Joaquim Rocha
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Long press GTK+ TreeView on Maemo

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    Joaquim Rocha
  • Principal Software Engineering Manager at Microsoft

Yesterday was a holiday so I got some time to hack a bit in SeriesFinale. One of the things I wanted to do was to have a context menu for shows and seasons. Something to apply individual actions like deleting, updating, viewing information, etc when there is a long press on a tree view’s item.

In Maemo the way to do this is to use the TreeView’s tap_and_hold_setup method but the problem is that I hate how this context menu is implemented: I have accidentally deleted stuff because of this menu. Can you think of a less intuitive widget for a touch screen? One that shows below your thumbs, only while you’re touching the screen and triggers some action when you lift it. Instead, I wanted to show a dialog with the different actions so users could easily know what their doing. Also, the fact that the API only allows me to use this long-press action to trigger a menu widget doesn’t seem like the best design…

Because of this I decided to implement a TreeView’s subclass that makes it better! In my opinion, the way to implement this in the TreeView is to treat it like any other functionality: emit a signal when it occurs.

Though it wasn’t difficult, I thought the job would be easier. I had already implemented the “long-press” signal emission but the “row-activated” signal kept being emitted as well. Contrary to what I thought, re-implementing do_row_activated didn’t do it so I had to take a look at the GTK+’s source and though the row_activated method is indeed the one that emits the signal, there is also a “hildon-row-tapped” signal being emitted from the button_release_event. I don’t know if this signal is related or if it is the Python bindings fault but I had to prevent the “row-activated” signal from the mouse_released_event method in a hackish way

Finally, when running the dialog, the application would freeze and not respond after this. It was related to the emission being done from the timeout callback which, without having the time to look further, smelled like some race condition so I had to wrap the signal emission with the threads_enter/leave. After this, everything worked well.

Like the “row-activated”, the “long-press” signal gives the tree path and the column that was pressed. It is emitted after pressing for 0.5 seconds and is cancelled if meanwhile the user moves the finger more than 25 pixels. These values are completely arbitrary and have just worked good enough for me. Of course you can easily change them.

And that’s it. I’ve called it EnhancedTreeView and if you want to use it in your Maemo application go ahead and copy/tweak the file (it has less than 60 lines).