无法在表单上放置用户控件

Question

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?

Answer 1

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

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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:
  1. 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.
  2. 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

Answer 2

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...

Answer 3

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.

Answer 4

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.

Answer 5

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 (eg 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.

Answer 6

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).

Answer 7

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. :]

Answer 8

GO项目属性然后'Build'选项卡并检查'Target Platform'是'AnyCPU'。