Is there a way to automatically include content files into asp.net project file?

You simply can extend your website .csproj file. Just add your content root folder with a recursive wildcard:

...
<ItemGroup>
    <!-- your normal project content -->
    <Content Include="Default.aspx" />

    <!-- your static content you like to publish -->
    <Content Include="Images\**\*.*" />
</ItemGroup>
...

Doing so makes this folder and all content below visible inside your solution browser.

If you try to hide the folder inside the solution browser by specifying

<Content Include="Images\**.*.*">
    <Visible>false</Visible>
</Content>

it will not be published.

Update

As you already discovered the wildcard will be replaced as soon as you touch the folder inside your solution because VS projects are not designed to contain arbitrary content.

So you will have to make sure the folder and its contents are never modified from within VS - adding or removing files can only be done on the file system ... which is what you wanted as i understood your question.

It would be easier if the folder could be hidden in VS but i couldn't find a way to hide it AND publish.

Another unsuccessful approach was to include the folder by a CreateItem Task. This resulted in the contents of folder being published to \bin\app.publish\... and could not be convinced to publish it together with the content items inside the .csproj so i did not present it in my answer.

For those having issues using Chris' answer, this is the solution for Visual Studio 2012 and newer:

<Target Name="ContentsBeforeBuild" AfterTargets="BeforeBuild">
  <ItemGroup>
    <Content Include="images\**" />
  </ItemGroup>
</Target>

As Chris mentioned in his answer - Visual Studio will not touch this <Target> section, even if you manually fiddle around (adding/removing files) with the target directory.

Please note that you should include a subdirectory where the files are located (in the case above, it's images). Visual Studio/MSBuild will place those files in the same directory within the project structure. If you don't use a subdirectory, the files will be placed at the root of the project structure.

For a quick explanation of the wildcards:

• ** means everything recursively (files, subdirectories, and files within those)
• *.ext will include all files with extension ext within the top-level directory, but not subdirectories
  • For example, *.ext could be *.png, *.js, etc. Any file extension will work
• **\*.ext will include all files with extension ext from the top-level directory and all subdirectories.
• See the answer from How do I use Nant/Ant naming patterns? for a more complete explanation with examples.

For completion, please note that there is a difference between using <Target> and not using it.

With the <Target> approach, Visual Studio will not show the files within the Solution Explorer.

<Target Name="ContentsBeforeBuild" AfterTargets="BeforeBuild">
  <ItemGroup>
    <Content Include="images\**" />
  </ItemGroup>
</Target>

The non-<Target> approach will instruct Visual Studio to show the files within the Solution Explorer. The drawback with this one is that any manipulation of the automatic directories will cause Visual Studio to override the wildcard entry. It should also be noted that the approach below will only update the Solution Explorer upon opening the Solution/Project in VS. Even the Solution Explorer's "refresh" toolbar button won't do it.

<ItemGroup>
  <Content Include="images\**" />
</ItemGroup>

You can use the framework's System.IO.Directory.GetFile(string) method and its overloads to recursively include all files.

  <ItemGroup>
    <Content Include="$([System.IO.Directory]::GetFiles('$(ProjectDir)Scripts\', '*.js', SearchOption.AllDirectories))" />
    <Content Include="$([System.IO.Directory]::GetFiles('$(ProjectDir)Images\', '*.png', SearchOption.AllDirectories))" />
  </ItemGroup>

You can add folder with files recursively like this:

  <ItemGroup>
    <Content Include="somefolder\*.txt">
        <Link>%(RecursiveDir)myown_somefolder\%(Filename)%(Extension)</Link>
    </Content>
  </ItemGroup>

You can add files with links like this, they are searchable, view-able, but they do not checkout if you try to change them, also visual studio leaves the wildcards in place:

  <ItemGroup>
    <Content Include="..\Database Schema\Views\*.sql">
      <Link>Views\*.sql</Link>
    </Content>
  </ItemGroup>

This goes inside the .proj file.

I've written up how I was able to get the content includes created with a small powershell script:

$folders = Get-ChildItem .\ -r -Directory
$filtered = $folders |Select-Object @{Name='FullName';Expression={$_.fullname.replace($pwd,'')}}, @{Name='FolderDepth';Expression={($_.fullname.Split('\').Count) - ($Pwd.Path.split('\').count)}} | Sort-Object -Descending FullName,folderDepth 
$basefolders = $filtered | Where-Object{$_.folderdepth -eq 1}
$basefoldersobj = @()
foreach($basefolder in $basefolders)
{
  $basefoldername =$baseFolder.fullname
  $filteredbase = $filtered -match "\$basefoldername\\" | Sort-Object -Descending FolderDepth | Select-Object -first 1
  if($filteredbase -eq $null)
  {
    $filteredbase = $filtered -match "\$basefoldername" | Sort-Object -Descending FolderDepth | Select-Object -first 1
  }
  $obj = New-Object psobject
  Add-Member -InputObject $obj -MemberType NoteProperty -Name 'Folder' -Value $basefolder.fullname.trim('\')
  Add-member -InputObject $obj -MemberType NoteProperty -Name 'DeepestPath' -Value $filteredbase.folderDepth
  $basefoldersobj += $obj
}
$include = '*.*'
foreach($bfolderObj in $basefoldersobj)
{
  $includecount = ''
  $includecount = "\$include" * ($bfolderObj.Deepestpath)
  Write-Output "<content Include=`"$($bfolderObj.folder)$includecount`" /> "
}

This should produce the necessary include statement at the powershell prompt

Not to my knowledge; however my suggestion is to paste them into the project as this will include them by default. So, instead of pasting them into the directory via Explorer, use Visual Studio to paste the files into the folders.