ListView rendering changing when I render in CDDS_POSTPAINT

Question

So I've spent a whole load of time trying to render some text. I finally managed to get somewhere by subclassing the ListView and adding a WndProc override as follows:

protected override void WndProc(ref Message m) { base.WndProc( ref m );

            //NM_CUSTOMDRAW =-12
            switch( m.Msg )
            {
                case 0x004e://WM_NOTIFY:
                case 0x204e://WM_REFLECT_NOTIFY
                    {
                        NMHDR nmhdr     = (NMHDR)System.Runtime.InteropServices.Marshal.PtrToStructure( m.LParam, typeof( NMHDR ) );
                        if ( nmhdr.code == -12 )   //NM_CUSTOMDRAW
                        {
                            NMLVCUSTOMDRAW nmlvcd     = (NMLVCUSTOMDRAW)System.Runtime.InteropServices.Marshal.PtrToStructure( m.LParam, typeof( NMLVCUSTOMDRAW ) );
                            System.Diagnostics.Trace.WriteLine( nmlvcd.nmcd.dwDrawStage.ToString() );
                            if      ( nmlvcd.nmcd.dwDrawStage == 1 ) //CDDS_PREPAINT
                            {
                                int result  = (int)m.Result;
                                result      |= 0x10;//CDRF_NOTIFYPOSTPAINT;
                                m.Result    = (IntPtr)result;
                            }
                            else if ( nmlvcd.nmcd.dwDrawStage == 2 ) //CDDS_POSTPAINT
                            {
                                Graphics g  = Graphics.FromHdc( nmlvcd.nmcd.hdc );
                                if ( DrawFloatingItem != null )
                                { 
                                    PaintEventArgs pe   = new PaintEventArgs( g, nmlvcd.nmcd.rc );
                                    DrawFloatingItem( this, pe );
                                }
                            } 
                            else if ( nmlvcd.nmcd.dwDrawStage == 65537 )    //CDDS_ITEMPREPAINT 
                            {
                                int result  = (int)m.Result;
                                result      |= 0x10;//CDRF_NOTIFYPOSTPAINT;
                                m.Result    = (IntPtr)result;
                            }
                            else if ( nmlvcd.nmcd.dwDrawStage == 65538 )    //CDDS_ITEMPOSTPAINT 
                            {

                            }

                        }
                    }
                    break;
            }
        }

With this I've successfully managed to render over the list view. However the moment I do render (From the DrawFloatingItem event) then all the items shift up by the header's height (ie the first item is rendererd under the column header).

This is the list before:

And this is the list afterwards:

Has anyone got any idea what I am doing wrong here? If I comment out my draw commands (inside the "DrawFloatingItem" function) then everything works as expected. However the moment I do any drawing then the rendering goes wrong as above.

Any help would be massively appreciated!

In case your unaware you can often accomplish the same end without directly dipping into the underlying API: msdn.microsoft.com/en-us/library/… — Alex K.
@AlexK: OwnerDraw does not allow you to handle PostPaint. And yes .. I have already set OwnerDraw to true ... because if I didn't the NM_CUSTOMDRAW wouldn't be called in the first place. — Goz

Goz Goz · Accepted Answer · 2017-12-19T16:04:02

Its typical I always figure it out shortly after posting up a question. My mistake was that I wasn't disposing of the Graphics object I was creating before caling my DrawFloatingItem event.

Changing to the following fixed the problem:

 using( Graphics g  = Graphics.FromHdc( nmlvcd.nmcd.hdc ) )
 { 
     if ( DrawFloatingItem != null )
     { 
         PaintEventArgs pe   = new PaintEventArgs( g, nmlvcd.nmcd.rc );
         DrawFloatingItem( this, pe );
     }
 }

ListView rendering changing when I render in CDDS_POSTPAINT

1 Answers