Lessons learned from Android developers in Futurice. Avoid reinventing the wheel by following these guidelines. If you are interested in iOS or Windows Phone development, be sure to check also our iOS Good Practices and Windows App Development Best Practices documents.

Android SDK

Build system

• Build different flavours or variants of your app
• Make simple script-like tasks
• Manage and download dependencies
• Customize keystores
• And more

Project structure

old-structure
├─ assets
├─ libs
├─ res
├─ src
│  └─ com/futurice/project
├─ AndroidManifest.xml
├─ build.gradle
├─ project.properties
└─ proguard-rules.pro

new-structure
├─ library-foobar
├─ app
│  ├─ libs
│  ├─ src
│  │  ├─ androidTest
│  │  │  └─ java
│  │  │     └─ com/futurice/project
│  │  └─ main
│  │     ├─ java
│  │     │  └─ com/futurice/project
│  │     ├─ res
│  │     └─ AndroidManifest.xml
│  ├─ build.gradle
│  └─ proguard-rules.pro
├─ build.gradle
└─ settings.gradle

Gradle configuration

signingConfigs {
    release {
        storeFile file("myapp.keystore")
        storePassword "password123"
        keyAlias "thekey"
        keyPassword "password789"
    }
}

KEYSTORE_PASSWORD=password123
KEY_PASSWORD=password789

signingConfigs {
    release {
        try {
            storeFile file("myapp.keystore")
            storePassword KEYSTORE_PASSWORD
            keyAlias "thekey"
            keyPassword KEY_PASSWORD
        }
        catch (ex) {
            throw new InvalidUserDataException("You should define KEYSTORE_PASSWORD and KEY_PASSWORD in gradle.properties.")
        }
    }
}

dependencies {
    compile 'com.squareup.okhttp:okhttp:2.2.0'
    compile 'com.squareup.okhttp:okhttp-urlconnection:2.2.0'
}

android {
    buildTypes {
        debug {
            applicationIdSuffix '.debug'
            versionNameSuffix '-DEBUG'
        }

        release {
            // ...
        }
    }
}

IDEs and text editors

Libraries

dependencies {
    classpath 'me.tatarka:gradle-retrolambda:2.4.1'
}

apply plugin: 'retrolambda'

android {
    compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}

retrolambda {
    jdk System.getenv("JAVA8_HOME")
    oldJdk System.getenv("JAVA7_HOME")
    javaVersion JavaVersion.VERSION_1_7
}

• Any interface with just one method is "lambda friendly" and can be folded into the more tight syntax
• If in doubt about parameters and such, write a normal anon inner class and then let Android Studio fold it into a lambda for you.

Activities and Fragments

• Avoid using nested fragments extensively, because matryoshka bugs can occur. Use nested fragments only when it makes sense (for instance, fragments in a horizontally-sliding ViewPager inside a screen-like fragment) or if it's a well-informed decision.
• Avoid putting too much code in activities. Whenever possible, keep them as lightweight containers, existing in your application primarily for the lifecycle and other important Android-interfacing APIs. Prefer single-fragment activities instead of plain activities - put UI code into the activity's fragment. This makes it reusable in case you need to change it to reside in a tabbed layout, or in a multi-fragment tablet screen. Avoid having an activity without a corresponding fragment, unless you are making an informed decision.
• Don't abuse Android-level APIs such as heavily relying on Intent for your app's internal workings. You could affect the Android OS or other applications, creating bugs or lag. For instance, it is known that if your app uses Intents for internal communication between your packages, you might incur multi-second lag on user experience if the app was opened just after OS boot.

Java packages architecture

com.futurice.project
├─ network
├─ models
├─ managers
├─ utils
├─ fragments
└─ views
   ├─ adapters
   ├─ actionbar
   ├─ widgets
   └─ notifications

Resources

• One attribute per line, indented by 4 spaces
• android:id as the first attribute always
• android:layout_**** attributes at the top
• style attribute at the bottom
• Tag closer /> on its own line, to facilitate ordering and adding attributes.
• Rather than hard coding android:text, consider using Designtime attributes available for Android Studio.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    >

    <TextView
        android:id="@+id/name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:text="@string/name"
        style="@style/FancyText"
        />

    <include layout="@layout/reusable_part" />

</LinearLayout>

• android:id should obviously be in the layout files
• android:orientation for a LinearLayout normally makes more sense in layout files
• android:text should be in layout files because it defines content
• Sometimes it will make sense to make a generic style defining android:layout_width and android:layout_height but by default these should appear in the layout files

<style name="ContentText">
    <item name="android:textSize">@dimen/font_normal</item>
    <item name="android:textColor">@color/basic_black</item>
</style>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/price"
    style="@style/ContentText"
    />

<resources>
    <color name="button_foreground">#FFFFFF</color>
    <color name="button_background">#2A91BD</color>
    <color name="comment_background_inactive">#5F5F5F</color>
    <color name="comment_background_active">#939393</color>
    <color name="comment_foreground">#FFFFFF</color>
    <color name="comment_foreground_important">#FF9D2F</color>
    ...
    <color name="comment_shadow">#323232</color>

<resources>

    <!-- grayscale -->
    <color name="white"     >#FFFFFF</color>
    <color name="gray_light">#DBDBDB</color>
    <color name="gray"      >#939393</color>
    <color name="gray_dark" >#5F5F5F</color>
    <color name="black"     >#323232</color>

    <!-- basic colors -->
    <color name="green">#27D34D</color>
    <color name="blue">#2A91BD</color>
    <color name="orange">#FF9D2F</color>
    <color name="red">#FF432F</color>

</resources>

<resources>

    <!-- font sizes -->
    <dimen name="font_larger">22sp</dimen>
    <dimen name="font_large">18sp</dimen>
    <dimen name="font_normal">15sp</dimen>
    <dimen name="font_small">12sp</dimen>

    <!-- typical spacing between two views -->
    <dimen name="spacing_huge">40dp</dimen>
    <dimen name="spacing_large">24dp</dimen>
    <dimen name="spacing_normal">14dp</dimen>
    <dimen name="spacing_small">10dp</dimen>
    <dimen name="spacing_tiny">4dp</dimen>

    <!-- typical sizes of views -->
    <dimen name="button_height_tall">60dp</dimen>
    <dimen name="button_height_normal">40dp</dimen>
    <dimen name="button_height_short">32dp</dimen>

</resources>

<string name="network_error">Network error</string>
<string name="call_failed">Call failed</string>
<string name="map_failed">Map loading failed</string>

<string name="error.message.network">Network error</string>
<string name="error.message.call">Call failed</string>
<string name="error.message.map">Map loading failed</string>

<string name="error.message.call">CALL FAILED</string>

<string name="error.message.call">Call failed</string>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    >

    <RelativeLayout
        ...
        >

        <LinearLayout
            ...
            >

            <LinearLayout
                ...
                >

                <LinearLayout
                    ...
                    >
                </LinearLayout>

            </LinearLayout>

        </LinearLayout>

    </RelativeLayout>

</LinearLayout>

Test frameworks

solo.sendKey(Solo.MENU);
solo.clickOnText("More"); // searches for the first occurrence of "More" and clicks on it
solo.clickOnText("Preferences");
solo.clickOnText("Edit File Extensions");
Assert.assertTrue(solo.searchText("rtf"));

Emulators

Proguard configuration

buildTypes {
    debug {
        minifyEnabled false
    }
    release {
        signingConfig signingConfigs.release
        minifyEnabled true
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}

1. ProGuard has removed the class, enum, method, field or annotation, considering it's not required.
2. ProGuard has obfuscated (renamed) the class, enum or field name, but it's being used indirectly by its original name, i.e. through Java reflection.

-keep class com.futurice.project.MyClass { *; }

-keepnames class com.futurice.project.MyClass { *; }

Data storage

SharedPreferences

• Performance: Your data is complex or there is a lot of it
• Multiple processes accessing the data: You have widgets or remote services that run in their own processes and require synchronized data

ContentProviders

Using an ORM

Use Stetho

Thanks to