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I've been building DLL class libraries in C#, used as add-ons to an application which provides a Custom API. Up until now they've included mostly interfacing with databases, calculations, disk operations and so forth. I'm curious to know if I can build and display a Windows Form, displaying text boxes, buttons and so forth, inside a DLL Class Library?

I tried:

using System.Windows.Forms;

But that namespace is not recognized.

Thanks for the input.

default locale
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Cody Zink
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  • I just right clicked on class library > Add > New Item > Window Form with no problem. Am I missing something? – Neil Smith Jul 10 '14 at 23:44
  • In addidtion to the uses clauses also compare the references to those of a forms project! – TaW Jul 11 '14 at 06:55

6 Answers6

12

What I find works best for me is to create a new Windows Forms project, and then go to the project properties and change it to a class library. This way, you can right click on folders in the solution explorer and all the WinForms items appear just as if it were still a WinForms project, but it's a class library. This also works with WPF applications.

user2920518
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10

You can definitely use Windows Forms inside your class library. There are few scenarios:

  1. You are adding a form to the library using FormDesigner. You can right click on project name, click on Add and then in Windows form. It should add required References for your form

  2. You are copying a form from other project. In this case the Visual Studio will not be able to identify the form and will show it as simple C# source file. In this case right click on References under the project in Visual Studio. Click on Add References and select Framework from left pane. Select System.Windows.Form and System.Drawing and click Ok. This should make the form understandable to Visual Studio and you can design it edit it using Form Designer.

  3. If you are creating form using code, add the references to required assemblies as mentioned in the step 2. You should be able to use System.Windows.Form in your project with using System.Windows.Form; statement.
skjoshi
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5

Yes, you can. You need to add a reference to System.Windows.Forms in the class library project (right-click on project -> Add -> Reference)

AJ Richardson
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4

You can manually edit the project file to include windows forms:

Right click the project file --> "Edit Project File" and then under the <PropertyGroup> tag, add "<UseWindowsForms>true</UseWindowsForms>"

<PropertyGroup>
    <TargetFramework>net472</TargetFramework>
    <UseWindowsForms>true</UseWindowsForms>
    <OutputType>Library</OutputType>    
</PropertyGroup>
Blake
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0

It's 2021-7-29 and I'm using VS2019 and net5.

When creating a new project, there is a template named "Windows Form Class Library", with App.WindowsForm in it's dependencies as default.

God and Microsofters heard our pray.

cheny
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-1

if the New form is already in a Windows project that has to stay windows application..

try these Steps not sure if this is what you want... hope it helps.

  1. Create new Dll Project
  2. Copy Form.cs, FormDesigner.cs and form.resx into the new dll project Folder
  3. Add Existing
Code Assassin
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    This is 'a' solution but it is not convenient. Instead, I would create a Windows Forms Application project and change the output type to class library. That would help with adding required references and using them. – Cengiz Araz Nov 30 '16 at 06:49