this.ChildHandle);
            }

            return href;
        }

        protected override void DestroyWindowCore(System.Runtime.InteropServices.HandleRef hwnd)
        {

        }
    }

// to create an instance:
var processName = "Whatever.exe";
var process = System.Diagnostics.Process.GetProcesses()
 .FirstOrDefault(item => item.ProcessName.ToLowerInvariant() == processName && item.MainWindowHandle != IntPtr.Zero);
var handle = process?.MainWindowHandle;

if(handle != null)
{
    var host = new HwndHostEx(handle.Value);

    YourControl.Grid.Children.Add(host);
}

Ladon

Thanks for putting the accepted answer in context. It helped a lot :) – Fanjet