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Visual Studio 2015 - Xamarin - Android - Getting "resource.id does not contain a definition for xxx" when I try to do anything in the .cs file

Adding Additional Activity .cs and Layout axml Using Visual Studio 2015.
I'm very new to Xamarin and Android development, but have been a developer for a few years using VB and now C#. I have a simple app on Android 4.2 that is getting more complicated as I go along. The simple matter us that I want to add an additional GpsAction.cs and corresponding Gps.axml layout to the project. It seems impossible to find the right combination syntax to achive this. I have a mainActivity with main.axml. In VS 2015 it's very simple to add new but I keep getting "resource.id does not contain a definition for" I would really appreciate your help with this
namespace AddCam
{
[Activity(Label = "GpsActivity")]
public class GpsActivity : Activity
{
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.GpsLayout);
string c = FindViewById<TextView>(**Resource.Id.textView1**).Text;
// Create your application here
}
}

For people who are still facing this issue, the default Build Action of the layout file would be set to TransformFile. Select the layout, go to the Layout Properties, and in the properties pane, Select AndroidResource as your Build Action. Clean build your project and it should work.

I changed the text field "id" from "#+id/imageView1" to "1", saved, rebuilt and changed it back to "#+id/imageView1", it fixed it. I would like to add, this whole problem came from
Adding a new activity and layout.
Using preexisting code from another app that I had.
Copying and pasting code from the original app to the new Activity
and Layout.
All fairly common stuff, the real problem seemed always to be adding any new Activities and Layouts to a main Activity. It can get very convoluted and with no (known to me) logical way to run down a problem with Xamarin. Don't get me wrong compared to 10 years ago (the last mobile app I tried to write) Xamarin is heaven. Good coding folks, now if I can only figure out why Keyword "this" is error-ring on the added Activity.cs

Just add namespace like that Android.Resource.Id - it's resolve for me

What did work for me (Visual Studio 2017, opening an old Xamarin project):
Delete obj and bin folders, build.
If errors, restart Visual Studio (I know the pain).
Build again
Now the Resource will be visible (of course, if you defined it correctly).

The best solution I have found is to build solution.
Choose Build solution from Build menu (or Ctrl+Shift+B).
This action will resolve the issue.

You Should add set value forandroid:id="#+id/button1" in axml of app, then rebuild the project and try again.
like thisButton button = (Button)FindViewById(Resource.Id.button1); .

Check if you are missing these namespaces in your layout file -
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"

(VS 2019) I did the previous solutions and nothing, I had the same problem and the solution for me was to remove '&' from the text of TextView, I was trying to Set the text to "text&text" even &&(I though it was like mnemonics as in WindowsForms) didn't work so I had to remove it and it fixed.

Cleared Main.axml page and Reset and it is working.

My problem was I was trying to debug Xamarin Android project (native) using Xamarin Live Player, connecting using USB cable and selecting my device for debugging solved the problem

Make sure your axml is well formed and rebuild the solution it should work, if you continue facing the same issue then remove axml and add it again then build the solution.

In Visual Studio 2019 when you add a new Android Layout to the Project it is added as .xml file. I already had some created earlier layouts in Resources/layout folder with extension .axml (not .xml) and for me changing the extension .xml -> .axml worked.

I understand that this issue is very old, but I've run into it as well in Visual Studio 2019, and have found a solution.
The issue occurs, for me, when adding an element to the layout and then attempting to add code. The issue appears to be related to the way the project is built.
Add the element to your layout, then build your project before adding any additional code. Apparently Resource.Id does not update with additional members until it's built, and attempting to refer to the new member in the code before Resource.Id recognizes it prevents the project from being built.

Like Maniacz said, in VS 2019 I just had to change the XML to axml extensión to the layout in layout folder under resources

For anyone else looking for an answer despite running clean/build/rebuild which didn't work for me:
I had freshly installed a number of tools for xamarin development in VS. Though a build/rebuild may have actually worked, in my case I believe what also fixed it was closing and re-opening VS. I'm pretty sure I had a few issues, primarily stemming from newly installed tools (android SDKs in my case) requiring VS to be restarted. If you're working on a project already having installed the tools you need, try as others have said - build/rebuild.

I had to modify Build Action for my layout file and re set the original Build Action as it was previously set. This made my visual studio to regenerate the resource ids in Resource.designer.cs file.
Step #1:
Go to properties of the layout file that is missing its ids and click the Build Action DropDown.
Step #2:
Select something from the dropdown other than AndroidResource.
Step #3:
Reselect AndroidResource from that Build Action.
Now, you will have your Resource.designer.cs file regenerated and it will have the reference ids to your controls in the layout file.

Check the Resource.Designer class file. There will be a class like public partial class Id. There the integer IDs of the controls are written. Use them instead of Resource.Id

WPF Project with Custom XAML Controls

I am new to WPF coding. I have a project that has custom controls coded as xaml's with C# code-behinds. I try to import these files into another project and when I try to use these xaml controls in my main view file, Visual Studio cannot find the namespace that the imported xaml's and C# code-behinds are attached to.
I tried changing the namespace to be the same as my current project. I tried restarting Visual Studio 2013. Neither of these worked.
I tried adding the project with the custom controls to my solution. The imported project can read the custom xaml's, but my main project still can't reference them. I tried dragging the files over to the main project, and they still won't work.
I tried rebuilding the controls xaml's and C# code-behinds in my new project it still says:
The type 'local:ClickSelectTextBox' was not found. Please verify that that you are not missing an assembly reference and that all reference assemblies have been built.
This item is under the appropriate namespace and in the current project.

In visual studio go to TOOLS -> choose Toolbox Items. this will allow you either choose from an array of different components or browse around to find a dll that you would like to use.
EDIT:
Oh so you are trying to take customized xaml files that you already have written and modify them in a separate project? I would suggest one of two things.
1: right click your project name -> add existing, and add the xaml and xaml.cs file to your project at the same time.
if for some reason that does not work you can also try
2: creating a new xaml control (with the same name of the control you want to drop in) in your project and copy pasting the xaml code into that control, this should autogenerate the codebehind designer shell you are going to need. you can then go into the xaml.cs file and drop whatever business logic you are looking for. It is not the cleanest solution but sometimes the WPF editor gets a little funky when importing xaml files

I know it's an old post but still somebody may find it useful:) So! ... Make sure
1)You don't have public class outside of root namespace, check this
link
2)You are not mixing targets of your assemblies (unless you can't 100% avoid that)
For example, if you are referencing something like SQLite.Core NuGet (that has both x86 and x64 versions of SQLite.Interop.dll built in) in a project that is AnyCPU, sometimes it's easier to set application's target to x86 or x64 to solve the x86/x64 paths issues - but then you may get all these "type not found/control not built/assembly not found" and all that sorts of nonsense from Designer even despite your app builds and runs ok.
Hope that helps

Try downloading ReSharper's trial version, install it and then open up your code again. One of the awesome features Resharper has with XAML code is that it will automatically map objects to their appropriate namespace. I think this will make it easier for you and will show you a ton of ways to do things better. When I was first learning WPF it was honestly a godsend to use Resharper.

Failed to load toolbox item. It will be removed from the toolbox

I have a WinForm application. I also have created my own User Control for it. Everything worked fine. Until today that I received the error message when I try to add it back to my program (I never removed it. Visual Studio did).
Failed to load toolbox item #UserControlName. It will be removed from
the toolbox.
I have it in my solution explorer but it vanishes from my toolbox after this error.
I also receive the warning that says:
'#UserControlName' is never assigned to, and will always have its
default value null.
And when I look at my designer code, that is true. But I haven't done anything with my designer code. My user control is defined there but not instantiated. How can I put it back?
Does it have anything to do with the fact that I changed my build platform from x32 to x64? If that is the case I will be surprised because the program was working fine after that change.

I was suffering from the same issue for one of our applications and could not find a solution. So I created the user and custom controls manually. After searching the web again I finally found why the designer is failing for this particular project. The answer is that project is 64 bit and Visual Studio is still does not have a 64 bit version, it is still 32 bit. So the designer could not load the controls in 64 bit applications or in class libraries. Read Microsoft's article about this.
There was an article on Visual Studio web site but it was removed. See the the answer in Visual Studio support forum.
https://social.msdn.microsoft.com/Forums/vstudio/en-US/77e10b58-43cc-4aab-919f-888f14f99571/x64-class-library-of-user-controls?forum=csharpgeneral

I had the same issue lately. As this (nor any other answer on this site and on the internet) actually helped me, I found out the way to fix it.
Just clean the files and rebuild the solution. As simple as that.

I was having same issue but I find the solution:
Click on "Project_Name" with left mouse and click "Build" then you can add the UserControl to your WinForm.

Change to AnyCPU and rebuild the project.
Visual Studio has problems with controls being 64bit.

You don't have to necessarily insert the user-control manually. I had the same situation an there was a reason for it.
In my case, it failed because the EXE assembly was compiled to 'mixed-mode' by using CLR support type /clr. After changing it to 'managed-only' by setting type /clr:pure, it worked.
For details, see my answer here at SO.

After many hours of head scratching with this problem with a large custom control with few changes from a previous working copy in source control I copied all the code into a new control name and file and it all worked.
This was to identify the problem line(s) of code since the debugger would not co-operate. The copied control (along with heaps of support code and modules) worked okay.
So these are the very simple steps that fixed my original code
In solution explorer rename the file (I just added an s at the end)
Rebuild
Test the control can now be added to a plain form
Rename the control back to its original name
Step 4 might be optional for you but if you have source control and it's a in a library you would want to do this.
This brought the control back onto all my forms that weren't working (so far as I can tell). It seems the problem is in VS that somehow remembers it doesn't like it?
Hope this helps and I hope I find this message next time I get this when I have forgotten the fix :)
P.S. Clean, rebuild and/or re-run the solution is the old stand by for this problem but this time it was just one custom control in a whole (DLL) class of them. Hope this helps.

For me, after adding the userControl, I rebuild the application first then refreshed the items on the tool box by going to projects => Refresh project toolbox items

Right click - Rebuild Solution fixed it for me!

Mostly caused by 32 bit / 64 bit architecture. Before Visual Studio 2022 the VS built in 32 bit, therefore cannot show 64 bit components.
Solution 1:
Create a new solution configuration in Configuration Manager with name: "Debug_FormDesign" or anything else.
Set the Configuration to the above name for all projects and set the platform to "AnyCPU".
Now open all projects Compile settings step by step, select the above configuration and change the Compile -> Target CPU option to AnyCPU.
Close all opened windows.
Clean solution.
Restart VS.
Select the "Debug_FormDesign" configuration in toolbar as active.
Rebuild solution.
Open the form designer -> Should work now.
You can easily switch back to the default "Debug" configuration after finish with the GUI.
Solution 2:
Use Visual Studio 2022.

At times like these, you'll be forced to tinker with the designer code. As long as you don't make drastic changes in the designer code, you shouldn't break anything. To play it safe, re-instantiate the object where the other controls are instantiated (near the top of the page). The designer should fill in the blanks for properties and such.
This should also return the control to the toolbox.

Check in your form.designer file if there is a left-behind property with that type.
It happened to me several times.
After I removed that line and rebuilt the project, everything started working.

In my case it helped to manually include the header files of the created user controls at the top of the Form where these controls are to be used.

Can't change a project's Default Namespace in Visual Studio 2013

I have a solution that includes various C# projects, and I just now noticed that I can't change the default namespace on any of them.
When I go to Properties --> Application on any of the project and change the "Default Namespace" field, a fatal error dialog pops up that says:
exception of type 'system.runtime.interopservices.externalexception' was thrown
At this point Visual Studio becomes unusable, as I can't close it or leave the screen, every click or button combination I press makes the same dialog pop up. The only thing I can do is terminate VS with the task manager.

I got around it by just renaming the <RootNamespace> node in the .csproj file

Maybe you should try to do this in another way:
Ctrl-H - Find: PreviousNameSpaceName Replace: NewNamespaceName
You can also right click the namespace in code and Refactor->Rename.
What is more: you can change the names of your projects, solutions, directories - etc. Namespaces, when adding new files, are generated using these names in fact.

I had to investigate the issue in our company and I found another workaround in our case. So I think it make sense to add it here.
Possible Solution
Check if you have more than one suo-File for the project/solution and delete the one which doesn't has the ".v12.suo" naming (better delete both)
Story behind:
We still have two Visual Studio installed (2010 and 2013) and some of our developer worked recently on 2010. So they had on the file system a regular ".suo"-File. Afterwards (some weeks later) they started to use 2013 (which created a ".v12.suo"-File).
We renamed both suo files, started VS2013 (which created the v12.suo) and were able to rename the namespace without a crash. In addition we had this issue not on all solutions. I didn't see yet a pattern, but in our case it happened mostly on solution with at least two projects and referenced project-libraries.

Cannot Place User Control on Form

I've created a C# WinForms application using VS2010. I'm new to creating user controls so I created a new user control (as part of the same project).
When I rebuild the project, the new control appears in the toolbox. And when I drag the control from the toolbox onto a form, I get the following error.
Failed to load toolbox item 'TagGroup'. It will be removed from the toolbox.
This happened the only other time I created a user control as well. I've searched the web but most answers I found seemed related to having the control in a separate assembly. (Note that I found plenty of questions with the same problem I'm having.)
Can anyone suggest where I should look next?

My application need to be 64-bit. In order to use custom user controls in the designer I just added a new project to my solution. This new project use the "AnyCPU" setting and contains all my user controls.
My solution contains the following projects:
MyApp which is my main project (Windows Form Application) compiled in 64-bit and referencing my second project
MyApp.UI.UserControls (class library) is compiled for "Any CPU" and contains all my user controls
Works like a charm and it's clean
By the way, there is a Microsoft support article about that issue.
Action: You attempt to use a 64-bit component within the Microsoft Visual Studio Integrated Development Environment (IDE).
Error cause: This behavior is by design. Visual Studio is a 32-bit process, and therefore can only execute 32-bit modules. While Visual Studio allows you to add a reference to a 64-bit assembly, it cannot actually JIT compile it to 64-bit and execute it in process.
Resolution:
Rebuild the assembly using the "AnyCPU" setting. This would allow
the component to run within a 32-bit process (such as Visual
Studio), or in a 64-bit process.
Add the assembly as a reference and load the control dynamically at
run-time. Although you still would be unable to use the
control within any designer inside Visual Studio, you can still
write the code needed to instantiate the control and set it's
properties accordingly.
Source: http://support.microsoft.com/kb/963017

I finally figured this one out.
The project I'm working with uses two class-library assemblies. Although these have nothing to do with the control I'm discussing, I looked and saw both libraries have Platform Target in the Properties|Build tab set to "Any CPU".
On the other hand, my application had this setting set to "x64". By changing my application's setting to "Any CPU", I can now place my user controls onto my forms.
Go figure...

I had this problem too, but the answer couldn't fit for me. My project has some issues it can only target x86 and x64 separately. In other words, I can't use AnyCPU configuration (that's because I reference different libraries for each configuration, since those libraries are not fit to AnyCPU).
The solution I came up with was: when I need to use the form designer, I change the setting to x86. Do the job, then set back to x64 and test. The problem occurs only with the designer, but the solution builds and runs fine.

I had this problem in VS2015 and the solution turned out to be simple.
I had created a user control by cutting and pasting a few existing controls from a form (with the aim of grouping them into the custom control). The custom control was okay (no compile errors), however the removal of the controls from the existing form meant that the application wouldn't compile. Of course not being able to add the new control meant that I couldn't update the code referencing the previous controls with code referencing the custom control.
All I did was hack and slash (commenting-out, creating temporary controls, etc.) so that the entire application would compile. After it compiled I found that I could drag the custom control onto the form (without the error that prompted this question). I then had to unhack and unslash so that the code properly referenced the new custom control.

Same problem here. I am guessing it is related to the fact that the VS2010 installed on x64 OS is still a 32bit program in the heart.
An alternative solution one might want to try is simply open TheFormThisUserControlIsSupposedToBeAddedTo.Designer.cs and use code to add the user control. Basically, you are doing the dirty work that the Designer is supposed to do.
It is not as difficult as it sounds, esp. considering that there are probably plenty of sample code in that file already (e.g. the buttons you added using Designer). The only difficult part is figuring out the right coordinates in the form to place the control.
The end result is that you can not see the user control in Desinger, but they are added on debugging/running.

I also experienced this problem but the cause was different. In my case a component (form) constructor or Load event invoked a method elsewhere that used reflection to find all classes that implemented a certain interface.
While that works fine at runtime, it generated the above mentioned exception at Design Time. (Type Initialization exception with a Type Load Exception as inner exception).

An hour of confused, weary troubleshooting at 3:36AM is again easily resolved with a fresh mind the next day!
I fixed a simple spelling mistake in the control's filename, so it now matched the UserControl name, cleaned and re-built and Bobs your weird uncle's cat. :]

GO project property then 'Build' tab and check 'Target Platform' was 'AnyCPU'.