Android Handbook | Building quality apps / Naming

Naming

Last modified on Thu 09 Nov 2023

Good naming makes it easier to read and understand code.

Consider the following two versions of functionally equivalent code.

val list1 = arrayListOf<String>()
list2.forEach { x ->
  if(x.length <= 4) {
    list1.add(x)
  }
}
return list1

val shortFileNames = arrayListOf<String>()
fileNames.forEach { name ->
  if (name.length <= FILE_NAME_LENGTH_LIMIT) {
    shortFileNames.add(name)
  }
}
return shortFileNames

Which one is more understandable?

To make your code understandable, you need to reveal your intent and avoid disinformation.

Methods which return boolean values should sound like questions.

if (isFileTooLarge(image))

is more readable than

if (checkFileSize(image))

Naming conventions

All code is written in English, including comments.
Upper CamelCase is used for classes.
Lower camelCase is used for methods, local variables, and instance variables.
Abbreviations and acronyms should use camel case as normal words (e.g., XmlHttpRequest, QrCodeReader, userId).
Constants should be ALL_CAPS.
Methods are named after verbs, variables and classes after nouns.
XML resource IDs have to use snake_case.
XML resource IDs should use camelCase in a Kotlin project.
Activities and fragments are named with the appropriate suffix: LoginActivity, RegisterFragment.
The corresponding layouts have to be named with the appropriate prefix: activity_login.xml, fragment_register.xml.
All naming has to be simple, clear and mnemonic (short and meaningful).
The Infinum Code Style has to be imported into the Android Studio and used in formatting code. If you want to find out how to import it, check out the chapter about Development environment setup.
Drawable resources also have naming conventions.

Examples of good naming

class WelcomeActivity : BaseActivity, WelcomeView {

    @InjectView(R.id.viewExchangeQuote)
    protected var exchangeQuoteView: ExchangeQuoteView? = null

    @InjectView(R.id.textSeeDetails)
    protected var seeDetailsText: TextView? = null

    @OnClick(R.id.textSeeDetails)
    protected fun onSeeDetailsClicked() {
        presenter.onDetailsRequested()
    }

    @OnClick(R.id.loginButton)
    protected fun onLoginButtonClicked() {
        presenter.onLoginButtonClicked()
    }

    @OnClick(R.id.registerButton)
    protected fun onRegisterButtonClicked() {
        presenter.onRegisterButtonClicked()
    }

    override fun showCurrencies(currencies: List<Currency>) {
        exchangeQuoteView.showCurrencies(currencies)
    }

    override fun showSellingAmount(sellingAmount: String) {
        exchangeQuoteView.showSellingAmount(sellingAmount)
    }

    override fun showBuyingAmount(buyingAmount: String) {
        exchangeQuoteView.showBuyingAmount(buyingAmount)
    }

    override fun navigateToLogin() {
        val intent = Intent(this, LoginActivity::class.java)
        startActivityForResult(intent, REQUEST_CODE_LOGIN)
    }

    override fun navigateToRegister() {
        val intent: Intent = RegistrationActivity.buildIntent(this)
        startActivityForResult(intent, REQUEST_CODE_REGISTER)
    }

    companion object {
        const val REQUEST_CODE_LOGIN = 147
        const val REQUEST_CODE_REGISTER = 148
        const val EXTRA_ACTION = "EXTRA_ACTION"
    }
}

<ScrollView 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">

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

        <co.infinum.currencyfair.custom.ExchangeQuoteView
            android:id="@+id/viewExchangeQuote"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:visibility="invisible"
            tools:visibility="visible"/>

        <com.ivankocijan.magicviews.views.MagicTextView
            android:id="@+id/textSeeDetails"
            style="@style/TextButton"
            android:padding="8dp"
            android:textAllCaps="false"
            tools:text="@string/see_how_you_save"
            android:visibility="invisible"
            tools:visibility="visible"/>

        <Space
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"/>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal">

            <com.ivankocijan.magicviews.views.MagicButton
                android:id="@+id/registerButton"
                style="@style/AppTheme.Button"
                android:layout_width="0dp"
                android:layout_weight="0.5"
                android:layout_marginRight="8dp"
                android:text="@string/register"/>

            <Space android:layout_width="16dp"
                android:visibility="gone"
                android:layout_height="1dp"/>

            <com.ivankocijan.magicviews.views.MagicButton
                android:id="@+id/loginButton"
                style="@style/AppTheme.Button"
                android:layout_width="0dp"
                android:layout_weight="0.5"
                android:text="@string/login"/>

        </LinearLayout>
    </LinearLayout>
</ScrollView>