c# - Proper way of hosting an external window inside WPF using HwndHost -

i'd host window of external process inside wpf application. i'm deriving hwndhost 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 this:

 hwndhostex host = new hwndhostex(handle);  this.part_host.child = host; 

where handle handle external window i'd host , part_host border inside wpf window:

<stackpanel uselayoutrounding="true"         snapstodevicepixels="true"         background="transparent">         <border name="part_host" /> ... 

this gives me exception:

hosted hwnd must child window. 

sorry lack of knowledge proper way of hosting external window inside wpf application?

right before calling 'setparent' this:

public const int gwl_style = (-16); public const int ws_child = 0x40000000;  setwindowlong(this.childhandle, gwl_style, ws_child);