How to pass several files at once to my registered application?

Question

In a Delphi 10.4.2 win-32 VCL Application associated with graphic file formats in Windows 10, I get parameter files selected in Windows File Explorer. Here I watch the files passed to my app right after Application.Initialize;:

CodeSite.Send('AppInstances: ParamCount', ParamCount);

When I select ONE file in Explorer and then press the ENTER key, this file gets loaded in my application. So far so good.

But when I select THREE files in Explorer and then press the ENTER key, my app gets started THREE times each time with ONE of the 3 file parameters:

Is it possible that Explorer would start my app only ONCE and pass the 3 selected files at once to my app when I press the Enter key?

Answer 1

SUMMARY

1. In Registry put the target program as Context Menu Create File.exe which writes reg.txt file.

2. In your main program loop every 1 second to check if reg.txt exists. If it exists, kill the Context Menu Create File.exe and delete the reg.txt file. Then copy the selected file paths and manipulate with them.

3. If your program loops to check for reg.txt, then you need to start the program before executing context menu either on startup or manually.

I did this with AutoHotkey.

These 2 AutoHotkey scripts below allow you to add a Open With Chrome context menu item in Windows Explorer to open multiple selected files.

You can leave all variable values as they are, but if you want to change the contextMenu value and program name then see 3.1.

INSTRUCTIONS:

Create 2 files in the same directory:

1. Create 1st program Add To Context Menu And Create Startup Shortcut.ahk

   1. RunAsAdmin Label ensures that the script runs as admin (fixes adding Registry values).

      1. The If (!A_IsAdmin) checks if current user is NOT admin, A_IsAdmin is a built in AutoHotkey variable that returns 1 if user is admin, 0 otherwise.
      2. Run, \*RunAs "%A_ScriptFullPath%" *RunAs parameter runs the script as admin, "%A_ScriptFullPath%" gets the full path of the current executing script.
      3. ExitApp exits the current script instance running without admin privileges.
      4. Because the Run command runs the script again with admin privileges it will skip the IF condition and continue executing code below.

   2. ContextMenuCreateFile: Label creates a Context Menu Create File.exe which creates a file reg.txt and exits Context Menu Create File.exe after it has written the file reg.txt. Make sure you specify where your Ahk2Exe.exe path is in the RunWait command.

   3. Add To Context Menu: Label adds the Registry entry which runs Context Menu Create File.exe.

      1. Set the contextMenu variable to what needs to be displayed in the Context Menu. (The program name is set to contextMenu)
      2. Set the regPath to your desired Registry path.
      3. When it executes the MsgBox, check if the command is added to the Registry in the address bar.

   4. CreateStartupShortcut: Label creates the shortcut of the main program Open With Chrome.exe in Startup folder.

Add To Context Menu And Create Startup Shortcut.ahk

; =============Recommended Settings=============
#NoEnv
SetWorkingDir %A_ScriptDir%
#Warn
CoordMode, Mouse, Window
SendMode Input
#SingleInstance Force
SetTitleMatchMode 2
SetTitleMatchMode Fast
DetectHiddenWindows Off
DetectHiddenText On
#WinActivateForce
#NoTrayIcon
SetControlDelay 1
SetWinDelay 0
SetKeyDelay -1
SetMouseDelay -1
SetBatchLines -1
#Persistent
#MaxThreadsPerHotkey 2
; =============Recommended Settings=============

AddToContextMenuAndCreateStartupShortcut:
RunAsAdmin:  ; =============RunAsAdmin=============
If (!A_IsAdmin)  ; IF NOT Admin
{
    Run, *RunAs "%A_ScriptFullPath%"  ; Run script as admin
    ExitApp  ; Exit the current instance running without admin privileges
}
ContextMenuCreateFile:  ; =============ContextMenuCreateFile=============
contextMenuCreateFileAhk := 
(LTrim
"#NoEnv
#NoTrayIcon
#SingleInstance Force
SetWorkingDir %A_ScriptDir%
SetBatchLines -1

ContextMenuCreateFile:
FileDelete, reg.txt
FileAppend, , reg.txt
ExitApp
Return"
)  ; contextMenuCreateFileAhk
FileDelete, Context Menu Create File.exe  ; DEL Context Menu Create File.exe
FileDelete, Context Menu Create File.ahk  ; DEL Context Menu Create File.ahk
FileAppend, %contextMenuCreateFileAhk%, Context Menu Create File.ahk  ; MAKE Context Menu Create File.ahk
RunWait, C:\Program Files\AutoHotkey\Compiler\Ahk2Exe.exe /in "Context Menu Create File.ahk" /out "Context Menu Create File.exe"  ; Convert AHK to EXE
FileDelete, Context Menu Create File.ahk  ; DEL Context Menu Create File.ahk
AddToContextMenu:  ; =============AddToContextMenu=============
path := ""  ; path
program := "Context Menu Create File"  ; program
contextMenu := "Open With Chrome"  ; contextMenu
regPath := "HKCR\*\shell"  ; regPath
StringReplace, regKey, contextMenu, %A_Space%, , A  ; regKey
regKey := 0 regKey  ; regKey
Loop, Files, %program%.exe, F  ; Find Program.exe In Current Dir
{
    path := A_LoopFileLongPath  ; Set Program Path
}
cmd := 
(LTrim
"reg add """ regPath "\" regKey """ /ve /t REG_SZ /d """ contextMenu """ /f
reg add """ regPath "\" regKey "\command"" /ve /t REG_SZ /d ""\""" path "\""`"" /f"
)  ; Registry
FileDelete, Add To Context Menu.bat  ; CREATE Add To Context Menu.bat
FileAppend, %cmd%, Add To Context Menu.bat  ; CREATE Add To Context Menu.bat
RunWait, Add To Context Menu.bat, , Hide  ; RUN Add To Context Menu.bat (*RunAs ADMIN)
FileDelete, Add To Context Menu.bat  ; DEL Add To Context Menu.bat
Run, regedit  ; regedit
WinWait, Registry Editor ahk_class RegEdit_RegEdit ahk_exe regedit.exe  ; Registry
Sleep, 333
ControlSetText, Edit1, %regPath%\%regKey%\command, Registry Editor ahk_class RegEdit_RegEdit ahk_exe regedit.exe  ; regPath
ControlFocus, Edit1, Registry Editor ahk_class RegEdit_RegEdit ahk_exe regedit.exe  ; regPath
ControlSend, Edit1, {Enter}, Registry Editor ahk_class RegEdit_RegEdit ahk_exe regedit.exe  ; regPath
ControlSend, SysListView321, {Control Down}{NumpadAdd}{Control Up}, Registry Editor ahk_class RegEdit_RegEdit ahk_exe regedit.exe  ; regPath
ControlSend, SysListView321, {F5}, Registry Editor ahk_class RegEdit_RegEdit ahk_exe regedit.exe  ; regPath
MsgBox, 262192, CHECK, Check If Added %contextMenu% To Registry  ; CHECK
CreateStartupShortcut:  ; =============CreateStartupShortcut=============
path := ""  ; path
program := contextMenu  ; program
Loop, Files, %program%.exe, F  ; Find Program.exe In Current Dir
{
    path := A_LoopFileLongPath  ; Set Program Path
}
FileCreateShortcut, %path%, %A_Startup%\%program%.lnk  ; Create Startup Shortcut
Run, %A_Startup%, , Max  ; Check If Shortcut Created
Run, "%program%.exe"  ; Run Program
MsgBox, 262144, CHECK, Check If Shortcut Created  ; CHECK
ExitApp  ; ExitApp
Return

2. Create 2nd program Open With Chrome.ahk which is the main program.
   1. Here a Loop is created and checks every 1 second if reg.txt exists.
   2. IfExist, reg.txt it kills the Context Menu Create File.exe and deletes the reg.txt.
   3. Then it activates explorer.exe window and copies all selected file paths to CLIPBOARD.
   4. If CLIPBOARD contains .,\ to make sure CLIPBOARD contains path "\" with extension ".".
   5. The list of selected files is saved in selectedFiles variable.
   6. The Loop below chromeParams := "" loops through selected files, gets the filePaths and surrounds them with double quotes, and StringReplace replaces the Windows path as url file path ex: C:\path\file.jpg to file:///path/file.jpg.
   7. Then the filePath is concatenated to chromeParams.
   8. StringTrimRight removes the last space from chromeParams string.
   9. Then Run, chrome.exe %chromeParams% is executed with %chromeParams% (list of selected files). (If the command doesn't open Chrome then put full path to Chrome, ex: Run, C:\Program Files (x86)\Google\Chrome\Application\chrome.exe with the same parameters)

Open With Chrome.ahk

; =============Recommended Settings=============
#NoEnv
SetWorkingDir %A_ScriptDir%
#Warn
CoordMode, Mouse, Window
SendMode Input
#SingleInstance Force
SetTitleMatchMode 2
SetTitleMatchMode Fast
DetectHiddenWindows Off
DetectHiddenText On
#WinActivateForce
#NoTrayIcon
SetControlDelay 1
SetWinDelay 0
SetKeyDelay -1
SetMouseDelay -1
SetBatchLines -1
#Persistent
#MaxThreadsPerHotkey 2
; =============Recommended Settings=============

OpenWithChrome:
Loop  ; Loop Start
{
    Sleep, 1000  ; Fix High CPU
    IfExist, reg.txt  ; IF reg.txt EXIST
    {
        RunWait, cmd /c taskkill /im "Context Menu Create File.exe" /f, , Hide  ; Fix Opening 2 Compose Windows
        FileDelete, reg.txt  ; DEL reg.txt
        WinActivate, ahk_class CabinetWClass ahk_exe explorer.exe  ; Explorer
        CLIPBOARD := ""  ; Clear Clipboard
        Send, {Control Down}{c}{Control Up}  ; Copy File Paths
        ClipWait, 0  ; Clip Wait
        If CLIPBOARD contains .,\  ; IF CLIPBOARD contains .,\
        {
            selectedFiles := CLIPBOARD  ; selectedFiles
            chromeParams := ""  ; chromeParams
            Loop, Parse, selectedFiles, `n, `r  ; Loop Start selectedFiles
            {
                filePath := """file:///" A_LoopField """"  ; filePath
                StringReplace, filePath, filePath, \, /, A  ; Replace \ with /
                chromeParams .= filePath . " "  ; chromeParams .= %filePath%,
            }
            StringTrimRight, chromeParams, chromeParams, 1  ; Remove Last Space
            Run, chrome.exe %chromeParams%  ; Open Files In Chrome
        }
    }
}
Return

3. Convert both Add To Context Menu And Create Startup Shortcut.ahk and Open With Chrome.ahk to EXE files in the same directory using Ahk2Exe.exe --> (find in Start Menu, just browse file and hit convert)

4. Execute the Add To Context Menu And Create Startup Shortcut.exe

5. Select files, right click and the Open With Chrome context menu item should appear.

Answer 2

On Windows 7 and later ¹, you can register a MultiSelectModel value (either Document or Player) with your file association verb(s) in the Registry. This is the easiest way to allow Explorer to send multiple files at a time to a single instance of your app, such as in separate command-line parameters.

^{1: I don't know exactly when this feature was first introduced.}

Prior to MultiSelectModel, other ways to handle this included:

• implementing the IDropTarget interface in your app, and then registering the DropTarget with your file association verb(s). The Shell can then construct an IDataObject containing information about the files(s), and pass it to your IDropTarget implementation (also see this article). This is the preferred method, as it does not suffer from limitations that other methods have (including MultiSelectModel!), and it allows for more flexibility as the same IDropTarget implementation can accept multiple files executed in Explorer, files dropped onto your app's window, even dropped onto the app's .EXE file itself. It is just a matter of registering the same IDropTarget with the appropriate APIs.

• Implementing a DDE server in your app, and then registering the server with your file association verb(s). The Shell can then start a DDE conversation with your app and send the file paths over to it using your specified command(s).

• just accepting the Shell starting a separate process for each file. Before your app creates its UI, have its startup code check for a file path on its command-line, and if found then look for another instance of your app already running, and if found then use an Inter-Process Communication mechanism of your choosing (ie, WM_COPYDATA, named pipe, socket, mailslot, etc) to send the file path to that existing instance, and then exit.