Introduction
Often if you work with inheritance with System.Windows.Forms or
use third party stuff (preferred where you do not have the source) and hit
Shift+F7 (View Designer), a blank white page is the only thing the designer is
able to show. Normally you're confused, don't know where to start searching for
this unexpected feature of VS.NET Designer. Maybe it could be the last lines of
code you added today, or it could be code that nobody remembers, 'cause it was
written last month from a external worker. What to do know? You should check in
your code running in a few hours ?
Background
It's my job to write the UI front end library for the company i work today.
There are 5 team members, which have to use my code. Every time the designer
shows a white blank page, my name is called and i have to (try) fix it as fast
as possible, not nice if you don't where to search the bug.
Solution Configuration
Visual Studio supports different Solution Configurations (sc), debug and
release are the default ones. 'Cause we're able to add/delete this sc, we're
able to add a new sc which supports design time debugging. If you're able to
debug the design time, you're able to find the exception that killed the
designer, you remember, blank white page.
- Right click your solution and choose the Configuration Manager...
context menu item.
- In the "Configuration Manager" choose <New>.
- Specify a name for your new solution configuration.
- Hit Ok twice, the created sc is now selected.
- Right click your project and choose "Properties" context menu item
- The well known project property pages are now open, select Configuration
Properties\Debugging
- Switch Debug Mode to Program.
- Let Start Application point to your devenv.exe file. See also
screenshots are available here (animated gif which opens in new window).
Exceptions
Now hit Ctrl + Alt + E, or choose Exceptions under main menu
Debug\Exceptions. Because we don't know exactly which exception type
we're trying to find, we best choose Break into debugger for the
Common Language Runtime Exceptions. After playing around with the white
blank page problem I know that System.BadImageFormatException is
thrown.
Bust it
The good news is that you're now ready to bust those tricky exceptions which
kicks our designer. The bad news is that the designer does not work proper cause
there are exceptions in our code. We did something, that is not valid in design
time, but will executed there. Or there is another exception of certain kind,
also not valid for design time.
- Hit F5 to start debugging, as you expected Visual Studio starts another
Visual Studio instance where you will
- Open the same solution you just prepared for design time debugging.
- View the form in design mode that normally cause the designer to fall.
- Behind your current Visual Studio should appear the well known exception
dialog, hit Break and you see the code thrown it.
- Repeat this steps until you're code is exception free (illusion), but sure
till the designer work proper.
The demo application gives you a good sample, if you try to load form2 in
designer, he crashes. Please make sure that the path to the devenv.exe
reflects your current installation, otherwise the debug mode will not work
proper.
Conclusions
- I hope with this knowledge you could solve your design time problems, for my
own it does.
History
Have fun with it...
