Visual Studio C++/CLI Error : “Failed to load toolbox item, It will be removed from Toolbox”

Question

Visual Studio C++/CLI Error : “Failed to load toolbox item, It will be removed from Toolbox”

Wami007 296

Picture Linked to Title, I was try to:

Clean and Rebuild won't work
Project built in x86
Restart V.S doesn't work I just:
Created Form and userControl by Default name
Linked To Windows and Advanced to "main"
Added code in Form.cpp to fix Designer error and restart V.S
Try to Drag userControl but no luck ;(

Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2021-04-08T02:56:07.947+00:00
@Wami007

I suggest you could try to create an instance of user control.

Suppose you have myusercontrol.cpp with same namespace in your project.
Add this code in you form where you want to use myusercontrol.

MyUserControl ob = gcnew MyUserControl(); this->Controls->Add(ob);
Wami007 296 Reputation points

2021-04-08T20:35:14.417+00:00

Sir, If you want try it on your V.S but when i add this code to my MainForm, designer return error to me....
Wami007 296 Reputation points

2021-04-08T20:35:53.03+00:00

Sir, If you want try it on your V.S but when i add this code to my MainForm, designer return error to me....
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2021-04-09T06:54:58.387+00:00

@Wami007

Could you please provide some steps and a code sample that help us reproduce the issue?

For more details about how to create a c++/cli User Control, I suggest you could refer to the link: https://stackoverflow.com/questions/61423056/creating-a-clr-user-control
Viorel 125.8K Reputation points

2021-04-09T10:26:13.877+00:00

Maybe the User Control includes some code that cannot be executed on design stage, giving an exception. The DesignMode property can be used to exclude inappropriate code. Show some details about your user control and try to replicate the problem with a new User Control that does not include additional code.
Wami007 296 Reputation points

2021-04-09T13:10:08.527+00:00

All codes is default after creating form and control i don't add any code but give error
Wami007 296 Reputation points

2021-04-10T21:29:23.96+00:00

I created ClassLibrary project, added UserControl to Form succesfully but in this case Startup item is .dll i can't change Startup item to mainForm.
When i try build ClassLibrary it Say " .dll isn't valid win32 application "

Your answer

Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2021-04-08T02:56:07.947+00:00

@Wami007

I suggest you could try to create an instance of user control.

Suppose you have myusercontrol.cpp with same namespace in your project.
Add this code in you form where you want to use myusercontrol.

MyUserControl ob = gcnew MyUserControl(); this->Controls->Add(ob);
Wami007 296 Reputation points

2021-04-08T20:35:14.417+00:00

Sir, If you want try it on your V.S but when i add this code to my MainForm, designer return error to me....
Wami007 296 Reputation points

2021-04-08T20:35:53.03+00:00

Sir, If you want try it on your V.S but when i add this code to my MainForm, designer return error to me....
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2021-04-09T06:54:58.387+00:00

@Wami007

Could you please provide some steps and a code sample that help us reproduce the issue?

For more details about how to create a c++/cli User Control, I suggest you could refer to the link: https://stackoverflow.com/questions/61423056/creating-a-clr-user-control
Viorel 125.8K Reputation points

2021-04-09T10:26:13.877+00:00

Maybe the User Control includes some code that cannot be executed on design stage, giving an exception. The DesignMode property can be used to exclude inappropriate code. Show some details about your user control and try to replicate the problem with a new User Control that does not include additional code.
Wami007 296 Reputation points

2021-04-09T13:10:08.527+00:00

All codes is default after creating form and control i don't add any code but give error
Wami007 296 Reputation points

2021-04-10T21:29:23.96+00:00

I created ClassLibrary project, added UserControl to Form succesfully but in this case Startup item is .dll i can't change Startup item to mainForm.
When i try build ClassLibrary it Say " .dll isn't valid win32 application "

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Visual Studio C++/CLI Error : “Failed to load toolbox item, It will be removed from Toolbox”

Your answer