Corrado's Blog 2.0

Online thoughts of a technology funatic

Beware of generated XAML in UWP

I admit, this is s strange blog post title but that’s what this post is going to talk about.

I’m working on a UWP app that has different min and target runtimes:


After doing some UI work with Visual Studio & Blend I’ve discovered that the app was crashing on machines without Anniversary edition installed. At the end of a debuggin session I’ve found the reason: The XAML template generated by the tools contains incompatible elements (resources mainly, but also new properties) that are not present on previous builds.

To give you an example, this is an extract from a ComboBox default template, generated by Blend when you use the Template->Edit copy feature:


<Setter Property="Foreground"

Value="{ThemeResource SystemControlForegroundBaseHighBrush}" />

14393 (Anniversary)

<Setter Property="Foreground"

Value="{ThemeResource ComboBoxForeground}" />

The reason of this is because the tools generate the template from the Target version SDK and not the Min version SDK that might even not be present.

The team said that they’re going to give you some warnings in the future when situations like this happen, but in the meantime, at least when you’re doing design work, be sure to selected, the min target version SDK otherwise you might end up in troubles.

The tale of a GridViewItem customization

Once upon a time, in a galaxy not so far away, there was a guy (me Smile) who was working on a Windows Store 8.1 application and was asked to create a GridView whose items should look like this picture:


The guy (again, me) thought: What’s the problem, did it many times! and he started setting a data source:

public class Item
        public string Text { get; set; }

    public class DemoViewModel
        public DemoViewModel()
            this.Items = new List<Item>();
            for (int i = 0; i < 10; i++)
                this.Items.Add(new Item() { Text = "Item " + i });

        public IList<Item> Items { get; set; }

He then added a GridView to a page, bound the data source and created a simple ItemTemplate:

<Page x:Class="GridViewDemo.MainPage"
        <local:DemoViewModel x:Key="vm"></local:DemoViewModel>
        <DataTemplate x:Key="MyItemTemplate">
            <Grid Width="100"
                <TextBlock HorizontalAlignment="Center"
                           Text="{Binding Text}"
                           VerticalAlignment="Center" />

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
          DataContext="{StaticResource vm}">
        <GridView ItemsSource="{Binding Items}"
                  ItemTemplate="{StaticResource MyItemTemplate}"

Run the solution and he got something quite close to what he was asked to realize:


Ok, just a couple of customizations and we’re done, he thought…

Let’s start with the selected background: The guy knows that background brush is managed inside ItemContainerStyle so he fired up Blend 2013, edited GridView’s ItemContainerStyle and here’s what he got:


Just a simple GridViewItemPresenter that has a series of Brush properties that give you the opportunity to customize several container aspects


In his case he needed to customize the color of SelectedBackground so, since it is bound to a resource named ListViewItemSelectedBackgroundThemeBrush he added a Brush resource with the same name inside Page resources and selected state was done, here’s updated result:

<SolidColorBrush x:Key="ListViewItemSelectedBackgroundThemeBrush"


But a question started to rise in his mind: “How to i set default (gray) background color?” there’s no Background color exposed by GridViewItemPresenter nor he can set it inside ItemTemplate otherwise it wouldn’t change when item is selected.

He tried lookind inside MSDN docs hoping to find a brush key that controls item default background but he had no luck Sad smile and navigated a lot the Internet until he realized he did something similar in the past for a Windows 8.0 application.

He then opened that old source code and discovered what has changed: The GridViewItemPresenter has been introduced in Windows 8.1, here’s how ItemContainerStyle looks in Windows 8.0:


Since you have access to all the elements composing the GridViewItem what the guy did was copying the style into Windows 8.1 app and edited VisualStateManager states (I’m sure, dear reader, you know how to do that…)

So, here’s final result:


The guy secretly told me that he wasn’t happy for such solution, probably GridViewItemPresenter has been introduced to improve GridView’s performances but he found no other easier way to solve the puzzle.

Based on a true story… Smile

PS: In case you need Windows 8.0 GridView’s ItemContainerStyle you can get it here.

Debug design time issues in Blend 2013

In 2010 (wow! that’s a long time ago…) I blogged about how to debug Blend design time exceptions, since then things have changed, Blend and Visual studio designer merged and so the XAML designer is now hosted in a separate process named XDesProc.exe (at least in Windows Store applications)

Laurent Bugnion has a detailed blog post about how to attach Visual Studio debugger to Blend to debug a Windows Store application at design time so i won’t repeat it here, the reason of this post is to integrate it with another step required when you use Visual Studio 2013 and Blend 2013.

Since with latest release PDB are no longer copied to cache location used by designer your simbols won’t be loaded and your attach procedure won’t work.

The solution is very easy, just point the debugger symbols to the proper PDB files of your application and everything will work as expected.

To point the PDBs just use: Tools –> Options-> Debugger


Then add the folder where your app’s PDB file resides.

Blend can’t locate types in external assemblies

While developing a Windows Store app I run into a Blend issue that caused me some headache.

I tend to define common converters in external assemblies in order to reuse them in other projects, so i added a reference to a Windows Store library project containing the converters I needed then swiched to Blend to use them from Create DataBinding dialog, and here’s what i got:


Problem: My library was not listed.

Really weird since here’s what I got doing the same from Visual Studio 2012


My MvvmHelper library is listed. Confused smile

Using Visual Studio to add the assembly resulted in following Blend error:


Ok, i presume you probably want to know the reason (and how to fix it): The problem was caused by projects having different build configurations: that main project has a X86 configuration (required by Bing Maps component) while all referenced libraries where AnyCPU and looks like that Blend 2012 doesn’t like it.

Moving the entire solution to X86 solved the issue.

Blend team is working on having it fixed before Blend 2013 release.

Happy Blending!

Note: Many thanks to @unni for helping me on this.