Tracker Add-on Protocol

The Tracker provides a convenient shortcut mechanism through the use of add-ons. A user can access a special add-ons menu by right clicking in the Tracker. The Tracker interacts with an add-on through the process_refs() function described below.

Tracker add-ons should be placed in /boot/home/config/add-ons/Tracker. A shortcut key can be associated with the add-on by appending a dash followed by the shortcut key to the filename of the add-on.

process_refs()

Declared in: <be/add-ons/tracker/TrackerAddOn.h>

      void process_refs(entry_ref dir_ref, BMessage *msg, void *reserved)

The Tracker calls this function when the user invokes the add-on. The current directory is found in dir_ref. msg is a standard B_REFS_RECEIVED BMessage with the "refs" array containing the entry_refs of the files selected by the user. The third argument is currently unused.

process_refs() runs in a separate thread within the Tracker's team, so if your add-on crashes, the Tracker goes too. The Tracker unloads your add-on as soon as it returns from process_refs(). This can adversely affect your add-on if the code it is executing suddenly disappears. The solution is to wait until all the threads in your add-on terminate before returning from process_refs(). For example, in a simple add-on that spawns a single output window, you'd use something along the lines of:

   long dummy;
   wait_for_thread(window->Thread(), &dummy);

A simple Tracker Add-On follows. It simply takes the contents of the arguments to process_refs() and outputs them in a window.

   #include <Application.h>
   #include <InterfaceKit.h>
   #include <StorageKit.h>
   
   #include <stdio.h>
   #include <string.h>
   
   #include <be/add-ons/tracker/TrackerAddon.h>
   
   void process_refs(entry_ref dir_ref, BMessage *msg, void *)
   {
      BWindow *window = new BWindow(BRect(100,100,300,300),
         "Sample Tracker Add-on", B_TITLED_WINDOW, 0);
      BTextView *view = new BTextView(BRect(0,0,200,200), "view",
         BRect(0,0,200,200), B_FOLLOW_ALL_SIDES, B_WILL_DRAW | 
         B_FULL_UPDATE_ON_RESIZE);
      
      BPath path;
      BEntry entry(&dir_ref);
      entry.GetPath(&path);
      view->Insert("Current Directory: ");
      view->Insert(path.Path());
      view->Insert("\\n");
      
      int refs;
      entry_ref file_ref;
      for (refs=0;msg->FindRef("refs", refs, &file_ref) == B_NO_ERROR;refs++) {
      if (refs == 0)
            view->Insert("Selected files:\\n");
      entry.SetTo(&file_ref);
      entry.GetPath(&path);
      view->Insert(path.Path());
      view->Insert("\\n");
      }
      
      if (refs == 0)
      view->Insert("No files selected.\\n");
      
      view->MakeEditable(false);
      window->AddChild(view);
      window->Show();
   
      long dummy;
      wait_for_thread(window->Thread(), &dummy);
   }
   
   main()
   {
      new BApplication("application/x-sample-tracker-add-on");
      (new BAlert("", "Sample Tracker Add-on", "swell"))->Go();
      delete be_app;
   }

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Last modified January 21, 1998.