Associating a file type to my program?

lansing

I have a multi tab text editor program and I want to associate a file type to it, so when we double click on the file, my program will open it in a new tab.

From my understanding, I'll need to first register the file type and shell command in registry to:

HKEY_CURRENT_USER\SOFTWARE\Classes\.myextension
HKEY_CURRENT_USER\SOFTWARE\Classes\.myextension\Shell\Open\Command = "C:\my_program.exe" "%1".

And then I can retrieve the file path in main(int argc, char *argv[]) in my c++ file with argv[0].

But how do I keep my program at only one instance? Right now if I double click the file type, it will open a new instance of my program.

jsulm

@lansing said in Associating a file type to my program?:

But how do I keep my program at only one instance?

See this thread: https://forum.qt.io/topic/98417/how-to-create-singleinstance-application/13

lansing

@jsulm

Is there another alternative with less hassle? That's a lot of files to add for this feature.

jsulm

@lansing I don't know about any simpler solution

raven-worx

@lansing
clone into your project source [https://github.com/KDAB/KDSingleApplication] and include the .pri file in your .pro file

lansing

I have implemented the SingleApplication from here, and now double clicking on the text file will not open a second instance of the program. But it wouldn't open my file in a new tab.

JonB

@lansing
Glancing through that link, you will have to implement what is in the Secondary Instances sub-section. Have you done so?

Here is an example of how you would start a Secondary Instance send a message with the command line arguments to the primary instance and then shut down.

That is what you want, isn't it?

lansing

@JonB

Yes, so I got the secondary instance sending message to the first instance now. But it was sending a joined QByteArray and I don't know how to split it back in the slot.

    if( app.isSecondary() ) {
        app.sendMessage( app.arguments().join(' ').toUtf8() );        
        return 0;
    } else {
        QObject::connect(
            &app,
            &SingleApplication::receivedMessage,
            mainwindow,
            MainWindow::slotReceivedMessage
        );
    }

The QByteArray I received is "my_program.exe D:\myfile.txt", how do I get the myfile.txt string?

SGaist

Hi,

You can split your string however why to just send the relevant arguments rather than just all of them ?

JonB

@lansing
Well QString::split() will be the simplest to handle "my_program.exe D:\myfile.txt". Though you might want to test with a space in the filename passed in, that might be more tricky, don't know if you can use the QString::split(const QRegularExpression &re) overload for that.

lansing

@SGaist said in Associating a file type to my program?:

Hi,

You can split your string however why to just send the relevant arguments rather than just all of them ?

Oh yes you're right, I can just send app.sendMessage( argv[1] ) . A new problem I see is that my file path that was sent will get shrink if it's too long. Like this
C:\Users\Me\Desktop\MYFILE~1.TXT. Is this normal?

JonB

@lansing
That's just a short (8.3) filename. Nothing you can do about it if that's what you receive. Should work.

lansing

@JonB

How do I get the original name back? I tried QFileInfo(filePath).absoluteFilePath() but it still couldn't convert it.

JonB

@lansing
I believe this will need a Windows-specific function call, and will not be available as a native Qt call. See GetLongPathNameA function (fileapi.h).

lansing

@JonB

I've been trying for 2 days but I couldn't get it to work:

main.cpp

int main(int argc, char *argv[])
{    
    SingleApplication application( argc, argv, true);
    mainWindow = new MainWindow();

    if (application.isSecondary()) {
        if (application.arguments().count() == 2) {
            application.sendMessage( argv[1] );
        }
        return 0;
    } else { 
        QObject::connect(&application, &SingleApplication::receivedMessage,
                    mainWindow , &MainWindow::slotReceivedMessage);
    }

mainwindow.cpp

namespace Win32 {
#include "Windows.h"
}

#define BUFSIZE 4096
void MainWindow::slotReceivedMessage(int instanceId, QByteArray message)
{
    Win32::DWORD  retval=0;
    Win32::BOOL   success;
    Win32::TCHAR  buffer[BUFSIZE];
    Win32::TCHAR  buf[BUFSIZE];
    Win32::TCHAR** lppPart={NULL};

    // convert char * to wchar_t *
    const size_t WCHARBUF = 100;
    wchar_t message_t[WCHARBUF];
    Win32::MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, message, -1, message_t, WCHARBUF);

    // get full filename from short filename
    retval = Win32::GetFullPathName(message_t, BUFSIZE, buffer, lppPart);
    QString filePath = QString::fromWCharArray(buffer);

    qDebug() << message;
    qDebug() << filePath;    
}

Since GetFullPathName needs a wchar_t as input, I have to first convert the char to wchar_t, then convert it to full path name.

But when printing out with debug, both the input(message) and output(filePath) are still the same. The GetFullPathName wasn't doing anything. What am I doing wrong?