Android Guidelines

File Naming

(Source, access at 04.12.19)

Class files

• Class names are written in UpperCamelCase
• Classes that extend an Android component, the name of the class should end with name of component (e.g. SignInActivity, SignInFragment, ImageUploaderService, ChangePasswordDialog)

Drawable files

Naming conventions for drawables

Type	Prefix
Button	btn_
Text View	tv_
Card View	cv_
List View	lv_
Image View	img_
Edit Text	et_
Check Box	chk_
Action Bar	ab_
Progress Bar	pb_
Dialog	dialog_
Menu	menu_
Notification	notification_
Radio Button	rb_
Toggle Button	tb_
Icon	ic_
Launcher Icon	ic_launcher_
Menu & Action Bar Icon	ic_menu_
Status Bar Icon	ic_stat_notify_
Tab Icon	ic_tab_
Dialog Icon	ic_dialog_

Naming conventions for selector state

State	Suffix
Normal	_normal
Pressed	_pressed
Focused	_focused
Disabled	_disabled
Selected	_selected

Values files

• Resources file names: lowercase_underscore
• Ressource files in value folders should be plural strings.xml, styles.xml, dimens.xml, attrs.xml

Layout Files

Component	Class Names	Layout Name
Activity	UserProfileActivity	activity_user_profile
Fragment	SignUpFragment	fragment_sign_up
Dialog	ChangePasswordDialog	dialog_change_password
Adapter View Item	---	item_personal
Partial Layout	---	partial_stats_bar

Code Guidelines

XML Style Rules

ID naming

(Source, access at 04.12.19) IDs should be prefixed with the name of the element in lowercase underscore

WHAT	WHERE	DESCRIPTION
name of Android/Custom view class (e.g. Button --> btn_)	activity separated without activity_ (e.g. activity_select_measurement_input --> _ select_measurement_input_)	differentiate multiple elements in one screen (e.g. is a Button for saving --> _save)

--> btn_select_measurement_input_save

Attribute ordering

(Source, access at 04.12.19) Try to group similar attributes together

1. View Id
2. Style
3. Layout width and height
4. Other layout attributes, sorted alphabetically
5. Remaining attributes, sorted alphabetically

Java Style Rules

Naming and fields definition

Fields should be defined at the top of the file

• Private, non-static field names start with m
• Private, static field names start with s
• Other fields start with a lower case letter
• Static final fields (constants) are ALL_CAPS_WITH_UNDERSCORES
• Struct/union field names use lowerCamelCase
• Interface names must start with an I followed by an UpperCamleCase / PascalCase name
• Function names, arguments, return variables use lowerCamelCase

Treat acronyms as words

Good	Bad
XMLHttpRequest	XMLHTTPRequest
getCustomerId	getCustomerID
String url	String URL
long id	long ID

Use TODO comments

(Source, access at 04.12.19)

• For code that is temporary, a short-term solution, or good-enough but not perfect
• Should include the tring TODO in all caps, followed by a colon: and

Use spaces for identation

(Source, access at 04.12.19)

Use 4 space indents for blocks (never tabs)

Use 8 space indents for line wraps, including function calls and assignments

Use standard brace style

Braces go on the same line as the code before them, they don’t go on their own line

Braces around the statements are required unless the condition and the body fit on one line

Logging guidelines

• Log.v(String tag, String msg) (verbose)
• Log.d(String tag, String msg) (debug)
• Log.i(String tag, String msg) (information)
• Log.w(String tag, String msg) (warning)
• Log.e(String tag, String msg) (error)

Class member ordering

Logical and consistant order

1. Constants
2. Fields
3. Constructors
4. Override methods and callbacks (public or private)
5. Public methods
6. Private methods
7. Inner class or interfaces

String constants, naming values

When using one of the these components, you must define the keys as a statical final fields and they should be prefixed as indicated below.

Element	Field Name Prefix
SharedPreferences	PREF_
Bundle	BUNDLE_
Fragment Arguments	ARGUMENT_
Intent Extra	EXTRA_
Intent Action	ACTION_

Formatting

(Source, access at 04.12.19)

• Whitespaces: no trailing whitespace on lines; empty lines must not contain whitespaces
• Spaces vs. tabs: use only spaces

Line length limit

(Source, access at 04.12.19)

• Not exceed 100 characters
• If line is longer than this limit there are usually two options to reduce ist length: ** Extract a local variable or method (preferable) ** Apply line-wrapping to divide a single line into multiple ones
• There are two exceptions where it is possible to have lines longer than 100: ** Lines that are not possible to split, e.g. long URLs in comments ** package and import statements