You Do want a ShellExtension
What you want is not quite as simple as you think. The normal behavior for multiple file selections is to open each in a new Window/App instance. Actually, it just sends the selected files to the registered app and leaves it up to the app to decide how to work with them.
There is at least 1 quick and easy alternative though:
Method 1: Use Send-To
Open the Send To folder ("C:UsersYOURNAMEAppDataRoamingMicrosoftWindowsSendTo") and add an entry for the app. The target would be the app you wish to feed/send file selection to:
"C:Program FilesThat Other AppOtherApp.exe "
You don't need "%1" placeholders or anything else. You don't have to write an intermediary to do anything, just send the files directly to the actual app. It will work fine, as long as the app will accept more than one file on the command line.
The only minor thing is that it resides on a "shared" or general sub menu rather than a top level context menu. It is also not "smart" in so far as it is available for any file extension unlike a proper ContextMenu handler, but it is a quick and easy, no-code solution which has been around for a long time.
Method 2: Change the Verb Qualifier
You can also change the verb qualifier/mode, which sounds like the easiest way. Take for instance, VideoLan's VLC player:
If you click on multiple .MP4 files rather than open multiple instances, it opens with one of them and the rest are queued for play. This is done by modifying the verb in the registry:
+ VLC.MP4
+ shell
+ Open
- MultiSelectModel = Player
+ Command
- (Default) "C:Program Files.... %1"
MultiSelectModel is a modifier for the Open verb:
- Single for verbs that support only a single item
- Player for verbs that support any number of items
- Document for verbs which create a top level window for each item
For my MediaProps applet, since it is concerned with the same file types, I piggybacked my verb onto the file types of VLC by adding a ViewProps verb which was set as MultiSelectModel.Player and generally worked in so far as my verbs did not confuse VLC.
Unfortunately, there is still something amiss that I have not yet identified. Windows seems like it still is not gluing all the files together as expected - even if I make my own verbs. There is a step missing either in the registry config or with the app -- but with two other ways to do the same thing, I have never investigated further.
Method 3: Create ShellExtension / ContextMenu Handler
Many proposed solutions end up being a game of Whack-a-Mole where you have to fix the same 1 file-1 instance problem in an intervening app so it can feed concatenated arguments to the final actor. Since the end result is to have an Explorer ContextMenu to do something useful, lets just build a ShellExtension for this other application.
This is easy because a framework is already done and available on CodeProject: How to Write Windows Shell Extension with .NET Languages. This is an MS-PL article complete with a finished ShellExtension project.
With a few modifications, this will work perfectly to:
- setup associations for multiple file types
- collect multiple files clicked
- format them into a command line arg set
- pass the commandline to the actual worker app
- provide a custom ContentMenu
- display a snazzy menu icon
The test bed for this is an applet to display the MediaInfo properties of media files (things like Duration, Frame Size, Codec, format etc). In addition to accepting Dropped files, it uses a ContextMenu DLL helper to accept multiple files selected in Explorer and feed them to the Single Instance display app.
Very Important Note
Since this was first posted, I have revised and updated the original MS-PL article making it much easier to use. The revision is also at CodeProject Explorer Shell Extensions in .NET (Revised) and still contains a VB and C# version.
In the revised version, rather than having to make changes here and there, they are consolidated to a single block of variables. The article also explains why you might want to use the C# version, and provides links to articles explaining why it is not a good idea to use managed code for Shell Extensions.
The 'model' remains that of a Shell Extension to simply launch a related app.
The balance of this answer is still worth reading for the general concepts and background. It doesn't seem right to change it well after the fact even though much of the Code Changes section doesn't apply to the revision.
1. Update the Assembly/Project Values
For instance, I changed the assembly name to "MediaPropsShell". I also removed the root namespace but that is optional.
Add a PNG icon of your choosing.
Pick the appropriate platform. Since the original has 2 installers, you may have to specifically build an x86 version for a 32bit OS. AnyCPU works fine for 64bit OS, I'm not sure about x86. Most systems which use this model supply a 32 and 64 bit DLL for the shell extension helper, but most in the past could not be NET based either where AnyCPU is an option.
Keep the target platform as NET 4. If you did not read the CodeProject article or have not researched this previously, this is important.
2. Code changes
As published on CodeProject, the handler also only passes one file and associates itself with only one file type. The code below implements the handler for multiple file types. You will also want to fix the menu names and so forth. All the changes are noted in the code below prefaces with {PL}:
' {PL} - change the GUID to one you create!
<ClassInterface(ClassInterfaceType.None),
Guid("1E25BCD5-F299-496A-911D-51FB901F7F40"), ComVisible(True)>
Public Class MediaPropsContextMenuExt ' {PL} - change the name
Implements IShellExtInit, IContextMenu
' {PL} The nameS of the selected file
Private selectedFiles As List(Of String)
' {PL} The names and text used in the menu
Private menuText As String = "&View MediaProps"
Private menuBmp As IntPtr = IntPtr.Zero
Private verb As String = "viewprops"
Private verbCanonicalName As String = "ViewMediaProps"
Private verbHelpText As String = "View Media Properties"
Private IDM_DISPLAY As UInteger = 0
Public Sub New()
' {PL} - no NREs, please
selectedFiles = New List(Of String)
' Load the bitmap for the menu item.
Dim bmp As Bitmap = My.Resources.View ' {PL} update menu image
' {PL} - not needed if you use a PNG with transparency (recommended):
'bmp.MakeTransparent(bmp.GetPixel(0, 0))
Me.menuBmp = bmp.GetHbitmap()
End Sub
Protected Overrides Sub Finalize()
If (menuBmp <> IntPtr.Zero) Then
NativeMethods.DeleteObject(menuBmp)
menuBmp = IntPtr.Zero
End If
End Sub
' {PL} dont change the name (see note)
Private Sub OnVerbDisplayFileName(ByVal hWnd As IntPtr)
'' {PL} the command line, args and a literal for formatting
'Dim cmd As String = "C:Projects .NETMedia PropsMediaProps.exe"
'Dim args As String = ""
'Dim quote As String = """"
'' {PL} concat args
For n As Integer = 0 To selectedFiles.Count - 1
args &= String.Format(" {0}{1}{0} ", quote, selectedFiles(n))
Next
' Debug command line visualizer
MessageBox.Show("Cmd to execute: " & Environment.NewLine & "[" & cmd & "]", "ShellExtContextMenuHandler")
'' {PL} start the app with the cmd line we made
'If selectedFiles.Count > 0 Then
' Process.Start(cmd, args)
'End If
End Sub
#Region "Shell Extension Registration"
' {PL} list of media files to show this menu on (short version)
Private Shared exts As String() = {".avi", ".wmv", ".mp4", ".mpg", ".mp3"}
<ComRegisterFunction()>
Public Shared Sub Register(ByVal t As Type)
' {PL} use a loop to create the associations
For Each s As String In exts
Try
ShellExtReg.RegisterShellExtContextMenuHandler(t.GUID, s,
"MediaPropsShell.MediaPropsContextMenuExt Class")
Catch ex As Exception
Console.WriteLine(ex.Message)
Throw ' Re-throw the exception
End Try
Next
End Sub
<ComUnregisterFunction()>
Public Shared Sub Unregister(ByVal t As Type)
' {PL} use a loop to UNassociate
For Each s As String In exts
Try
ShellExtReg.UnregisterShellExtContextMenuHandler(t.GUID, s)
Catch ex As Exception
Console.WriteLine(ex.Message) ' Log the error
Throw ' Re-throw the exception
End Try
Next
End Sub
#End Region
Just below a bit needs to be changed in the IShellExtInit Members REGION as well:
Public Sub Initialize(pidlFolder As IntPtr, pDataObj As IntPtr,
hKeyProgID As IntPtr) Implements IShellExtInit.Initialize
If (pDataObj = IntPtr.Zero) Then
Throw New ArgumentException
End If
Dim fe As New FORMATETC
With fe
.cfFormat = CLIPFORMAT.CF_HDROP
.ptd = IntPtr.Zero
.dwAspect = DVASPECT.DVASPECT_CONTENT
.lindex = -1
.tymed = TYMED.TYMED_HGLOBAL
End With
Dim stm As New STGMEDIUM
' The pDataObj pointer contains the objects being acted upon. In this
' example, we get an HDROP handle for enumerating the selected files
' and folders.
Dim dataObject As System.Runtime.InteropServices.ComTypes.IDataObject = Marshal.GetObjectForIUnknown(pDataObj)
dataObject.GetData(fe, stm)
Try
' Get an HDROP handle.
Dim hDrop As IntPtr = stm.unionmember
If (hDrop = IntPtr.Zero) Then
Throw New ArgumentException
End If
' Determine how many files are involved in this operation.
Dim nFiles As UInteger = NativeMethods.DragQueryFile(hDrop,
UInt32.MaxValue, Nothing, 0)
' ********************
' {PL} - change how files are collected
Dim fileName As New StringBuilder(260)
If (nFiles > 0) Then
For n As Long = 0 To nFiles - 1
If (0 = Native
