Determine Form Size from another Form

Question

VB2012: In order to do some calculations in my main form I need to know the form size of a secondary form. The form size may change from user to user depending on OS and theme. I understand that the client size stays the same. However I think I am not doing something correctly as I get different numbers depending on where I call for the form size.

As an illustration here is my main form where on the load event I attempt to get the size of an Alert form

Private Sub frmMain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    'get the default width and height of an Alert form.
    Dim frmW As Integer = frmAlert.Width 'in pixels
    Dim frmH As Integer = frmAlert.Height 'in pixels
    Dim frCsW As Integer = frmAlert.ClientSize.Width 'in pixels
    Dim frmCsH As Integer = frmAlert.ClientSize.Height 'in pixels
    Debug.Print("frmW={0} frmH={1} frCsW={2} frmCsH={3}", frmW, frmH, frCsW, frmCsH)
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    'set up a new alert form
    Dim frm As New frmAlert

    'show the alert form
    frm.StartPosition = FormStartPosition.CenterParent
    frm.Show()          'with this option the Alert Forms stay on the screen even if the Main form is minimized.
End Sub

Now the Alert form is set with FormBorderStyle=FixedDialog, ControlBox=False, MaximizeBox=False, and MinimizeBox=False and in the Alert form I have this on the load event:

Private Sub frmAlert_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Debug.Print("me.width={0} me.height={1} cs.width={2} cs.height={3}", Me.Width, Me.Height, Me.ClientSize.Width, Me.ClientSize.Height)
End Sub

and here is the debug output

frmW=380 frmH=168 frCsW=374 frmCsH=162
me.width=390 me.height=200 cs.width=374 cs.height=162

As expected the client size is the same but the total form size is different. I am trying to wrap my head around the differences in .Height and .Width. No other code exists to change the form properties. The second debug statement matches the form Size in the IDE designer. Why are the dimensions different? How would I properly query to get the form size from another form?

Answer 1

Before the form is shown it will have a smaller size compared to when it is visible. This is because when you show the form Windows will do all kinds of stuff to it based on the user's screen and theme settings, such as:

• Resize it if the user has different DPI settings.
• Apply borders to it based on the user's selected window theme.
• (etc.)

Your best bet is to show the form first, then get its size.

If you don't want the form to be visible right away you can set its Opacity property to 0 to make it invisible, then change it back to 1.0 once you need the form to be shown to the user.