Git for Android Developers

GitFor the Android Developer

Tony Hillerson, AnDevCon Fall 2013

#AnDevCon @tackmobile @thillerson

Presentation tackmobile.comPresentation tackmobile.com

About Me

• @thillerson, +thillerson

• Developer at Tack Mobile(tackmobile.com), @tackmobile

• Android, iOS, and Mobile Web

• Rails, Node, maybe Elixir (one day)

Diving Right InLearning by Doing

Image © Dennis Barneshttp://www.flickr.com/photos/dennisbarnes/2817664242

http://www.flickr.com/photos/dennisbarnes/2817664242

Presentation tackmobile.com

git init

changes

git add

git commit

changes

git add

git commit

changes

git add

git commit

... ∞

86650c185

6facfd9f3

b02ef5bf1

git cloneor


.gitignore

• Can be nested deeply

• 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 Torvalds http://en.wikipedia.org/wiki/Linus_Torvalds

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


Getting Set Up on Mac

• Homebrewhttp://mxcl.github.com/homebrew/

• brew install git

• MacPortshttp://www.macports.org/

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

http://www.macports.org/


Getting Set Up on Windows

• msysgithttp://code.google.com/p/msysgit/

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


Getting Set Up on Linux

• apt, etc - you probably know the drill


Gooies!

• SourceTree (Mac and Windows)http://sourcetreeapp.com/

• TortoiseGit (Windows)http://code.google.com/p/tortoisegit/

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


IDE Integration

• Android StudioYou’re All Set

• Eclipsehttp://www.eclipse.org/egit/

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


Reference

• Githttp://git-scm.com/

• ProGithttp://progit.org/book/

• Insider Guide to Github http://www.pragprog.com/screencasts/v-scgithub/insider-guide-to-github

http://git-scm.com/

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 e.g.86650c185eda50c9f9d58e2fbdf8b7113e5dee54

• 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

e8d5cf6579a3b1


Trees Give Structure

b84ed8ed

e8d5cf6

579a3b1

9899d2c

MainActivity.java

BarView.java

FooFragment.java

3ffb35b /anotherpackage

trees can point to other trees

com/yourcompany/androidapp


Commits Point to Trees

b84ed8ed

e8d5cf6

579a3b1

9899d2c

MainActivity.java

BarView.java

FooFragment.java

3ffb35b /anotherpackage

com/yourcompany/androidappd414c3e

“Fixed bug # 42”


Commits Have Parents

d414c3e

090c953

4493671

c1d1f60

“Updated the main activity”

“Fixed bug #42”

“Typed awesome code”

“Initial commit”

1

2

3

4


Refs Point to Commits

d414c3e

090c953

4493671

c1d1f60

“Updated the main activity”

“Fixed bug #42”

“Typed awesome code”

“Initial commit”

1

2

3

4HEAD


And That’s All You Need To Know About Git


And That’s All You Need To Know About Git

(Mostly)

Day to Day Git“What would you say you *do* here?”


Semantic CommitsMake Commits Mean Something


Semantic Commits

• Git’s not just a big truck

• Commits should each mean something


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


Interactive Add - SourceTree


BranchingLike Hitting Save Before You Fight the Level Boss


Branching

• New branch: git checkout -b <name>

• A branch is a named ref

• 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


master

Branching

fb4f5d9 c5083fa

add_login_activity

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`

• … but don’t


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`


Git StashLike a Little Repo In Your Repo


git stash

• remember: git help stash

• Stash away changes in a safe place

• A Workflow:Stash -> Fix & Commit -> Pop Stash


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


Cherry Pick

• When you need a commit’s changes

• But not its history


add_login_activity

master

Cherry-pick

fb4f5d9 c5083fa


git cherry-pick fe594ce

3f43fa3

A new commit with the changes

from fe594ce


Whoops!Lots Of Ways To Fix It


git checkout

• `git checkout [filename] ̀=remove unstaged changes


git revert

• Commits the reverse of a commit

• The previous commit is still there

• != svn revert


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


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


git reset

• `git reset [filename]` = opposite of `git add [filename]`

• `git reset HEAD` = same as above - acts on all tracked changes

• `git reset HEAD^` (also ^^, or ~1, ~42, etc.) = rollback commits to working tree

• All examples of “mixed” reset


git reset --soft [commit]

1. Moves HEAD to [commit]

2. Puts the “popped” contents on the index


git reset [commit] (“mixed” - default)



3. Moves the index’s changes to the working tree

4. Clears the index


git reset --hard [commit] (DESTRUCTIVE!!!)



3. Moves the index’s changes to the working tree

4. Clears the index

5. Makes the working copy look like the index


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 different branch!


Git FlowA Popular Branching Model


Git Flow

• Conventions to follow

• Tools to help you follow conventions

• http://nvie.com/posts/a-successful-git-branching-model/

http://nvie.com/posts/a-successful-git-branching-model/


Git Flow Conventions: Master Branch

• The master branch is what is publicly available now

• You don’t commit directly to master


Git Flow Conventions: Develop Branch

• A branch called “develop” is what will become the next version

• Day to day work happens on develop

• “Integration branch”


Git Flow Conventions: Feature Branches

• Long running development go on feature branches: “feature/foo”

• Long running: “more than one commit”

• Can be pushed to the server and shared

• Branch from develop


Git Flow Conventions: Hotfixes

• OMG Problems in Production, create a hotfix: “hotfix/foo”

• Branch from master (not develop)


Git Flow Conventions: Releases

• When a release is almost ready on develop, create a release branch: “release/2.0.4”

• Branch from develop

• Develop continues on for the next release

• Small changes to release go on release branch


Branch Lifecycle

• Features

• Start from develop

• Finished and merged to develop

• Releases

• Start from develop

• Finished and merged to master and develop


Git Flow in Action: Features

feature/somefeature

master

develop


Git Flow in Action: Releases

release/v1.0

master

develop


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!Git for the Android Developer • Tony Hillerson

• Questions?

• We’re Hiring! [email protected]

• Excellent Team

• Awesome Projects

• Great Office

mailto:[email protected]

Technology

Git for Android Developers