xkcd viewer report

1. COMS 6998-7 Celluar Networks and Mobile Computing
Final Project Report
Bocheng Zhou bz2228
1. Motivation
For this final project, I wanted to gain more experience in android development. And
since I'm the only team member of my team, I wanted to implement something
interesting and useful to me. Finally, I decided to implement an xkcd viewer, because
I'm a huge fan of this nerdy and ridiculously profound webcomic, and have always
wanted a convenient app to browse the comics easily. Moreover, I thought I would learn
a lot of new android stuff along the way.
2. Problem statement & proposed solution
First of all, I wanted my app to have the basic functionalities like those on the xkcd
website: when the app boots, it will fetch me the latest xkcd comic. I can browse the
next comic, the previous one, the last one, the first one, and, if I'm feeling lucky, a
random one. Second, there is this awesome website called “explain xkcd”, which, not
surprisingly, explains to you in great detail the actually meaning behind the comics if
you find some of them hard to understand. And it would be great to integrate this into
the app. Third, I want to “favorite” the comics, because some of them(or almost all of
them) are hilarious and enlightening. And I really like the concept of circles in the
google+ app, so I thought it would be neat if I can “circle” the comics(make them
belong to one or more categories) as a way of favoriting them.
To implement those functionalities, the android actionbar will be a natural choice, since
it provides a clean user interface and a bunch of intuitive options. And there will be a tab

2. bar with two tabs, one for displaying the comic and the other displaying the list of
favorited comics.
3. Design and Architecture
One of the essential design issues is that avoid sending http requests as much as
possible. As has mentioned in the lectures, energy bugs contribute significantly to high
battery usage. In terms of power consumption, many components of the phone have very
high tail states even after they stop the service, and wifi/network connection is one of
them. A typical scenario is that the user may want to go back to the previous
comics they've seen, which have already been downloaded, so it is not necessary to
download them again. In other words, I should cache the images. When the user goes
back to a previous comic, the app should just load it from the cache.
The app's main activity is an action-bar activity with two tab bars embedded in it. With
the help of viewpager, the user can swipe back and forth between the 2 tab bars. The 2
tab bars are subclasses of android fragments. The first tab bar contains an image view,
which will display the comic once it is downloaded, and 5 buttons which the user can
press them to wade through all the comics. The second bar is a listview, whose items are
comprised of the titles, connotations and the tags of the favorited comics. The action
bar provide the options like favorite, share and explain.
4. Implementation and testing
There app will use the REST api porvided by xkcd, which will fetch the metadata of the
comics in JSON format. One of the import libraries used in the project is Picasso, which
is a powerful image downloading and caching library for android. I first tried to
implement my own caching of images, but it turned out to be error-prone. Picasso did a
really great job caching the images:when the user go back to previously downloaded

3. comics, it loads instantly, the speedup is very noticeable. Another library used in this
project is PhotoView, which is for image zooming and pinching. The user can pinch to
zoom in or zoom out the comic image smoothly.
For storing the tags across different sessions, I used the Shared Preference, which is the
most suitable storage option for this task.
For testing, the Logcat is the most helpful during the process of doing this project. One
can assign tags to the log messages, and logcat provides filtering based on keywords and
saving the log to a file, which had been very useful for analyzing the behavior of the
program.
5. Lessons learned
1.Start early and join a team. When I started to do the project, it had been over a month
since the last android homework. I basically needed to relearn quite a few things before I
could go on with more advanced stuff. Given the time constraints, I could not implement
a more sophisticated app, which is a shame. I think if I had joined another team instead
of working alone, I could have learned faster and have added more complex
functionalities to the app.
2. Don't reinvent the wheel. Before using the Picasso library, I tried to implement image
caching myself, which is error-prone and time consuming. Using full-fledged libraries
will make the development faster and the app more robust.
3. Make sure to initialize the objects correctly, and always beware of the possibility of
the object being null. Actually many of the bugs can be attributed to null pointer
exception.

4. 4. Learn and understand the life cycle of Fragments, Activity, etc. Fully understanding
these things will save you a lot of time which would otherwise be used on unncessary
tial and error.
6. Summary and further work
Although the project doesn't look as sophisticated as those of other teams, but I did learn
a lot about android programming. For further work, I think I can add more advanced
features to the app. I'm actually planning on adding social elements into the app, such as
see how your facebook friends tag the comic you have favorited, try to find the people
who are similar to you based on the tags they given to the comics.
Extra Remarks
Dear Professor Li, Xiao and William, I'm so sorry I missed the presentation which I
should have given. Before the class, I'd only slept for 4 hours in 2 days, so I'm very sleep
deprived. I fell asleep unconsciously and woke up only to find I already missed the
presentation time. But this report is basically the transcript of what I was going to say in
the presentation, and I also included a video to showcase the app.
I know it's totally my fault to miss the presentation and turn in the project late. But I
swear I did it all by myself and did put a lot of time and effort into it. Any grade is
acceptable for me. Please don't fail me!