windows-terminal/doc/creating_a_new_project.md

Creating a New Project

Creating a new WinRT Component DLL and referencing it in another project

When creating a new DLL, it was really helpful to reference an existing DLL's .vcxproj like TerminalControl.vcxproj. While you should mostly try to copy what the existing .vcxproj has, here's a handful of things to double check for as you go along.

• Make sure to <Import> our pre props at the top of the vcxproj, and our post props at the bottom of the vcxproj.

<!-- pre props --> 
<Import Project="..\..\..\common.openconsole.props" Condition="'$(OpenConsoleDir)'==''" />
<Import Project="$(OpenConsoleDir)src\cppwinrt.build.pre.props" />

<!-- everything else -->

<!-- post props -->
<Import Project="$(OpenConsoleDir)src\cppwinrt.build.post.props" />

• Add a <ProjectReference> to your new .vcxproj in both WindowsTerminal.vcxproj and TerminalApp.vcxproj
• Add a <Reference> to TerminalAppLib.vcxproj similar to this:

    <Reference Include="Microsoft.Terminal.NewDLL">
      <HintPath>$(OpenConsoleCommonOutDir)\TerminalNewDLL\Microsoft.Terminal.NewDLL.winmd</HintPath>
      <IsWinMDFile>true</IsWinMDFile>
      <Private>false</Private>
      <CopyLocalSatelliteAssemblies>false</CopyLocalSatelliteAssemblies>
    </Reference>

• Make sure the project has a .def file with the following lines. The WINRT_GetActivationFactory part is important to expose the new DLL's activation factory so that other projects can successfully call the DLL's GetActivationFactory to get the DLL's classes.

EXPORTS
DllCanUnloadNow = WINRT_CanUnloadNow                    PRIVATE
DllGetActivationFactory = WINRT_GetActivationFactory    PRIVATE

• For a bit more context on this whole process, the AppXManifest.xml file defines which classes belong to which DLLs. If your project wants class X.Y.Z, it can look it up in the manifest's definitions and see that it came from X.Y.dll. Then it'll load up the DLL, and call a particular function called GetActivationFactory(L"X.Y.Z") to get the class it wants. So, the definitions in AppXManifest are required for this activation to work properly, and I found myself double checking the file to see that the definitions I expect are there.
• Note: If your new library eventually rolls up as a reference to our Centennial Packaging project CascadiaPackage, you don't have to worry about manually adding your definitions to the AppXManifest.xml because the Centennial Packaging project automatically enumerates the reference tree of WinMDs and stitches that information into the AppXManifest.xml. However, if your new project does not ultimately roll up to a packaging project that will automatically put the references into AppXManifest, you will have to add them in manually.

Troubleshooting

• If you hit an error that looks like this:

  X found processing metadata file ..\blah1\Microsoft.UI.Xaml.winmd, type already exists in file ..\blah\NewDLLProject\Microsoft.UI.Xaml.winmd.
  

  The Microsoft.UI.Xaml.winmd is showing up in the output folder when it shouldn't. Try adding this block at the top of your .vcxproj

  <ItemDefinitionGroup>
  <Reference>
      <Private>false</Private>
  </Reference>
  </ItemDefinitionGroup>
  

  This will make all references non-private, meaning "don't copy it into my folder" by default.

• If you hit a Class not Registered error, this might be because a class isn't getting registered in the app manifest. You can go check src/cascadia/CascadiaPackage/bin/x64/Debug/AppX/AppXManifest.xml to see if there exist entries to the classes of your newly created DLL. If the references aren't there, double check that you've added <ProjectReference> blocks to both WindowsTerminal.vcxproj and TerminalApp.vcxproj.

• If you hit an extremely vague error along the lines of Error in the DLL, and right before that line you notice that your new DLL is loaded and unloaded right after each other, double check that your new DLL's definitions show up in the AppXManifest.xml file. If your new DLL is included as a reference to a project that rolls up to CascadiaPackage, double check that you've created a .def file for the project. Otherwise if your new project does not roll up to a package that populates the AppXManifest references for you, you'll have to add those references yourself.