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Archive for May, 2010

WPFGlue goes WPF 4.0

May 23, 2010 Leave a comment

When VS 2010 was released, I was quite eager to shift to the new version of the framework: the last two releases had brought a lot of real improvements, so I expected the new release to do likewise. Therefore, I upgraded the WPFGlue code to .Net 4.0 and tried it out. These were my experiences:

Upgrade Experience

Upgrading went real smooth: it’s possible to install VS 2010 parallel to VS 2008, so I did that, copied my projects to the new version’s project folder, and opened them. After completing an Upgrade Wizard, there I was… No problem at all, and the Upgrade Wizard didn’t have to change any code, it just set the projects to target the .Net 4.0 Framework instead of .Net 3.5 . (Cool feature: in VS 2010 Express you can select the targeted framework version in the compile options, and you can select older and (hopefully) even newer versions than the one that comes with the VS installation). I have been running VS 2010 and VS 2008 in parallel ever since, and so far haven’t experinced any problems with that.

However, when testing the examples again, there were a few glitches:

  • The LocalizedList in the WPFGlue.Localization namespace caused an error message in the XAML designer.
  • There was a problem with Bindings when navigating backwards through the navigation history in a NavigationWindow.

Error Message in the XAML Designer

The new XAML designer is supposed to be more robust and to be more consistent with the Blend XAML designer. However, one of the tricks I did with the LocalizedList class caused it to hiccup: On this class, I implemented IList so one could set the child elements directly. This was due to the fact that the VS 2008 XAML designer was not handling this very graceful, and I wrote the class before I found out what one has to do to have proper support for typed collections. At the same time, this class can be used as a converter in bindings, in order to translate Enum values into human readable localized strings.

The combination of IList and IValueConverter seemed to be too much for the designer: while the application was compiling and running alright, the designer kept showing squiggly lines about an unset object reference in the XAML pane.

Debugging custom mark-up extensions in VS 2010 Express Edition is a little bit painful. I would recommend to buy the full version if you consider this, and meanwhile I’d recommend to keep away from them… Anyway, I found out that the error message goes away if you don’t implement IList on the same class as IValueConverter, so I just followed the pattern described in the Coding for XAML post.

I posted this problem on the Connect website as product feedback, but they decided to not do anything about it, which I can understand.

TextBox Bindings not Restored when Navigating Backwards

I found this problem first in this thread in the MSDN WPF forum. When you have a page that has data-bound TextBoxes, navigate away from the page and then go back using the Back button of the NavigationWindow that contains the page, the TextBoxes come up blank, even though the DataContext of the page and TextBox is set correctly. It seems that the XAML of the Page is not read the same way when the page is re-displayed; I tried to solve the problem with a custom mark-up extension, and the extension was not instantiated when the page was revisited. So, I tried a DataTemplate instead, and that worked. Finally, I came up with wrapping the page contents into a UserControl. The UserControl seems to read its XAML definition every time it is displayed, and since it inherits the correct DataContext, the problem goes away.

Still, I think this is quite a serious glitch. I posted it to Connect as well, the answer is pending.

Conclusion

Having these strange kinds of errors was a little bit sobering about .Net 4.0. Even so, since I found workarounds, and since the new framework has some cool new features I hope to be using soon, I’m going to stick to it.

So, I updated the downloads page with projects targeting the new version. I’m still keeping copies of the WPF 3.5 version, as well, but I’m not going to include new code into these versions.

Coming Soon…

The next thing I’m planning to do is to research the object lifetime events in WPF 4.0. I was stopped in my tracks a little bit when I found out that the pattern of Loaded and Unloaded events is not quite what one expects (this was still under WPF 3.5), and I’d like to find out what happens there exactly.

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