Develop Reference

Unable to Resolve Resources

I am using the MaterialDesign for XAML package in WPF. When I run my application, all styles and controls are rendered as expected. However in the XAML designer I have dozes of errors such as "The resource 'MaterialDesignFlatButton' could not be resolved." Example of a line that is throwing that error:
<Button Style="{StaticResource MaterialDesignFlatButton}" IsDefault="True" Margin="0 8 8 0" ...
My app.xaml contents is as follows:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml" />
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
<ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Primary/MaterialDesignColor.Blue.xaml" />
<ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Accent/MaterialDesignColor.LightBlue.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
I have attempted the top solution proposed on The resource "x" could not be resolved. but that causes the project to fail to run (I believe I am not using the correct pathing when attempting to use the proposed "absolute pack URI"). So I have two questions at this point:
Is there a reason the resources would fail to resolve in the XAML designer given the way I have defined them in App.xaml (per the developer guide: https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/wiki/Getting-Started)?
How can I find out the "absolute pack URI" to use for the source for my resource dictionaries?

In the past, I had problems like this.
The error causes are as follow.
1. Setup and setting config
About this, please check the github and material design homepage.
2. Build and Compiler problem
About this, users may set the "Platform Target" as "x64".
That can invoke errors because material designer tool use "x32" compiler, so please use "any cpu" or "x32".

I had this problem with the flat accent button, while every other button style worked. I added the resource for buttons, then the error was gone. Then I removed the button resource... and the error was still gone.
https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/wiki/FAQ
Exception: Cannot find resource named 'MaterialDesign...'
This error typically comes when you have a static resource referencing
one of the material design styles, and have not included the
appropriate resource dictionary that contains the style. Try the
following:
Ensure that you have loaded all of the default material design styles in your App.xaml. You can find directions for this in the
Getting Started guide.
Ensure you have referenced the control specific resource dictionary that contains the style. The path for this is resource dictionary
should be .xaml" />. For example, if you were trying to reference the
MaterialDesignFloatingActionMiniButton style for a button, the
resource dictionary source would be: . Typically these inclusions are done at root of your Window, User
Control, or Template. You can find the full list of the resource
dictionaries here

ResourceDictionary.MergedDictionaries causes weird errors

Inside my WPF Application I am including a ResourceDictionary from another Project.
<Application x:Class="namespace.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<!-- This Line causes an Error -->
<ResourceDictionary Source="pack://application:,,,/Commons;Component/Generic.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
Metadata override and base metadata must be of the same type or derived type.
The solution builds successful and runs.
Restarting Visual Studio doesn't fix it.
Cut and Paste the <ResourceDictionary Source="..." /> line causes another error as explained here in the Comments:
Value Cannot be Null. Parameter Name: item. Restarting Visual Studio will then bring back the old error.
Sadly I haven't found out how to reproduce this error, I can only tell you something more about the environment im using:
Visual Studio 2015 Professional, Version 14.0.25431.01 Update 3
And allthough I doubt, those are associated with my problem, here my installed Plugins:
Resharper Ultimate 2017.1.1
GitExtensions Version 2.49.03

Sinatr's comment hinted me to read more about theming.
ThemeInfo
Inside of a Custom Control Library theres automatically created a ThemeInfoAttribute inside AssemblyInfo.cs
[assembly:ThemeInfo(
ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located
//(used if a resource is not found in the page,
// or application resource dictionaries)
ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located
//(used if a resource is not found in the page,
// app, or any theme specific resource dictionaries)
)]
Parameters
As it states in the autogenerated comments, the first parameter is to determine wheter there exist or where to find Theme specific resource dictionaries.
The second parameter defines wheter there exist or where to find the generic ResourceDictionary (Generic.xaml).
ResourceDictionaryLocation-Enumeration
The ResourceDictionaryLocation-Enumeration itself is used to specify the location of those dictionaries.
ResourceDictionaryLocation.None
No theme dictionaries exist.
ResourceDictionaryLocation.SourceAssembly
Theme dictionaries exist in the assembly that defines the types being themed.
This expects the ResourceDictionary to be located in a /Themes-Folder. Explanation later.
ResourceDictionaryLocation.ExternalAssembly
Theme dictionaries exist in assemblies external to the one defining the types being themed.
I am not going to explain how this works.
Why /Themes-Folder
Sadly I couldn't find too much about this. If someone has some more info please share.
Have you ever wondered, how styles of a lookless control are being applied?
If one created a lookless Control, he did as follows:
public class MyControl : ControlTemplate
{
static MyControl()
{
// This tells WPF to search for a Style for this type
DefaultStyleKeyProperty.OverrideMetadata(typeof(MyControl)),
new FrameworkPropertyMetadata(typeof(MyControl)));
}
}
In short, Ressources in WPF are located, by searching up the Logical-Tree, then inside Application's Resources and finally inside sth. they call System-Area (this is my translation from German, if you know a better one pls tell).
So depending on ThemeInfo, MyControl propably had its Style inside a ResourceDictionary inside the /Themes-Folder, eg. /Themes/Generic.xaml. And that tells WPF to add the Ressources to the System-Area which finally results in automatically resolving the appropriate style.
Somewhere inside /Themes/Generic.xaml:
<Style TargetType="{x:Type MyControl}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type MyControl}">
..
</ControlTemplate/>
</Setter.Value>
</Setter>
</Style>
That's why the above ThemeInfoAttribute requires Generic.xaml to be located in a /Themes-Folder. - And somehow, even if in my case the System-Area-Functionality isn't even used for this generic file, this causes those errors. But I wasn't able to find out why.
Sources:
ThemeInfoAttribute Constructor
ResourceDictionaryLocation Enumeration
Windows Presentation Foundation - Das Umfassende Handbuch, Rheinwerk Computing Version 4

XAML Forms not recognizing local and referenced classes

I opened a VS 2012 Solution in VS 2015 and cannot get it to compile. It was originally targeting .Net 3.5 and used the WPF Toolkit, which caused some ambiguous references. I resolved that by removing the reference to the WPF Toolkit and replacing it with the package DotNetProjects.Wpf.Toolkit.
Now I have to tackle the next issue, which I suspect is not caused by the obvious but is a cascade from some other hidden gotcha from upgrading the versions.
My XAML forms are not recognizing the existence of classes within referenced namespaces. I can get them to come up on intellisense but the application won't compile and the error says something like: "The name "MainWindow" does not exist in the namespace "clr-namespace:FieldSheetPrinter".
I have defined my main form with the following:
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:FieldSheetPrinter"
mc:Ignorable="d"
xmlns:Custom="http://schemas.microsoft.com/netfx/2009/xaml/presentation"
xmlns:validationRules="clr-namespace:SWallTech.ValidationSupport;assembly=SWallTech.ValidationSupport"
xmlns:FieldSheetPrinter_Converters="clr-namespace:FieldSheetPrinter.Converters"
xmlns:Converters="clr-namespace:SWallTech.WPF.Support.Converters;assembly=SWallTech.WPF.Support"
x:Class="FieldSheetPrinter.MainWindow"
x:Name="MainWindow"
Title="CAMRA Field Sheet Printer - Stonewall Technologies, Inc."
Width="744"
Height="583"
WindowStartupLocation="CenterScreen"
Icon="CamraPrint.ico">
I have references to the SWallTech.WPF.Support project, which is in the solution, and the compiler has no problem recognizing the classes in that project's Converters namespace. This code has no error indicator. (Red squiggles.)
<Converters:IntGreaterThanZeroToVisibilityConverter
x:Key="IntGreaterThanZeroToVisibilityConverter" />
<Converters:DatabaseConnectionImageSourceConverter
x:Key="DatabaseConnectionImageSourceConverter" />
However if I try to refer to the ViewModel I am using as the datasource, I get an error:
<local:FieldSheetPrinterViewModel
x:Key="FieldSheetPrinterViewModelDataSource"
d:IsDataSource="True" />
I also get the error that the XAML form itself is not in the namespace FieldSheetPrinter, which of course it is, as you can see from the Code-Behind.
namespace FieldSheetPrinter
{
public partial class MainWindow : Window
...
}
I have tried everything I can think of, and I am truly stumped.
Joey

As suggested above, the problem wasn't directly with the XAML, or at least not completely. The original developer had named the Window tag with the same name as the code-behind class name, and that seems to be prohibited now. That was the only issue with the XAML. Everything else had to do with overlaps in the WPF and Windows.System.Data libraries that caused IValueConverter (in the System.Windows.Data namespace) to go unrecognized. I eliminated any other references that could have conflicted, and corrected some syntax issues in the code-behind that apparently were deprecated.
Ex.
stringVariable.IsNullOrEmpty()
was used instead of
string.IsNullOrEmpty(stringVariable)
In other places some ObservableCollection objects weren't recognized as enumerable, so I had to add "ToList()" before looping through the collection.
Weird, but I didn't write this stuff!
Thanks for the suggestions.
Joey

WPF MergedDictionaries - Value Cannot be Null - Parameter Name: item

I am having a nagging issue with my App.Resources MergedDictionary. Every time add a new dictionary with a source and XML namespace from another assembly, an error is produced and I cannot build my program.
The error appears in App.xaml with the ResourceDictionary underlined and the message Value Cannot be Null. Parameter Name: item. This makes absolutely no sense as I have done the exact same thing before. The only difference is that this time, I am referencing the namespace of another assembly(c# class library). Here is the App.xaml file:
<Application x:Class="Quiz.Client.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Quiz.Client"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Resources/Styles.xaml" />
<ResourceDictionary Source="Resources/Templates.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
Below is Styles.xaml:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Quiz.Client">
<Style x:Key="StrongFont"
TargetType="ContentControl">
<Setter Property="FontSize"
Value="20" />
<Setter Property="FontWeight"
Value="ExtraBold" />
<Setter Property="Foreground"
Value="DarkRed" />
</Style>
</ResourceDictionary>
Here is Templates.xaml:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Quiz.Client"
xmlns:domain="clr-namespace:Quiz.Core.Domain;assembly=Quiz.Core"
xmlns:common="clr-namespace:Quiz.Client.Common">
<DataTemplate x:Key="ArithmeticQuestionTemplate"
DataType="domain:ArithmeticQuestion">
</DataTemplate>
<common:QuestionTemplateSelector x:Key="QuestionTemplateSelector"
ArithmeticTemplate="{StaticResource ArithmeticQuestionTemplate}" />
</ResourceDictionary>
What the heck is going on? Was there a software-breaking change introduced or something? I am completely lost.

Confirm!!! This bug is tracked by Microsoft. This mean WPF in some points will is trying to report to Microsoft automatically with Microsoft report process. During the report VS start freeze. Please, wait bug report to finish.
The bug still exist in lattes VS 2019.
After restart everything is fine. Confirm!!!
Thanks for the answer. I believe it is a Visual Studio bug caused by something unknown. Maybe one of my plugins, who knows. The only thing that fixes the issue is restarting visual studio and building the project. The problem seems to begin when adding a new namespace from another assembly. The project then can't build until visual studio is restarted. Very weird, never seen anything like it before. – user3096803

Not sure why your method isn't working but it's not how I usually import resources myself. Typically I'll add a ResourceDictionary to my library project, put all the libraries resources in that and import it into my main project using pack syntax:
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="pack://application:,,,/MyLibrary;component/LibraryResources.xaml" />
</ResourceDictionary.MergedDictionaries>
<!-- main project resources go here -->
</ResourceDictionary>
In general I'd argue that this is a better architecture anyway as it doesn't require a re-compile of your main project each time one of the child library resources change. It also makes it easier later on if you decide to switch to MEF, as your library resources are now encapsulated in a single ResourceDictionary object that you can readily [Export].

I don't really understand the answer from #Pit but I tried restarting visual studios and also changing all source paths to full pack URIs, and nothing seemed to work. Came across this thread that hinted at using Tools > Options > Preview Features > New WPF XAML Designer for .NET Framework which fixed the issue for me.
EDIT: This "fix" may have been a red herring, it still had issues but they were equally cryptic! After switching back to the old XAML designer and doing some further digging I found that one of my merged dictionaries was incompatible with the wpf designer and it was resulting in this error. The fix on that page resolved my issue.
This specific fix probably won't help anyone, but hopefully the methodology will. Check if there are any errors in any of the individual resource dictionaries in the merged dictionaries.

Problems with adding EnumMatchToBooleanConverter to my xaml file

I am trying to follow this radiobutton tutorial
I created a class called EnumMatchToBooleanConverter and it is in the top level of my wpf project. It says to place the inside a window.resources like this:
<Window.Resources>
<EnumMatchToBooleanConverter x:Key="enumConverter" />
</Window.Resources>
I am using it in a usercontrol so I have placed it inside a stackpanel instead:
<StackPanel.Resources>
<EnumMatchToBooleanConverter x:Key="enumConverter" />
</StackPanel.Resources>
I have Microsoft Visual Studio Ultimate 2012 and it gives me an error:
EnumMatchToBooleanConverter is not supported in a Windows Presentation Foundation (WPF) project.
Any ideas as to what I am doing wrong? Am I not allowed to place it inside a stackpanel.resources?
I just tried placing it inside a grid.resources
<Grid.Resources>
<EnumMatchToBooleanConverter x:Key="enumConverter" />
</Grid.Resources>
and it says
The type 'EnumMatchToBooleanConverter' was not found. Verify that you are not missing an assembly reference and that all referenced assemblies have been built.
Well it is in the same namespace as the rest of my project, so I'm unsure why it isn't finding it.

Change
<EnumMatchToBooleanConverter x:Key="enumConverter" />
for
<local:EnumMatchToBooleanConverter x:Key="enumConverter" />
All non-built-in classes you reference in XAML must be prefixed by their corresponding xmlns prefix.

HighCore's got it right. Just to add to this namespace discussion, I thought I'd point out another approach that can help make the code more readable or help you diagnose where certain Controls/Value Converters/etc are coming from (i.e., which assembly they are really coming from). This technique could allow your XAML to appear like Christian has it in his blog (without the xmlns prefix):
<EnumMatchToBooleanConverter x:Key="enumConverter" />
Essentially you perform some some namespace mappings to consolidate namespaces like this (only works if the files are in a different assembly/project). So in my example above you have mapped one of your namespaces to the default xmlns, so you would not need any prefix in the XAML.
I'm still trying to figure out how far to take this technique and Paul Stovell talks about taking it to the extreme, like I've shown above.
Even if you don't end up applying it to that degree, knowing about it might come in handy if you're looking at someone else's Xaml and they have applied a mapping like that. Knowing that would remind you to lookup the AssemblyInfo.cs file and check for the mapping and possibly help you track down where a Control/Value Converter/etc is actually located.