Detecting resize width vs height

Question

My program lets users resize the form. I maintain the form ratio this way:

Private Sub frmMain_Resize(sender As Object, e As EventArgs) Handles Me.Resize
    dblRatio = Screen.PrimaryScreen.Bounds.Height / Screen.PrimaryScreen.Bounds.Width
    Me.Height = Me.Width * dblRatio
    ' me.width = me.height * dblRatio
End Sub

This works just fine if the user grabs the form from the side or the corners, but I can't do the same if resized from the top or bottom (or vice versa if I comment/uncomment me.height/me.width.)

If I knew how to detect what's being dragged, I could precede each with an "If" so only one or the other is executed.

Ideas? TIA

Answer 1

A way is to handle WM_SIZING

Something like this :

Protected Overrides Sub WndProc(ByRef m As Message)  
    If m.Msg = WM_SIZING Then  
        Dim nAspectRatio As Double = Screen.PrimaryScreen.Bounds.Width / Screen.PrimaryScreen.Bounds.Height  
        Dim windowRect, clientRect As RECT  
        GetWindowRect(m.HWnd, windowRect)  
        GetClientRect(m.HWnd, clientRect)  
        Dim nAddX As Integer = (windowRect.right - windowRect.left) - clientRect.right  
        Dim nAddY As Integer = (windowRect.bottom - windowRect.top) - clientRect.bottom  
        Dim rc As RECT = CType(Marshal.PtrToStructure(m.LParam, GetType(RECT)), RECT)  
        If (rc.bottom - rc.top + nAddY <= 200) Then  
            rc.bottom = rc.top + 200 - nAddY - 2  
        End If  
        Select Case CInt(m.WParam)  
            Case WMSZ_LEFT, WMSZ_BOTTOMLEFT, WMSZ_BOTTOMRIGHT, WMSZ_RIGHT  
                rc.bottom = CInt(rc.top + (CSng((rc.right - rc.left - nAddX)) / nAspectRatio) + nAddY)  
            Case WMSZ_TOPRIGHT, WMSZ_TOP, WMSZ_BOTTOM  
                rc.right = CInt(rc.left + (CSng((rc.bottom - rc.top - nAddY)) * nAspectRatio) + nAddX)  
            Case WMSZ_TOPLEFT  
                rc.left = CInt(rc.right - (CSng((rc.bottom - rc.top)) * nAspectRatio) + nAddX)  
        End Select  
        Marshal.StructureToPtr(rc, m.LParam, False)  
        m.Result = CType(1, IntPtr)  
        Return  
    End If  
    MyBase.WndProc(m)  
End Sub  

with declarations :

<StructLayout(LayoutKind.Sequential)>  
Public Structure RECT  
    Dim left As Integer  
    Dim top As Integer  
    Dim right As Integer  
    Dim bottom As Integer  
End Structure  
  
<DllImport("User32.dll", SetLastError:=True)>  
Public Shared Function GetClientRect(hWnd As IntPtr, ByRef lpRect As RECT) As Boolean  
End Function  
  
<DllImport("User32.dll", SetLastError:=True)>  
Public Shared Function GetWindowRect(hWnd As IntPtr, ByRef lpRect As RECT) As Boolean  
End Function  
  
Public Const WMSZ_LEFT = 1  
Public Const WMSZ_RIGHT = 2  
Public Const WMSZ_TOP = 3  
Public Const WMSZ_TOPLEFT = 4  
Public Const WMSZ_TOPRIGHT = 5  
Public Const WMSZ_BOTTOM = 6  
Public Const WMSZ_BOTTOMLEFT = 7  
Public Const WMSZ_BOTTOMRIGHT = 8  
  
Public Const WM_SIZING = &H214