Git for Android Developers

PRESENTATION ANDEVCON • MAY 14, 2012

For the Android DeveloperTony Hillerson, AnDevCon Spring 2012#AnDevCon @tackmobile @thillersonhttp://www.slideshare.net/thillerson/git-for-android-developers

Git

http://www.slideshare.net/thillerson/git-for-android-developers

http://www.slideshare.net/thillerson/git-for-android-developers

PRESENTATION tackmobile.com

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

http://training.oreilly.com/androidapps2/





Diving Right InLearning by Doing

tackmobile.comPRESENTATION

orgitinit

changes

gitadd git commit

changes

gitadd git commit

changes

gitadd git commit

... ∞

86650c185eda50c9f9d58e2fbdf8b7113e5dee54

6facfd9f34173f4fb024196996e948a87c85eb56

b02ef5bf190e28ba24eab3ffab6133181cb5b5ef

gitclone


.gitignore

• Can be nested deeply

• https://github.com/github/gitignore

https://github.com/github/gitignore

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


master

Tagging

fb4f5d9 c5083fa 3f43fa3

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

• 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


PreliminariesGetting Git and Getting Set Up


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

Linus Torvaldshttp://en.wikipedia.org/wiki/Linus_Torvalds

http://git-scm.com

http://git-scm.com

http://git-scm.com

http://git-scm.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

http://git-scm.com

http://git-scm.com


Getting Set Up on Mac

• Homebrew - http://mxcl.github.com/homebrew/• brew install git

• MacPorts - http://www.macports.org/

http://mxcl.github.com/homebrew/

http://mxcl.github.com/homebrew/

http://www.macports.org/

http://www.macports.org/


Getting Set Up on Windows

• msysgit -http://code.google.com/p/msysgit/

http://code.google.com/p/msysgit/

http://code.google.com/p/msysgit/


Getting Set Up on Linux

• apt, etc - you probably know the drill


WIN

MAC

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

• Source Tree - Mac App Store

• Brother Bard’s GitX fork - http://brotherbard.com/blog/2010/03/experimental-gitx-fork/

• Tortoise Git - http://code.google.com/p/tortoisegit/

http://git-tower

http://git-tower

http://brotherbard.com/blog/2010/03/experimental-gitx-fork/

http://brotherbard.com/blog/2010/03/experimental-gitx-fork/

http://code.google.com/p/tortoisegit/

http://code.google.com/p/tortoisegit/


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

http://www.eclipse.org/egit/

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

http://git-scm.com/

http://git-scm.com/

http://progit.org/book/

http://progit.org/book/

http://www.pragprog.com/screencasts/v-scgithub/insider-guide-to-github





The Command LineA Short Sermon


The Guts of GitThe Little Bits that Make Git Different


What’s With all the Characters?

• SHA1 Hash

• Uniquely identifies a commit

• Secure - very unlikely that someone can tamper with content in a repository

86650c185eda50c9f9d58e2fbdf8b7113e5dee54


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

e8d5cf6579a3b1


Trees Give Structure

b84ed8ed

e8d5cf6

579a3b1

9899d2c

foo.txt

bar.txt

baz.html

3ffb35b /imagestrees can point to other trees


Commits Point to Trees

b84ed8ed

e8d5cf6

579a3b1

9899d2c

foo.txt

bar.txt

baz.html

3ffb35b /images

d414c3e“Updated the main activity”


Commits Have Parents

d414c3e

090c953

4493671

c1d1f60

“Updated the main activity”

“Fixed bug #42”

“Added RoboGuice”

“Initial commit”


Refs Point to Commits

d414c3e

090c953

4493671

c1d1f60

“Updated the main activity”

“Fixed bug #42”

“Added RoboGuice”

“Initial commit”

HEAD


And That’s All You Need To Know About

Git


(Mostly)

And That’s All You Need To Know About

Git


Sweet Moves with GitSweet, Sweet Moves


Interactive AddBuilding 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 CommitFix 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 RevertMore Like Git Reverse


git revert

• Commits the reverse of a commit

• The previous commit is still there

• != svn revert


Git StashLike a Little Repo In Your Repo


git stash

• remember: git help stash

• Stash away changes in a safe place


BranchingHitting 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


add_login_activity

master

Branching

fb4f5d9 c5083fa

9aa8827 fe594ce ccb6f5e

git checkout -b add_login_activity


add_login_activity

master

Branching: Merging

fb4f5d9 c5083fa


3f43fa3

git checkout master


git merge add_login_activity


add_login_activity

master

Branching: Rebasing

fb4f5d9 c5083fa


3f43fa3

add_login_activity

master

fb4f5d9 c5083fa


3f43fa3

after`git rebase master`

before


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 PickI’ll Take One Of Those... And One Of Those...


add_login_activity

master

Cherry-pick

fb4f5d9 c5083fa


3f43fa3

git cherry-pick fe594ce

A new commit with the changes from

fe594ce


Interactive RebaseRewrite 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/thillersonhttp://slideshare.com/thillerson

For the Android Developer • Tony Hillerson • AnDevCon Spring 2012

http://github.com/thillerson

http://github.com/thillerson

http://slideshare.com/thillerson

http://slideshare.com/thillerson

Technology

Git for Android Developers