Designer: mysterious behavior with form constructers and static methods

[Sebastian Bargmann]

Hi,

[C# / VS2003]

I've run into a weird problem with the form designer. I have three classes:
a messagebox class and two forms (Base and Derived which is derived from
Base):

(note: only relevant code below)

<code>

public class MyMsg
{
[DllImport("user 32.dll", EntryPoint="Mes sageBoxW",
CharSet=CharSet .Unicode, ExactSpelling=t rue,
CallingConventi on=CallingConve ntion.StdCall)]
private static extern IntPtr MessageBox(UInt 32 hWnd, string AText,
string ACaption, UInt32 AType);

public static void Show(string AText)
{
MessageBox(0, AText, "Caption", 0);
}
}

public class BaseForm : System.Windows. Forms.Form
{
public BaseForm()
{
InitializeCompo nent();

MyMsg.Show("Tes t");
}
}

public class DerivedForm : BaseForm
{
public DerivedForm()
{
InitializeCompo nent();
}
}

</code>

When I show DerivedForm in the designer my messagebox is shown. When I show
BaseForm in the designer, the messagebox is NOT shown. What gives?! Is this
a bug?

Are there any specifications of what and what isn't created/shown/whatever
designtime vs. runtime?

I know the above code doesn't really make sense, but its a simplification of
some similar code used for singleton patterns...


Regards,
Sebastian

[Frank Hileman]

Re: Designer: mysterious behavior with form constructers and static methods

Hello Sebastian,

When you edit a form or any other root component in the designer, the class
of the form is not instantiated. Instead, its base class is instantiated.
Something is needed to serve as the root component, but to obtain the latest
code from the InitailizeCompo nents method, which may not be compiled (the
form may not even be compilable), instead of instantiating the class you are
working on, the base class is instantiated, and the IntializeCompon ents
method is interpreted using a CodeDom interpreter built into VS. So only the
code in there will be interpreted, and of course the interpreter is somewhat
limited. This is why the message box appears when working on the derived
class: the base class code is actually run and not interpreted.

Regards,
Frank Hileman
Prodige Software Corporation

check out VG.net: www.prodigesoftware.com/screen5.png
An animated vector graphics system integrated in VS.net
beta requests: vgdotnetbeta at prodigesoftware .com

"Sebastian Bargmann" <sb@removedbeca useofspam.dk> wrote in message
news:fqqvb.2735 $My5.1301@news. get2net.dk...[color=blue]
> Hi,
>
> [C# / VS2003]
>
> I've run into a weird problem with the form designer. I have three[/color]
classes:[color=blue]
> a messagebox class and two forms (Base and Derived which is derived from
> Base):
>
> (note: only relevant code below)
>
> <code>
>
> public class MyMsg
> {
> [DllImport("user 32.dll", EntryPoint="Mes sageBoxW",
> CharSet=CharSet .Unicode, ExactSpelling=t rue,
> CallingConventi on=CallingConve ntion.StdCall)]
> private static extern IntPtr MessageBox(UInt 32 hWnd, string AText,
> string ACaption, UInt32 AType);
>
> public static void Show(string AText)
> {
> MessageBox(0, AText, "Caption", 0);
> }
> }
>
> public class BaseForm : System.Windows. Forms.Form
> {
> public BaseForm()
> {
> InitializeCompo nent();
>
> MyMsg.Show("Tes t");
> }
> }
>
> public class DerivedForm : BaseForm
> {
> public DerivedForm()
> {
> InitializeCompo nent();
> }
> }
>
> </code>
>
> When I show DerivedForm in the designer my messagebox is shown. When I[/color]
show[color=blue]
> BaseForm in the designer, the messagebox is NOT shown. What gives?! Is[/color]
this[color=blue]
> a bug?
>
> Are there any specifications of what and what isn't created/shown/whatever
> designtime vs. runtime?
>
> I know the above code doesn't really make sense, but its a simplification[/color]
of[color=blue]
> some similar code used for singleton patterns...
>
>
> Regards,
> Sebastian
>
>
>[/color]

[Sebastian Bargmann]

Re: Designer: mysterious behavior with form constructers and static methods

Hi Frank - thanks for your answer,

So this behaviour is actually by design. I see...

One way to prevent the dialog (MyMsg.Show()) to be shown in the designer, is
to move it to the base-form's OnLoad method and then check the DesignMode
property (since DesignMode isn't valid in the ctor).

Are there other alternatives?


Regards,
Sebastian Bargmann


"Frank Hileman" <frankhil@no.sp amming.prodiges oftware.com> wrote in message
news:%23JmXS1Js DHA.1760@TK2MSF TNGP10.phx.gbl. ..[color=blue]
> Hello Sebastian,
>
> When you edit a form or any other root component in the designer, the[/color]
class[color=blue]
> of the form is not instantiated. Instead, its base class is instantiated.
> Something is needed to serve as the root component, but to obtain the[/color]
latest[color=blue]
> code from the InitailizeCompo nents method, which may not be compiled (the
> form may not even be compilable), instead of instantiating the class you[/color]
are[color=blue]
> working on, the base class is instantiated, and the IntializeCompon ents
> method is interpreted using a CodeDom interpreter built into VS. So only[/color]
the[color=blue]
> code in there will be interpreted, and of course the interpreter is[/color]
somewhat[color=blue]
> limited. This is why the message box appears when working on the derived
> class: the base class code is actually run and not interpreted.[/color]

[Frank Hileman]

Re: Designer: mysterious behavior with form constructers and static methods

Sebastian, without knowing more about your specific code I don't think I can
give an intelligent answer. - Frank

"Sebastian Bargmann" <sb@removedbeca useofspam.dk> wrote in message
news:jhjwb.2207 $DO6.414@news.g et2net.dk...[color=blue]
> Hi Frank - thanks for your answer,
>
> So this behaviour is actually by design. I see...
>
> One way to prevent the dialog (MyMsg.Show()) to be shown in the designer,[/color]
is[color=blue]
> to move it to the base-form's OnLoad method and then check the DesignMode
> property (since DesignMode isn't valid in the ctor).
>
> Are there other alternatives?
>
>
> Regards,
> Sebastian Bargmann[/color]

[Sebastian Bargmann]

Re: Designer: mysterious behavior with form constructers and static methods

Hi Frank,

There really isn't any more to it than you have already seen. My real
problem is probably that I need to (well, I'd like to) know how code
behaves when run in the designer vs. "normal" run.

E.g. Are there any methods or properties on UserControl (or its parents)
that behaves differently when running in the designer (DesignMode is on such
property).

I have worked a lot with Delphi and VC++ and I'm used to be able to check
the source of VCL/MFC if there's something I don't understand. Apparanty I'm
not so lucky with dotNET...

Best regards,
Sebastian


"Frank Hileman" <frankhil@no.sp amming.prodiges oftware.com> wrote in message
news:eubLowosDH A.3436@tk2msftn gp13.phx.gbl...[color=blue]
> Sebastian, without knowing more about your specific code I don't think I[/color]
can[color=blue]
> give an intelligent answer. - Frank[/color]