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There is a contents page for all these posts.

Matters arising from last time. Several people have been replying to these posts as if I was the embodiment of the Maemo team. Although I worked on some really interesting parts of the desktop as part of a team from Collabora, I didn’t have anything to do with the package format or anything like that, and I’m writing these posts as an individual (and I welcome corrections). If you want to ask about the rationale behind anything here, there might be people who would know more at talk.maemo.org.

It’s a grand life on the buses. One of the many wonderful things to happen to the free desktop in recent years has been the invention of DBus as the glue to stick it all together; it’s gone a long way towards making Unix not suck.  Maemo sticks together with DBus just as much as GNOME or KDE do, which means we can interact with system services fairly painlessly.  And if we don’t know how to do something, we can always run dbus-monitor, use some other program to do what we wanted to do, and see how it managed.  Then we know what to google for when we’re looking for the official documentation.

Sharing is good. So today we’re going to be adding a “share” button to the app, so that we can tell our friends when we find an interesting link on reddit, and we’re going to be doing it using only a DBus client. Adding the entry to the menu is pretty trivial:

Now, let’s consider how we might want to share things with people:

• Microblogging (twitter, identi.ca…): yes, definitely. You can very simply post a message to an account on one of these systems using DBus services provided by a library called microfeed. We’ll add an optional dependency on that library, and assume that people who are using it will already have set it up (using Mauku or something similar).
• Email: certainly. We can interact with the email subsystem using DBus services provided by modest.
• IM: yes, but… We could do this by putting up a dialogue from the address book, waiting for them to choose a contact, and then sending the message using Telepathy. But that’s not what we want; what we want is to start a conversation: we want to put up the IM window with the link as a sent message and allow the recipient to respond. I don’t know a good way of doing that, but maybe you do.
• “Sharing services” usually means file hosting services like share.ovi.com, and isn’t really the sort of thing that concerns us here– even if the link’s to an image, you probably don’t want to upload a second copy of the image to your Ovi account.
• Bluetooth: probably overkill (do people really send URLs over bluetooth? Apparently they do, actually, so maybe we’ll add that later.)

But let’s stick with microblogging and email for now. I’ve created a rather rough version of this idea as a separate file, sharing.c, in case it could be separately useful to someone else. This brings us up to raeddit-06 (diff to raeddit-05, git cloneable, and available from maemo-extras). When the user taps “Share”, this part of the program will put up another selector listing “Email” and as many microblogging services as it can find:

Let’s say we choose Twitter; then the message gets posted, and we can go and check it in Mauku or the web browser:

Behold the power of DBus!

Next time we’ll be adding the ability to view images in-process rather than launching the web browser, and we’ll be learning about a rather wonderful innovation called “stackable windows”.

There is a contents page for all these posts.

Matters arising from last time: There’s been some very helpful feedback:

• Colin Watson pointed out that debhelper 7 makes building debian/rules files far, far simpler. But Jonny Lamb told us that Maemo doesn’t ship with debhelper 7.
• A Nokian emailed me to point out that in Maemo 5, application icons should be 48×48, and that 26×26 is from Maemo 4. (26×26 will still work, though, as we saw.)
• Several people pointed out that the “B” in “XB-Maemo-Icon-26” stands for “binary”.
• And someone on Reddit said that “raeddit” is not a particularly wonderful name. This is true, and I’m open to better suggestions. I didn’t want to call it “reddit” without asking the reddit admins!

Today we’re going to introduce another new widget which is specific to Maemo.  The program currently opens the target site when you click a link. Last time, we promised to make it put up a menu of possibilities, instead:

Selectors. This is called a HildonTouchSelector, and it pops up (so to speak) all over the place. It can live inside any window, but it also has its own special kind of dialogue called a HildonPickerDialog.  It’s very like a combo box, but much easier to use with your fingers.

You see that the program behind the selector is blurred out: that’s to show that it’s not available. If you were to tap the blurred area, the selector would close without making any choices, and you would return to the rest of the program. You can also see that the switcher button at top left is not blurred: that’s because the selector is only modal, not system-modal. You can’t interact further with this program until you deal with the selector, but you’re free to switch to another program or start a new one.

What do we actually need? Now, before we dive into coding, let’s think about what we need from any representation of one of the lines in the menus.

• We will need to ask it for the text to appear in the menu.
• And it should be able to decline to appear in the menu.  For example, “vote up” should only appear if you’re logged in.
• We will need to ask it to deploy, if it’s chosen.

How could we best implement that?

• The fairly elegant way would be a set of singleton classes all implementing a common interface.
• The very elegant way would be a set of DBus services.  That way, third parties could come along and add new menu options.
• And perhaps we’ll do it the very elegant way later.  But this is a quick and simple tutorial, so…

We’ll use a set of callbacks.

• Each callback takes a representation of the post, and a boolean– true if we’re preparing, false if we’re deploying– and returns a char*.
• If we’re preparing, the char* is the name that will appear in the menu, and should be freed by the caller.
• But if we’re preparing, the callback may also return NULL, to decline to appear in the menu.
• If we’re deploying, the callback should always return NULL.
• We promise not to ask a callback to deploy if it returned NULL in the preparation stage.

A small amount of extra work brings us to raeddit-05 (diff to raeddit-04, git cloneable, and available from maemo-extras).  This contains two callbacks: one to visit the actual site, and one to visit the comments page on reddit.  It looks like this:

It’s already much more useful this way, but it’s looking a bit bare with only two entries.  Clearly we can’t put in “vote up” or “vote down” until we allow the user to log in. We could easily put in the ability to buy a shirt, but there seem more important things to do first.

For example, every good mobile application needs a “share” button.  So next time we’ll be looking at how to add an entry which lets us IM or email the link to our friends, or post the link to twitter or identi.ca.