How do I add my new User Control to the Toolbox or

问题:

I have an existing library (not a Winforms application) that supplies some Winforms to a bona-fide Windows application. Within this library, I would like to create a User Control to group some controls together. To accomplish this, I right-clicked, Add, User Control and dragged some controls onto the new User Control.

So far, so good. The User Control even has the requisite User Control icon. But dragging the new User Control from the Solution Explorer to a new blank Winform does not work (I get a circle with a line through it), and dragging it over to the Toolbox doesn't work either (even though I get a + sign when I drag it over the Toolbox).

Is there some sort of XML magic or something else I'm missing to make this work?

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Note: I had some problems with Visual Studio 2008 that I managed to fix by following the workarounds that can be found here. I am now able to get User Controls I added to my existing project into the toolbox by simply rebuilding the project.

回答1:

Assuming I understand what you mean:

1. If your UserControl is in a library you can add this to you Toolbox using

   Toolbox -> right click -> Choose Items -> Browse

   Select your assembly with the UserControl.

2. If the UserControl is part of your project you only need to build the entire solution. After that, your UserControl should appear in the toolbox.

In general, it is not possible to add a Control from Solution Explorer, only from the Toolbox.

回答2:

One way to get this error is trying to add a usercontrol to a form while the project is set to compile as x64. Visual Studio throws the unhelpful: "Failed to load toolbox item . It will be removed from the toolbox."

Workaround is to design with "Any CPU" and compile to x64 as necessary.

Reference: https://support.microsoft.com/en-us/kb/963017