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Resize Calendar in WPF application

I found a lot of similar questions on internet but no solutions to solve my problem.
The problem is really simple, I just want to resize a calendar, nothing more. Many people recommanded to use a Viewbox like that :
<Viewbox
Width="400"
Height="400"
Stretch="Fill"
StretchDirection="Both">
<Calendar />
</Viewbox>
This solution seems to work for many guys that faced the same issue, but didn't work for me as you can see on the snapshot below :
result of above code
I have tried other values for StrechDirection but nothing is getting better.
The ViewBox is inside a simple UserControl.
Thanks in advance

I found the problem. I have changed my buttons style for the whole application. Because a calendar contains a lot of buttons, each button in the calendar were impacted by my buttons style.

Listbox with thousand of images in a wrappanel

I'm trying to create a listbox that may contain over a thousand images in a grid like design. In term of design it would be quite similar to this:
Since I can't use a wrappanel as that would break UI virtualization and a stackpanel can't list images in such a grid(?), I'm trying to solve this issue using a modified version of https://virtualwrappanel.codeplex.com
My XAML:
<ListBox x:Name="GameWheel" ItemsSource="{Binding GameData}" ScrollViewer.HorizontalScrollBarVisibility="Hidden" ScrollViewer.VerticalScrollBarVisibility="Hidden">
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<c:VirtualizingWrapPanel IsItemsHost="True" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate>
<Image x:Name="GameImage" Source="{Binding Path=ImagePath}" Width="{Binding ElementName=GameWheel, Path=ActualWidth, Converter={StaticResource widthConverter}}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
While this approach works, it's still quite slow and buggy, especially when using bind on the image width. Is there a better way of archiving the same result? Without the custom wrappanel preferably.

Check out my implementation of VirtualizingWrapPanel. Also available (with more included) from NuGet.
This code originally came from this CodeProject article which mostly worked and appears to be the same place you started. Along the way I fixed several bugs and improved performance so it might help you as well.
Update: The key is going to be to bind to the VirtualizingWrapPanel.ItemWidth rather than Image.Width. There was a bug in both implementations of the VirtualizingWrapPanel that would prevent the children from being resized if the ItemHeight or ItemWidth values changed. I fixed this bug in this commit (line 358).
Admittedly it's a brute force fix but I wanted to get something checked in for you and have to head out. I tested it with 10,000 images and it was very snappy. I'll work on a better solution (ie: only remeasure when we know the value has changed) and update this answer when I do.
Update 2: Quick change to improve the child.Measure with this commit.
//TODO: If either child Height or Width == PositiveInfinity and the other side == ChildSlotSize then we probably don't need to measure. Need to test this
if (!child.DesiredSize.Equals(ChildSlotSize))
{
child.Measure(ChildSlotSize);
}
Still room for improvement but no time for proper testing right now and this works.

Windows Phone 8 Font Binding

I'm really stumped on how to go about binding fonts to a textbox. I'd like for my user to be able to choose between 3-4 different fonts. I have something like this right now:
<TextBox x:Name="MyTextBox" AcceptsReturn="True" FontSize="20"
FontFamily="{Binding FontSelection}" />
But I have no clue how the c# should look, and I had no luck googling for it. What is the best way to do this? Do I have to create an observable collection? I've tried adding fonts to the Application.Resources, but it wouldn't let me.
Thanks for any answers!

This FontSelection property has to be single item. You could first try simple valid string (like 'Arial'), it could work. Another approach is FontFamily type as poined out by Romasz.
Also there are Converters available, quite easy to implement. http://channel9.msdn.com/Series/Windows-Phone-8-1-Development-for-Absolute-Beginners/Part-25-Advanced-Binding-with-Value-Converters With this you could save user font selection as simple number for example and convert it to appropriate type with Converter.

Terrible performance of MapControl with multiple children in Windows Phone 8.1 Runtime

I have a MapControl which is supposed to be filled with multiple objects (500+). These objects represent some kind of POI. When the user taps on the object (pushpin) I display more info about the POI. So, I need:
A MapControl capable of handling high amount of child objects
Intercept Tappedevent of the child object
In order to achieve the second goal I decided to define my own pushpin template:
<maps:MapControl x:Name="Map">
<maps:MapItemsControl ItemsSource="{Binding Pushpins}">
<maps:MapItemsControl.ItemTemplate>
<DataTemplate>
<Image Width="40"
Height="40"
Source="{ ... }"
Tapped="OnPushpinTappedAsync"
maps:MapControl.Location="{Binding Location}"
maps:MapControl.NormalizedAnchorPoint="{Binding AnchorPoint}" />
</DataTemplate>
</maps:MapItemsControl.ItemTemplate>
</maps:MapItemsControl>
</maps:MapControl>
This works great except for the fact that.. the visual out of such approach is AWFULL. Every time I move a map, every Pushpin flickers a lot. It's like they are not, I don't know, bound to the position. They are also lagging. It looks really bad. Rendering of those objects is really poor.
The alternative is to add elements to the MapControl's MapElements property. It makes rendering of those objects really nice.
But then I loose binding ability and will have to workaround it - I'm not a big fan of that. There's also a second problem - from what I've read, rendering objects of the MapElements collection is a best effort deal. So it does not guarantee that it will succeed. And that is not an option for me, as in the future I plan to add clustering functionality, so I need to have a full control over what is being rendered on the map and what is not.
Do you have any idea why these MapControl's elements flickers so much? What can I do to prevent it? Thanks in advance for any hint or answer.

I'm facing the exact same problem. Seems to me, that the MapControl is completely broken. There are many more bugs besides performance :(
You cannot really solve the problem, but you can create a "oldschool" WP8.0 Silverlight application and use something like this:
<Page xmlns:map="clr-namespace:Microsoft.Phone.Maps.Controls;assembly=Microsoft.Phone.Maps">
<map:Map Grid.Row="1" x:Name="myMap">
<tool:MapExtensions.Children>
<tool:MapItemsControl>
... and so on ...
This performs great but of course you have to change everything from Win(P)RT to Silverlight...

I too faced this problem, but I find this library to be usefull.
Hopefully Microsoft updates the MapControl for Windows 10.

Try this:
Tag="{Binding index_of_collection}"
and this:
OnPushpinTappedAsync()
int index = (int)(sender as Image).Tag; //index_of_collection

Windows 8 Data Binding

I'm developing an application using C# and XAML and I've encountered a problem that is confusing me. I have a property in my data called GroupImage and have used binding to set the Source property of an Image with it. That worked fine but when I wanted to do the same thing a second time it doesn't show the image in the second Image control.
<Image Source="{Binding Group.GroupImage}" Width="250" Height="500" Stretch="UniformToFill" />
<Image VerticalAlignment="Bottom" Stretch="UniformToFill" Source="{Binding Group.GroupImage}" Grid.RowSpan="2"/>
The top one works fine the bottom one doesn't. I have been reading about Data Binding and have gotten the impression that you need to specify something in the DataContext to use a property more than once. Is this right? It seems a very strange way of doing this.
I am relatively new to C# so sorry if I'm missing something obvious. I'd appreciate a more knowledgeable cluing me in.
Thanks
Update Following the assistance I received I figured out that the context was being set to
DataContext="{Binding Group}"
And as a result my second line needed to change to the following since the Data Context was already set to Group.
<Image VerticalAlignment="Bottom" Stretch="UniformToFill" Source="{Binding GroupImage}" Grid.RowSpan="2"/>

You don't need to specify something in the DataContext to use a property more than once. But your two Image have to have the right DataContext (you can easily test it with the debugger), depending on their location on the visual tree (You didn't provide any code for the DataContext part ?) .
You can also check that your Image's Width/Height are not 0.