Moving to the next page in MafwGriloSource

Thank Aldon Hynes, who sent me an email with some comments about MafwGriloSource behavior in the N900, I could fix a bug and implement a feature. The bug was a limitation when browsing, as you could only see the first 64 results. It was caused by a problem with indexes when returning the results, as I alwayes sent 0. When fixing this, the interface was requesting more and adding them to the treeview. Then we had all results in the treeview.

Then the problem I saw was that loading so many items in treeview was not slow, but a never ending story, as it took a long time to stop because we were asking for more pages until we reached the end, which took a long time.

I thought of a way of providing my own pagination and the first step was reverting the fix for the index bug to avoid the interface requesting more pages itself, which is a bit hacky, but it was the only way when the interface is not open. The next step was implementing a way of showing a new container row with a “More results…” label to be able to transparently carry on browsing.

Other dirty thing is that I need to override the count and skip parameters because now we have to pay attention to the pagination info and having only 64 results would be a pain in the ass. Do you imaging browsing the thousands and thousands of Jamendo artists in chunks of 64? I thought that 1024 was a much more reasonable number. Anyway a g_message is printed when the given count is overridden.

I talked to Juan about the possibility of implementing that in Grilo itself as it could be a nice of way of providing automatic pagination, but we agreed that it was better to implement the prototype at MafwGriloSource and then, if it was good enough and the model was suitable for Grilo, we could move it there.

How could I implement this? The easiest way was changing the way the MAFW object ids are build from the GrlMedia object. What we had so far, was source_uuid::media_object_id. First I thought of having a special uuid indicating that there was pagination but this would not work as MAFW really needs to parse a valid source uuid (this is, corresponding to an existing source), to send the requests to the appropriate one, so I had to discard this option.

Then, if I could not touch the source uuid, the next and only choice was the media object id. As the MAFW media object id is created directly from the GrlMedia id, it is an opaque string for us, so the best solution was adding the pagination information (the next element index in the list to request) and then catenating the media object id with a semicolon as separation. Result: source_uuid::next_element_index:current_container_media_object_id. For this, I needed to change the functions to serialize and deserialize the object id.

Once I had the pagination info, the only thing left should be changing the callback to return the data to check if there were results left and adding the row that you will see if you, for example, browse Jamendo artists.

Here you have the result:

Screenshot showing pagination

If you find anything weird, drop me a line.

I have to thank Igalia for letting use work time to finish this.