Windows Phone: how to change the Application style programmatically - xaml

Question

In my Windows Phone 8 app, I have some implicit styles defined in a xaml file at the location /Styles/DefaultStyles.xaml
I have a similar file but with different colors, fonts, etc ... defined at /Styles/GreenStyles.xaml.
I reference the default style file in my App.xaml as follows :
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Styles/DefaultStyles.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
I want to make my app switch its implicit styles from the other styles file (GreenStyles) programmatically.
How can I achieve this ?
**
UPDATE:
I manged to change the source of the resource dictionary as follows:
ResourceDictionary style = App.Current.Resources.MergedDictionaries.ToList()[0];
string source = String.Format("/ApplicationName;component/Styles/GreenStyles.xaml");
style.Source = new Uri(source, UriKind.Relative);
Note: the word component must be written like that to avoid exceptions
Now I have an issue:
only the Implicit styles (the ones that do not have a x:Key attribute) are switched when the source of the dictionary changes.
any other style with a specified key and defined twice (with different attributes) in both files, will not be reflected in the UI.
so if I have these files:
DefaultStyles.xaml:
<Style x:Key="MainGrid" TargetType="Grid">
<Setter Property="Background" Value="Red"/>
</Style>
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="Red"/>
<Setter Property="FontSize" Value="24"/>
</Style>
</ResourceDictionary>
And:
GreenStyles.xaml:
<ResourceDictionary
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">
<Style x:Key="MainGrid" TargetType="Grid">
<Setter Property="Background" Value="Green"/>
</Style>
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="Green"/>
<Setter Property="FontSize" Value="24"/>
</Style>
</ResourceDictionary>
and I switched the source to point to GreenStyles.xaml, any Grid with the style MainGrid will still have it's background to Red.
What can be the reason for this ?

Answer 1

You can try using the approach Jeff Wilcox described here: http://www.jeff.wilcox.name/2012/01/phonethememanager/
Alternative approach is described here for Silverlight and I'm not sure if this will work on Windows Phone (though they share some codebase):
http://silverlightips.wordpress.com/2010/04/29/change-themestyle-using-merged-dictionaries/
Both of the ways are not easy if you have a large app and you may consider another option like (call me crazy)
<Button Style="{Binding Locator.Theme, Converter={StaticResource StyleThemeConverter}, ConverterParameter=RefreshButtonStyle}"
Hope this helps.