Git for Android Developers

Git
For the Android Developer
Tony Hillerson, AnDevCon Spring 2012
#AnDevCon @tackmobile @thillerson
http://www.slideshare.net/thillerson/git-for-android-developers
PRESENTATION ANDEVCON • MAY 14, 2012

About Me
• Worked with Android and Git for a few years now
• O’Reilly Screencaster: Developing Android Applications
• http://training.oreilly.com/androidapps/
• http://training.oreilly.com/androidapps2/
• Tech Reviewer

PRESENTATION tackmobile.com

Diving Right In
Learning by Doing


git git
or clone
init

git
git commit 86650c185eda50c9f9d58e2fbdf8b7113e5dee54
changes add

git
git commit 6facfd9f34173f4fb024196996e948a87c85eb56
changes add

git
git commit b02ef5bf190e28ba24eab3ffab6133181cb5b5ef
changes add

... ∞


.gitignore
• Can be nested deeply
• https://github.com/github/gitignore


Git Log - The Project’s History
• What got committed?
• Commit messages
• Content
• When? Who?


Remotes
• remote add
• clone
• fetch
• pull
• push


Tagging
git tag -a -m"Tagging v1.0" v1.0 c5083fa

master

fb4f5d9 c5083fa 3f43fa3

• Both “-v1.0” and c5083fa will point to c5083fa

• Push this tag with `git push --tags`

• Can be cryptologically signed

Recap of Simple Commands
• git init - Creates an empty Git repository
• git add - Adds a file to the stage (“stages a file”)
• git rm - Removes from version control
• git commit - Commits the staged changes to the (local) repository
• git log - A view of the history
• git tag - Names a commit
• .gitignore - tells git to ignore certain files


Why Source Control?
• For the solo developer?
• Protection against mistakes
• Freedom
• ... to refactor
• ... to experiment
• For the development team?
• All of the above, plus:
• Parallel development
• Merging different code branches


Preliminaries
Getting Git and Getting Set Up


What’s a Git?
A completely ignorant, childish person with no
manners. - http://urbandictionary.com

Linus Torvalds
PRESENTATION http://en.wikipedia.org/wiki/Linus_Torvalds tackmobile.com

What’s a Git?

Git is a free & open source, distributed
version control system designed to handle
everything from small to very large projects
with speed and efficiency.
- http://git-scm.com


Getting Set Up on Mac
• Homebrew - http://mxcl.github.com/homebrew/
• brew install git

• MacPorts - http://www.macports.org/


Getting Set Up on Windows
• msysgit -http://code.google.com/p/msysgit/


Getting Set Up on Linux
• apt, etc - you probably know the drill


Gooies!
Git Tower - http://git-tower.com
M
•

• Source Tree - Mac App Store A
• Brother Bard’s GitX fork - http://brotherbard.com/blog/2010/03/experimental-gitx-fork/ C
• Tortoise Git - http://code.google.com/p/tortoisegit/ W
I
N


Eclipse Integration
• http://www.eclipse.org/egit/


Reference
• Git - http://git-scm.com/
• ProGit - http://progit.org/book/ - Scott Chacon
• Insider Guide to Github -
http://www.pragprog.com/screencasts/v-scgithub/insider-guide-to-
github - Scott Chacon


The Command Line
A Short Sermon


The Guts of Git
The Little Bits that Make Git Different


What’s With all the Characters?
86650c185eda50c9f9d58e2fbdf8b7113e5dee54
• SHA1 Hash
• Uniquely identifies a commit
• Secure - very unlikely that someone can tamper with content in a
repository


SHA-1 Hash Keys

“ ... to have a probability of a SHA1-hash
collision rise to 1/2, you need about
10^24 objects ...
- Scott Chacon in Pro Git (paraphrased)


In Git There Are Only...
• Blobs
• Trees
• Commits


Blobs
• The contents of your files are stored as binary files in .git/objects
• Git is efficient. It only stores the same content once.
• Identified by a SHA-1
• Show blob contents with e.g. git show c7fb9f5


Trees
• Trees give structure to blobs
• Trees are also stored in .git/objects
• Identified by SHA-1
• View a tree with ls-tree, e.g. `git ls-tree HEAD`


Commits
• Identified by a SHA-1
• Points to one tree
• Has a required message
• May have one (or more) parent commit(s)
• Show the reachable commits from a commit: git rev-list HEAD


Refs
• Point to commits
• .git/refs/heads - the latest commits in local branches
• HEAD - the latest commit on the current branch


Blobs Are Content

b84ed8ed

e8d5cf6
579a3b1


Trees Give Structure
9899d2c

b84ed8ed foo.txt

579a3b1 bar.txt

e8d5cf6 baz.html
trees can point
3ffb35b /images to other trees


Commits Point to Trees

d414c3e 9899d2c
“Updated the main activity”

b84ed8ed foo.txt

579a3b1 bar.txt

e8d5cf6 baz.html

3ffb35b /images


Commits Have Parents

d414c3e

090c953
“Fixed bug #42”

4493671
“Added RoboGuice”

c1d1f60
“Initial commit”


Refs Point to Commits

HEAD d414c3e

090c953
“Fixed bug #42”

4493671
“Added RoboGuice”

c1d1f60
“Initial commit”


And That’s All You
Need To Know About
Git


And That’s All You
Need To Know About
Git
(Mostly)


Sweet Moves with Git
Sweet, Sweet Moves


Interactive Add
Building Semantic Commits


Interactive Add - Building Semantic Commits
• `git add` simply adds to the stage
• `git commit -a` will commit all changes to tracked files (add and
commit)
• `git add -i` -- a command line tool to interactively add changes
• Individual commits shouldn’t leave things broken
• Try to commit some useful feature or bug fix all together


Amending A Commit
Fix the Last Commit


git commit --amend
• Oops! I misspelled something in the commit message
• Oops! I did `git commit -a` and forgot to `git add` a file
• Oops! I just committed a bug
• USE ONLY BEFORE YOU SHARE CHANGES


Git Revert
More Like Git Reverse


git revert
• Commits the reverse of a commit
• The previous commit is still there
• != svn revert


Git Stash
Like a Little Repo In Your Repo


git stash
• remember: git help stash
• Stash away changes in a safe place


Branching
Hitting Save Before You Fight the Level Boss


Branching
• checkout -b
• merging
• rebasing


How To Think About Branching
• Mainline
• What do you want “master” to mean?
• Topic Branches
• Branching examples


Topic Branches
• Branching is about controlling feature sets
• Make a new branch for a story
• Make a new branch for a bug fix
• Make a new branch to spike something


Team Branching Strategies
• What do you want “master” to mean?
• Keep master deployable?
• one strategy for web software
• Use “master” as an integration branch?
• Each developer uses topic branches and integrates to master
• Make a branch for releases


Branching
git checkout -b add_login_activity

master

fb4f5d9 c5083fa

add_login_activity

9aa8827 fe594ce ccb6f5e


Branching: Merging
git checkout master
git merge add_login_activity

master


add_login_activity



Branching: Rebasing
master


add_login_activity

before 9aa8827 fe594ce ccb6f5e

master


add_login_activity

after 9aa8827 fe594ce ccb6f5e
`git rebase master`

Branching: Rebasing
• Better than merging in some ways...
• Don’t use if you’ve pushed your branch to a remote
• Can override with `git push -force`


Git Pull --rebase
• Also available: `git pull --rebase`
• Helpful for avoiding merge commits
• May cause problems if git can’t automatically merge
• `git reset HEAD` and start over with normal `git pull`


Cherry Pick
I’ll Take One Of Those... And One Of Those...


Cherry-pick
git cherry-pick fe594ce
A new commit with
master the changes from
fe594ce


add_login_activity



Interactive Rebase
Rewrite History


Interactive Rebase - Fixing History
• git rebase -i [commit]
• A list of all commits in the current order
• Reorder
• Fix a certain commit
• Squash commits together
• Delete commits
• DON’T USE AFTER YOU’VE PUSHED


Whoops!
Lots Of Ways To Fix It


git checkout
• `git checkout [filename]` = remove all unstaged changes


git reset
• `git reset [filename]` = opposite of `git add [filename]`
• `git reset HEAD` = same as above - acts on all changes
• `git reset HEAD^` (also ^^, or ~1, ~42, etc.) = rollback commits to
working tree
• All examples of “mixed” reset


git reset soft
• git reset --soft [commit]
• Moves HEAD to commit
• Puts the “popped” contents on the index


git reset mixed (default)
• git reset [commit]
• Moves the index to the working tree as changes


git reset hard
• git reset --hard [commit]
• Moves the index to the working tree as changes
• Makes the working tree look like the index
• DESTRUCTIVE


git reset use cases
• Back that last commit up (git reset HEAD^)
• Don’t forget `commit --amend`
• Oops, didn’t mean to commit that file
• I meant that commit to be on a branch!


The Take Home
• SCM Is Important
• No matter what kind of developer you are
• Git is fundamentally different from the others
• It’s not a database of patches
• It’s a history of filesystem snapshots
• It gives you freedom to innovate, make mistakes, and collaborate.


Thank you!
#AnDevCon
@tackmobile
@thillerson
http://github.com/thillerson
http://slideshare.com/thillerson

For the Android Developer • Tony Hillerson • AnDevCon Spring 2012

Git for Android Developers

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