[wpf] The name does not exist in the namespace error in XAML

Using VS2012 working on a VB.NET WPF application. I have a simple MusicPlayer tutorial app I am using to learn WPF. I am converting a C# version of the tutorial to VB.NET step by step.

It has 2 classes in the app that are both under the same namespace. I am able to reference the namespace in the XAML but when I try to reference the class object in XAML I get an error and I am not able to compile.

Strange thing is that the IntelliSense works fine with both referencing the namespace via the xmlns:c= tag and also when typing the class object using <c: But the object is underlined and errors are generated trying to build or work in the designer.

The .vb class files are in a folder called \Controls. The Main project Root Namespace is intentionaly left blank. The class is coded like this...

Namespace MusicPlayer.Controls
    Public Class UpdatingMediaElement
       .... code here
    End Public
End Namespace

The xaml looks like this

(namespace defined in the <Window > tag

xmlns:c="clr-namespace:MusicPlayer.Controls"

(object defined in a <Grid> )

  <c:UpdatingMediaElement Name="MyMediaElement" />

(error displayed) The name "UpdatingMediaElement" does not exist in the namespace "clr-namespace:MusicPlayer.Controls".

Not sure what is wrong or how to fix it?

In my case it was because of other compile errors. When other errors have been solved this seemingly related error was also removed from the list. Specially the errors at the bottom of the errors list and on pages you have recently changed.

So do not pay attention to this error directly and focus on other errors at first.

• In my particular case, the problem looks like a bug in Visual Studio - because the error didn't make any sense! This is what worked for me: perhaps it may work for you as well?

Solution: Try Re-building the solution

• Short cut to re-build: CTRL + SHIFT + B

The same problem plagues Visual Studios 2013, Service Pack 4. I also tried it with Visual Studios 2015 Preview with the same results.

It's just a limitation of the WPF visualizer which the Visual Studios team hasn't fixed. As proof, building in x86 mode enables the visualizer and building in x64 mode disables it.

Strangely enough intellisense works for Visual Studios 2013, Service Pack 4.

Also try to right click on your project->properties and change Platform target to Any CPU and rebuild, it will then work. This worked for me

If non of the answers worked

For me was .Net Framework version compatibility issue of the one i'm using was older then what is referencing

From properties => Application then target framework

I went through all the answers and none helped me. Finally was able to solve it by myself, so presenting the answer as it might help others.

In my case, the solution had two projects, one containing the models (say the project and assembly name was Models) and another containing the views and view models (as per our convention: project, assembly name and default namespace were Models.Monitor). The Models.Monitor referred Models project.

In the Models.Monitor project, in one of the xaml I included the following namespace: xmlns:monitor="clr-namespace:Models.Monitor"

I suspect that MsBuild and Visual Studio then were erroring out as they were trying to find a 'Monitor' type in the assembly 'Models'. To resolve I tried the following:

1. xmlns:monitor="clr-namespace:Models.Monitor;assembly=" - which is valid if the namespace is in same assembly as per https://msdn.microsoft.com/en-us/library/ms747086(v=vs.110).aspx
2. also tried the explicit namespace declaration: xmlns:monitor="clr-namespace:Models.Monitor;assembly=Models.Monitor"

Neither of the above worked.

Finally I gave up, and as a work around moved the UserControl I was trying to use to another namespace: 'ModelsMonitor'. I was able to compile fine after that.

Try checking the References section, and see if there is a warning icon over the library reference you included:

If you see it then go to the Project -> Properties -> Application and make sure that both libraries are targeting the same version of the .NET framework.

P.S. When this issue happens it can also be noticed from the Warnings section:

If the assembly is different from the namespace in which your class is contained, you have to specfiy it explicitly.

ex:-

xmlns:Local="clr-namespace:MusicPlayer.Controls;assembly=MusicPlayer"

Dunno if this will help anyone else

I'm new to WPF and still a novice with VB.net - so I was assuming that getting this error was being caused by me doing summit silly........ suppose I was really! I've managed to get rid of it by moving my project from a shared drive to one of my local drives. Error's disappeared, project compiles perfectly no further issues - yet. Looks like VS2015 still has problems with projects held on a shared drive.

I had the solution stored on a network share and every time I opened it I would get the warning about untrusted sources. I moved it to a local drive and the "namespace does not exist" error went away as well.

This problem can also be caused if the assembly that you're referencing isn't actually built. For example, if your xaml is in Assembly1 and you're referencing a class also in Assembly1, but that assembly has errors and isn't building, this error will be shown.

I feel silly about it, but in my case I was tearing asunder a user control and had all sorts of errors in the related classes as a result. As I was attempting to fix them all I started with the errors in question, not realising that xaml relies on built assemblies to find these references (unlike c#/vb code which can work it out even before you build).

I'm also having a lot of trouble with this one! Intellisense helps me complete the namespace and everything, but the compiler cries. I've tried everything I found in this and other threads. However in my case what helped in the end was writing something like this:

xmlns:util="clr-namespace:LiveSpielTool.Utils;assembly="

Leaving the assembly name empty. No idea why. But it was mentioned here. I must add I am developing an assembly, so the assembly attribute might make sense. But entering the assembly name did not work. So weird.

I had the same problem , and in my case the the Markup Design View asked me to rebuild the solution and did not show me the form layout with this message: Design view is unavailable for x64 and ARM target platforms, or Build the Project to update Design view.

It does not get solved by rebuilding the solution (neither the design view nor the "The name does not exist in the namespace" error)

I think it was because I had played with the settings on Solution -> Properties > Configuration Properties

I finally resolved the problem with 2 jobs:

1. Checking all check boxes on Build Column of the page: Solution -> Properties -> Configuration Properties
2. Changing the solution configurations from Debug to Release or vice versa.

I think it's a bug in Visual Studio2012 Update 2.

Jesus... This is still a problem five years later in Visual Studio 2017. Since I'm new to WPF, I was sure the problem was somehow me, but no, everything compiled and ran correctly.

I tried rebuilding, cleaning and rebuilding, switching between x86/x64 output, rebooting Windows, cleaning the ShadowCache folder, adding ";assembly={my main assembly name}" to the XML namespace declaration, nothing worked! The single thing that did:

Put my static class of Commands (in my case the deal was about making the design discover my WPF Commands) in its separate assembly and changing the assembly name to that one's instead.

This happened to me already twice in a complex WPF app, in it there are 4 multi platform projects, 1 shared project, 2 support libraries, and 1 test project..

This very specific XAML namespace error happened twice on very recently modified files on the Shared project. In both of my cases, it was a new c# file added with a repeating namespace entry;

Like namespace MyProgram.MyFolder.MyProgram.MyFolder

I double pasted it once by mistake, and once it was due to JetBrains Rider double pasting the namespace. (If you ever rename a project in Rider, it time to time starts double pasting namespaces on new file creations, especially on Shared projects..). These c# files with repeating namespaces were then called in the ViewModels where XAML files were referencing to. Well you then get these unrelated and misleading errors, you can have a problem with one file, all your Xaml files will start erroring out eventually.

Anyways, if you get these kind of errors, it's most of the time an issue on a very newly added file or code change. My suggestions would be to look at your very recent changes.

Add an empty constructor for your view model and rebuild solution.

Another possible cause: A post-build event is removing the project DLL from the build folder.

To clarify: WPF designer may report "The name XXX does not exist in the namespace...", even when the name does exist in the namespace and the project builds and runs just fine if a post-build event removes the project DLL from the build folder (bin\Debug, bin\Release, etc.). I have personal experience with this in Visual Studio 2015.

Try verifying your assembly references. If you have a yellow exclamation mark on the project references there's a problem there and you'll get all kinds of errors.

If you know the project reference is correct, check the Target framework. For instance, having a project using the 4.5 framework reference a project with 4.5.2 framework is not a good combination.

Looks like this problem may be solved through a variety of "tricks."

In my case, I had been building/rebuilding/cleaning the entire solution, instead of just the project that I was working on within the solution. Once I clicked "Build [my project]," the error message went away.

The solution for me was to unblock the assembly DLLs. The error messages you get don't indicate this, but the XAML designer refuses to load what it calls "sandboxed" assemblies. You can see this in the output window when you build. DLLs are blocked if they are downloaded from the internet. To unblock your 3rd-party assembly DLLs:

1. Right click on the DLL file in Windows Explorer and select Properties.
2. At the bottom of the General tab click the "Unblock" button or checkbox.

Note: Only unblock DLLs if you are sure they are safe.

Maybe another solution for when the project compiles but the XAML error is showing :

1. In solution explore, on the project node that contains the xaml
2. Right-click on the project and choose 'Unload Project'
3. Right-click on the project and choose 'Reload Project' Make sure that your project is still choosen as "startup project". If not :
4. Right-click on the project and choose 'Set as startup project'

No need to rebuild, or close visual studio.

In Visual Studio 2019 I was able to fix it by changing the dropdown to Release as recommended in other answers. But when I changed back to Debug mode the error appeared again.

What fixed it for me in Debug mode:

1. Switch to Release mode
2. Click on "Disable project code" in the XAML Designer

3. Switch back to Debug mode => the error is gone

Adding to the pile.

Mine was the assembly name of the WPF application was the same assembly name as a referenced dll. So make sure you don't have duplicate assembly names in any of your projects.

In my case, the user control was added to the main project. I tried various solutions above to no avail. Either I would get Invalid Markup but the solution would compile and work, or I would add the xmlns:c="clr-namespace:MyProject;assembly=MyProject" and then the markup would show, but I would get a compile error that the tag does not exist in the XML namespace.

Finally, I added a new WPF User Control Library project to the solution and moved my user control from the main project into that one. Added the reference and changed the assembly to point to the new library and finally the markup worked and the project compiled without error.

Try changing the build target platform to x86 and building the project.

I noticed via Subversion that I apparently changed the project build Platform target to x64. This was the only change I had made. After making that change, the code was working for a short while before it started showing the same error you experienced. I changed the platform target to x86 to test and suddenly my designer was working again. Subsequently, I changed it back to x64, and the problem has disappeared completely. I suspect that the designer builds some kind of cached code in x32 and changing the x64 build platform breaks it when you make code changes.

Ok, so none of these tips worked for me, unfortunately. I was able to eventually solve the issue. It seems that Visual Studio does not play nicely with network drives. I solved this issue by moving the project from the shared drive to my local and recompiled. No more errors.

I've seen this issue go away by clearing the Xaml Design Shadow Cache. I had the issue with Visual Studio 2015 Update 1.

In Visual Studio 2015 the Cache is located here:

%localappdata%\Microsoft\VisualStudio\14.0\Designer\ShadowCache

Process:

1. Right-Click on the solution in the Solution Explorer and Choose "Clean Solution"
2. Shutdown Visual Studio
3. Delete the ShadowCache folder
4. Reopened the Visual Studio project
5. Rebuild the solution

And voila no more namespace errors.

I had the added the assembly as a project - first deleted the ddl that was added specifically to the references to the dll - that did it.

I had the same symptoms "The name does not exist in the namespace error", but the cause turned out to be different. I had a C: drive crash and had to reinstall Visual Studio 2017. I restored my source code files and opened the solution. Built it. No dice. As well as the "Name does not exist in the namespace" errors I noticed my sub-projects complaining that they couldn't find a MyProject.cs file ('MyProject' is not the actual project name, just used here as an example). I had a hunt for where MyProject.cs had gone, then remembered that there was never any such file! I looked in the Properties folders of each sub-project and found that Visual Studio had off its own back added bogus references to MyProject.cs!! I removed these references and now the solution builds fine like it used to.

In my case the problem was due to some phantom files under the project's obj directory. The following fixed the issue for me:

• Clean project
• Exit VS
• rm -rf /obj/*
• Invoke VS and rebuild

I get this problem all the time. My views are in a WPF Custom Control Library project (a variant on Class Library). I can reference pre-built assemblies, but cannot reference any code in another project of the same solution. As soon as I move the code to the same project as the xaml it's recognized.

In my case, this problem will happen when the wpf program's architechture is not exactly same with dependency. Suppose you have one dependency that is x64, and another one is AnyCPU. Then if you choose x64, the type in AnyCPU dll will "does not exist", otherwise the type in x64 dll will "does not exist". You just cannot emilate both of them.

In the solution property page, check the platform of the assembly that contains "UpdatingMediaElement" and the assmeblies that contain any of the superclasses and interfaces from which "UpdatingMediaElement" subclasses or implements. It appears that the platform of all these assemblies must be "AnyCPU".

VB.NET does not automatically add the Namespace information based on the folder structure as it does in C#. I think I am going through the same tutorial as you (Teach Yourself WPF in 24 Hours), and doing the same conversion to VB.

I found you have to manually add the Namespace information to Both the XAML Class and the XAML.VB code behind to be able to use the Namespaces as described in the book. Even then, VB doesn't automatically Assign the Namespace to the Assembly as it does in VB.

There is another article here that shows how to include this in your project templates so it does build the Namespace information automatically - Automatically add namespace when adding new item

In my case I had a namespace and class spelled exactly the same, so for example, one of my namespaces was

firstDepth.secondDepth.Fubar

which contains its own classes (e.g. firstDepth.secondDepth.Fubar.someclass)

but I also had a 'Fubar' class in the namespace

firstDepth.secondDepth

which textually resolves to the same as the Fubar namespace above.

Don't do this

I had this problem recently using VS 2015 Update 3 for my WPF project in .NET 4.6.2. The copy of my project was in a network folder, I moved it locally and that solved the problem.

This may solve other sort of problems, as it looks like VS 2015 doesn't like network paths. Another issue that is a big problem for them is syncing git repositories if my project is in a network path, also solved by moving it locally.

A combination of two ideas in this thread worked for me, so I'll post what I did in the hopes that it helps someone else over the next 5 years that this problem continues. I'm using VS2017 Community)

1. Delete reference to dll
2. Clean, Rebuild, Build
3. Close VS, Unblock the dll (see note below), Delete shadow cache
4. Open VS, Clean, Rebuild, Build
5. Restore reference to dll
6. Clean, Rebuild, Build

I may not have the order exactly right in steps 2, 4, and 6 but I was grasping at straws after spending nearly 2 hours with this problem. I think the key for me was the combination of removing the reference, unblocking the dll and deleting the shadow cache.

(Note for step 3 - The dll I'm using was written by a coworker/mentor of mine, so I know it's safe. Careful with this step if you don't know the source of your dll)

I'll be bookmarking this thread for posterity, since it appears that MS has no desire to clean this stuff up. WPF is hard enough to learn on it's own, and having to hack through stuff like this when you've done everything right is infuriating.

As another person posted this can be caused by saving the project on a network share. I found that if I switched from using a network path to a mapped network drive everything worked fine.

from: "\\SERVER\Programming\SolutionFolder"

to: "Z:\Programming\SolutionFolder" (exact mapping optional)