Resource behavior inconsistency for ItemTemplates of list controls in Anniversary Update

It appears that the Anniversary Update has a hidden buggy behavior concerning Resources in ItemTemplates of list controls. I have hit this problem while working on an UWP app and I will describe the problem along with a workaround, which you can use to make sure your app will behave correctly on all versions of Windows 10. Continue reading “Resource behavior inconsistency for ItemTemplates of list controls in Anniversary Update”

When a single transparent color is simply not enough

There are countless times in the life of a Universal Windows Platform app developer when the “Transparent” color comes handy. However, it is good to remember that “Transparent” is still just a color, otherwise you can encounter some unwelcome surprises.

Animation of "Transparent" color
On the left is the animation from “Transparent” to White, on the right from “Transparent” to Black

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Using custom nuget.exe in VSTS build process

Soon after the release of Visual Studio 2017, the Visual Studio Team Services team has added a Hosted VS2017 build agent that has support for all the latest and greatest technologies. Unfortunately although the build task with Visual Studio 2017 is itself present, the newest version of NuGet wasn’t added, yet. Fortunately, it is possible to use a custom nuget.exe to circumvent this issue and be able to restore packages for project using the new csproj format with <PackageReference>. Continue reading “Using custom nuget.exe in VSTS build process”

Modifying UWP navigation backstack with MvvmCross

While developing mobile apps, you may encounter the need to clear or pop the navigation stack to remove specific pages from appearing when the user navigates back. Because MvvmCross framework has a lot of abstractions above the target operating systems, it does not contain a built-in mechanism to manipulate the back stack. How can we use the framework capabilities to implement this requirement in a clean fashion?

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Forcing the CommandBar to open down

The CommandBar  control is a vital component of UWP app design. It is an evolution of the AppBar  concept, which was available ever since Windows Phone 7, but with UWP is much more feature complete. One thing that is still missing however is the option to choose the direction in which the command bar opens.

Problem

The default behavior of the CommandBar  is to open in the up direction whenever the control is not at the very top of the window. This is an issue, because this holds true even when we define a custom title bar on Desktop, in which case the CommandBar  opens below the window’s minimize, maximize and close buttons which doesn’t look good at all.

The default template

The default template of the CommandBar  control defines the states of the control as a collection of VisualStates  and VisualStateTransitions . It turns out that there is always a separate visual state for down and up direction.

Inside these states you can see that the system just uses different values for some of the properties like CommandBarTemplateSettings.ContentHeight  vs CommandBarTemplateSettings.NegativeOverflowContentHeight  for the Y  property of OverflowContentRootTransform .

Solution

We cannot easily change the inner logic of the control itself, but we can make the control in up-open state look identical as it does for down-open state. This can be achieved purely by copy-pasting the Storyboards  from ...OpenDown visual states and visual state transitions to the respective ...OpenUp  counterparts. Unfortunately the manual copy-pasting is the only option, because extracting the Storyboards  into separate resources and referencing them with {StaticResource} isn’t supported.

To get a full copy of the default control style you can use either the XAML Designer (right-click the control, select Edit Template and Edit a Copy…), or search for it in C:\Program Files (x86)\Windows Kits\10\DesignTime\CommonConfiguration\Neutral\UAP{version}\Generic\generic.xaml

To spare your Ctrl , C  and V  keys, I have prepared the full modified style which you can take and use in your app. You can get this style here on my GitHub along with the full sample project for this article. Beware that this style targets the Anniversary Update. I recommend doing the changes manually if you target a different version.

Summary

The CommandBar  is a great control that works as we expect most of the time. When we hit an issue however, its template is quite easy to modify.

How to add new preview devices to the XAML Designer

The Visual Studio XAML Designer for Universal Windows Platform offers design-time device previews for several different screens size and scaling combos. Unfortunately, the default selection might not be sufficient for you in some cases, especially when you want to optimize for a specific screen. Is it possible to expand the selection with more devices?

Default device offering in Visual Studio

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Tip: Curly brackets in XAML Binding’s ConverterParameter

While working on an UWP app, I wanted to create a string.Format  based value converter, so that I could provide a format string in the ConverterParameter , augment the data bound value with it and use the result as a key for a localized string from resources. When I tried to build the project however, I was met with the following cryptic error message:

Although the nor the error nor the generated diagnostic were too helpful, because I have mostly added just the new XAML binding, I suspected the error must be hidden there.

As you might expect, it is not possible to use curly brackets directly inside the XAML binding expression.

Solution is simple – escaping with backslash.

With this little change, the code will compile and the value converter works as expected.