Archive
VB gotcha: when If function isn’t equivalent to an If-Then-Else block
Just got bitten by the following:
Dim takeN As Integer = If(Integer.TryParse(EdTake.Text, takeN), takeN, itemsCount)
I had used that instead of writing in 2 lines:
Dim takeN As Integer
If not Integer.TryParse(EdTake.Text, takeN) then takeN = itemsCount
However, there’s an important difference:
“If” is a function, so its arguments are evaluated at call-time. The “If” signature is:
I guess the default is to pass arguments ByVal (by value) and not ByRef (by reference), although I’d expect the signature to specify it explicitly to avoid confusion. When one passes a literal value (say 15) to TruePart or FalsePart it just gets “boxed” into an Object, whereas if one passes an expression (e.g. “takeN+1” or even just “takeN”) it gets evaluated first, then result is boxed and passed as an Object.
So, whereas one might think (esp. if coming from the ALGOL “Call-By-Name” era) the 1st line to be equivalent to:
Dim takeN As Integer
If Integer.TryParse(EdTake.Text, takeN) then takeN = [RESULT OF TRYPARSE] else takeN = itemsCount
in fact it’s equivalent to:
Dim takeN As Integer
If Integer.TryParse(EdTake.Text, takeN) then takeN = [ANY] else takeN = itemsCount
where ANY is whatever the takeN variable one had defined contains.
I thought the VB compiler was warning when using a variable before having assigned a value to it, but it seems in this case it misses to issue a warning. In fact I just tried:
Public ReadOnly Property Take As Integer
Get
Dim takeN As Integer
Return takeN
End Get
End Property
and it still doesn’t complain. Strange, probably it sets new local variables to 0 by default, but it shouldn’t encourage a programming style that relies on implicit default values – such syntax usually means there’s a mistake in the source code that can lead to a nasty bug.
The moral of the story? Avoid such shorthand expressions and stick to classic keyword-based syntactical structures – after all structured programming had been introduced as an alternative to the many times incomprehensible programs written in functional programming languages (e.g. due to overuse of nested function calls).
Απαράδεκτες διαφημίσεις και από ΤΑ ΝΕΑ online
Κινούμενο πλαίσιο εμφανίζεται στο δεξιό μέρος της σελίδας που μας πληροφορεί ότι είμαστε ο 1.000.000 επισκέπτης. Τι λέτε ρε παιδιά, αλήθεια;
Ακολουθώντας το και δίνοντας τα στοιχεία σου (και ενώ σου τονίζει το “Χωρίς συνδρομή!”) τελικά καταλήγει να σου “προσφέρει” δυο άλλους “διαγωνισμούς” (συνεργατών τους λέει) που είναι οι κλασικοί που σε οδηγούν να γραφτείς σε ΥΠΠ (Υπηρεσίες Πολυμεσικής Πληροφόρησης), δηλαδή τα κλασικά SMS/MMS που σε χρεώνουν για τη λήψη τους.
Όταν στη συνέχεια σου έρθει και e-mail επιβεβαίωσης των στοιχείων που έδωσες για το (δωρεάν) διαγωνισμό (με χορηγούς δώρων GetItNow.gr κλπ. παρακαλώ!), ακολουθώντας το link βλέπεις άλλα δυο “ευχαριστήρια δώρα” που δεν είναι παρά ΥΠΠ και αυτά (και συνεχίζουν να σε παραπλανούν λέγοντας πως είσαι τάχα μου ο 999.999 επισκέπτης και σε αυτά). Έλεος!
Fix: Visual Studio 2010 XAML Designer output for WP7 light theme
The other day I submitted my 1st Windows Phone 7 application via http://create.msdn.com
Having registered for free as a student developer (being a PhD student on Robotics) via http://dreamspark.com I could only try my 1st app on WP7 emulator – when it gets accepted I will be able to have my WP7 phone unlocked to try apps there too.
So I was disappointed a bit to get back a certification failure. One of the two reasons stated was that I wasn’t following one key WP7 (design) guideline/requirement: to have the app UI work fine in both dark and light theme of WP7. I was using the default design colors and brushes, not having set any colors explicitly and since the emulator was starting in dark theme by default, this issue slipped my attention (wouldn’t it be nice if the Visual Studio XAML designer allowed you to switch between dark and light theme?).
The (nicely organized) feedback PDF from the Certification step of the WP7 app marketplace submission process was saying:
At first I couldn’t find the settings at the WP7 emulator since the image button pointing to the right to go to the settings page wasn’t visible (probably because of my video card not supporting the latest shader model and running the emulator ignoring the warnings shown that only Silverlight – not XNA – content will show up and probably not always fine – obviously meaning functionality that is implemented using GPU hardware acceleration in the emulator).
Dragging to the left on the 1st screen of the emulator (that just shows IE) takes you to the apps page where you also see Settings and your deployed app (apart from IE). You can hold down mouse on Settings there and select to Pin it to 1st page for easier access. At settings you can change the Theme Background to “light” instead of the default “dark” and try your app again.
In my app’s case indeed you couldn’t see a thing. The article that gave me a hint to what might be happening was:
http://timdams.wordpress.com/2011/06/21/creating-a-wp7-app-supporting-dark-and-light-themes/
and especially the phrase:
when the light theme is active, what WP7 basically does is switch the Foreground and the Background property of all controls, as long as they’re not defined explicitly.
The moment however, you define a specific color for a control, WP7 won’t help you with switching colors anymore
So I took a look again at the XAML code the Visual Studio 2010 designer for WP7 Silverlight app had generating. I noticed the XAML had Background=”Black” at various controls (like Grid, Pivot etc.).
Comparing with a newly created project I noticed it just had Background=”Transparent” for Grid. I later on remembered that at some point it was showing Pivot pages one over the other (due to wrong nesting in the XAML) which had set me changing the Background to “Black” at various controls trying to work around the overlap issue.
Doing a replace all for { Background=”Black”} (with a space prefix) and replacing with {} (that is nothing) is the first step needed for the fix.
The 2nd step is to add to the XAML header the missing Background="{StaticResource PhoneBackgroundBrush}" attribute value assignment shown below in bold that seems to be missing (to use the phone’s background brush by default).
In fact most probably the 2nd issue is with the Silverlight WP7 Pivot application template (probably the same goes for the Panorama template) and not the XAML designer itself which may be WP7 agnostic altogether.
<phone:PhoneApplicationPage
x:Class="MYPHONEAPPCLASSNAME.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
xmlns:controls="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768"
FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
Foreground="{StaticResource PhoneForegroundBrush}"
Background="{StaticResource PhoneBackgroundBrush}"
SupportedOrientations="PortraitOrLandscape"
Orientation="Portrait"
shell:SystemTray.IsVisible="True"
Title="MYPHONEAPPTITLE"
IsHitTestVisible="True">
A useful link regarding WP7 brushes is “Theme Resources for Windows Phone”:
http://msdn.microsoft.com/en-us/library/ff769552(v=vs.92).aspx
These suggestions have been submitted to Microsoft Connect and can be voted for at: https://connect.microsoft.com/VisualStudio/feedback/details/703467/vs2010-silverlight-xaml-designer-with-wp7-silverlight-app-templates-fail-at-wp7-light-theme
