Make app bundle open files from Finder

[rolandlo]

I'm struggling to get my (C++) Gtk 3 app (built around GtkApplication/GApplication and bundled via gtk-mac-bundler) to open documents via double click in MacOS Finder (or alternatively via open doc.myExt or open -a MyApp.app doc.myExt from the terminal). Any of those will raise an error message like

The document "doc.myExt" could not be opened. MyApp cannot open files in the "myExt Document" format.

and then launch myApp (via the activate signal handler of my GApplication).

My understanding is that Finder and the open command use Launch Services to identify the preferred app and to actually open a document in the preferred app (if not explicitely stated in the open command), and Launch Services sends an Apple Event to the app that should open the document. I assume that the GApplication receives that Apple Event and calls its "open" signal handler, passing the list of files to be opened.
For associating the app bundle with the file extension (say myExt) I use a block like

    <key>CFBundleDocumentTypes</key>
    <array>
      <dict>
        <key>CFBundleTypeExtensions</key>
        <array>
          <string>myExt</string>
        </array>
        <key>CFBundleTypeIconFile</key>
        <string>myIcon.icns</string>
        <key>CFBundleTypeName</key>
        <string>myExt Document</string>
        <key>CFBundleTypeMIMETypes</key>
        <array>
          <string>application/myExt</string>
        </array>
        <key>CFBundleTypeRole</key>
        <string>Editor</string>
      </dict>
    </array>

This appears to work in so far as the double click in Finder or the open doc.myExt opens myApp (and not a different app). Also when I use the --args option in the open command to pass the file name

open -a myApp.app --args doc.myExt

or simply run

myApp.app/Contents/MacOS/myApp doc.myExt

it works fine (and uses the open signal handler). So I'm really wondering what goes wrong here and if GApplication/Gtk3 really support this feature.

Any help would be appreciated. If I should provide a minimal example, let me know.

[jralls]

I don't have direct knowledge. I'm still using [gtk-mac-integration[(https://gitlab.gnome.org/GNOME/gtk-mac-integration), which does handle the open file notification. Grepping openFile: in gtk and glib turns up nothing so I suspect that GApplication doesn't catch the notification and convert it to a signal. You could lift the code from gtk-mac-integration and add it to your app. Note that there's a timing issue, the details of which I don't remember perfectly, in the open-by-double-clicking use case: IIRC the fileOpen: notification comes after you call [NSApp finishLaunching] and you probably want to process it before you call gtk_main().

[rolandlo]

Thanks for the help. Grepping openFile (without the :) in gtk I actually discovered
https://gitlab.gnome.org/GNOME/gtk/-/blame/gtk-3-24/gtk/gtkapplication-quartz.c#L98
and the PR that added this openFiles delegate https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/2098

The thing I was missing was to add the line

g_object_set (G_OBJECT (app), "register-session", TRUE, NULL);

It works now for my simple GApplication. If anyone is interested, here is a minimal working example that I set up:
https://github.com/rolandlo/mactest/

[jralls]

Cool. Thanks for digging in.