SQLDelight 1.x Quick Start Guide for Android

SQLDelight is most well known as a Kotlin multiplatform database library. As an Android Developer, the most compelling reasons to use SQLDelight are:

  • Kotlin first
  • SQL first
  • Typesafe generated code
  • Unit tests don’t require an Android device

Documentation for how to use SQLDelight on just Android (without Kotlin mutliplatform) is lacking, so I wanted to create this guide to get people going fast on just Android.  This example is here to get you started, but does not reflect best coding practices.  I did this in order to make this quick start guide concise, and approachable.

1) Add Gradle Plugin to the buildscript classpath

In your project’s root build.gradle file, add the following dependency under buildscript dependencies.

classpath "com.squareup.sqldelight:gradle-plugin:1.1.4"

2) Apply the Gradle Plugin to your App or Module

You need to add the SQLDelight Gradle Plugin to your app or module because SQLDelight uses code generation from SQL files (*.sq), instead of code generation based on annotations (kapt).  This gives us incremental builds, but requires us to add a plugin to our root build.gradle file.  By doing code generation from SQL files, SQLDelight can generate code that works on any platform, because at the end of the day you are just executing SQL statements.

apply plugin: "com.squareup.sqldelight"

3) Add/Write the SQL (.SQ) File

You need to create a source folder for your SQL (*.sq) files at “src/main/sqldelight” folder, next to “java” or “kotlin” source folder. In this example, we’ll be representing a “item” in a shopping cart (Example from Shopping App) and the ItemInCartEntity.sq file in the following location:

MODULE_OR_APP/src/main/sqldelight/com/handstandsam/sqldelightquickstart/ItemInCartEntity.sq

ItemInCartEntity.sq

CREATE TABLE itemInCart (
    label TEXT NOT NULL UNIQUE PRIMARY KEY,
    image TEXT NOT NULL,
    quantity INTEGER NOT NULL DEFAULT 0,
    link TEXT
);

selectAll:
SELECT *
FROM itemInCart
ORDER BY label;

insertOrReplace:
INSERT OR REPLACE INTO itemInCart(
  label,
  image,
  quantity,
  link
)
VALUES (?, ?, ?, ?);

selectByLabel:
SELECT *
FROM itemInCart
WHERE label = ?;

empty:
DELETE FROM itemInCart;

deleteByLabel:
DELETE
FROM itemInCart
WHERE label = ?;

4) Install the SQLDelight Android Studio Plugin

The Android Studio Plugin is not required, but is super helpful for syntax highlighting, code completion, warnings and navigation.

.sq file without the SQLDelight Android Studio Plugin

Adding the SQLDelight Android Studio Plugin

A .sq file after the SQLDelight Android Studio Plugin is Installed

5) Add the Dependency Used for in Memory Unit Tests

You need the JdbcSqliteDriver for Unit Tests. This allows you to run your database tests without Android device. This means blazing fast tests without the hassle of connecting a device!

Add the following Unit Test dependency:

testImplementation "com.squareup.sqldelight:sqlite-driver:1.1.4"

Note: You don’t have to write unit tests and could technically skip this and the next step, but do yourself the favor and write tests from the beginning.

6) Write Unit Tests

Now that everything is set up, you should write a unit test that runs on your computer to make sure it’s all working.  This is a huge benefit over the Room library that comes with Android Jetpack because we can completely decouple ourselves from knowing what Android is.  This allows us to verify our setup and to have a quick feedback loop to ensure everything is working.

Use the JdbcSqliteDriver for an in memory version of your database for unit tests to avoid state between tests. However, be sure to also call Database.Schema.create(sqlDriver) or your in memory tests will not work. In order to make sure I call it, I use an “apply” to make sure I do it along with creating an instance of the driver.

private val inMemorySqlDriver = JdbcSqliteDriver(JdbcSqliteDriver.IN_MEMORY).apply {
    Database.Schema.create(this)
}

Here is the full ItemDatabaseTest.kt file containing the Unit Test.

package com.handstandsam.sqldelightquickstart

import com.squareup.sqldelight.sqlite.driver.JdbcSqliteDriver
import org.junit.Assert.assertEquals
import org.junit.Test

class ItemDatabaseTest {

    private val inMemorySqlDriver = JdbcSqliteDriver(JdbcSqliteDriver.IN_MEMORY).apply {
        Database.Schema.create(this)
    }

    private val queries = Database(inMemorySqlDriver).itemInCartEntityQueries

    @Test
    fun smokeTest() {
        val emptyItems: List = queries.selectAll().executeAsList()
        assertEquals(emptyItems.size, 0)

        queries.insertOrReplace(
            label = "Pineapple",
            image = "https://localhost/pineapple.png",
            quantity = 5,
            link = null
        )

        val items: List = queries.selectAll().executeAsList()
        assertEquals(items.size, 1)

        val pineappleItem = queries.selectByLabel("Pineapple").executeAsOneOrNull()
        assertEquals(pineappleItem?.image, "https://localhost/pineapple.png")
        assertEquals(pineappleItem?.quantity?.toInt(), 5)
    }
}

7) Add the SQLDelight Android Driver Dependency

Now that we have the plugin working and unit tests passing, we need to integrate with our Android app. Add this “implementation” AndroidSqliteDriver dependency on SQLDelight.

implementation "com.squareup.sqldelight:android-driver:1.1.4"

If you only have an “app” module, then add it to that, but if you are in a multi-module project, I would highly suggest creating a “db” module (or similar) for this code.

8) Write your SQLDelight Android Code

In order to just show this working on Android, I pasted the code into the MainActivity, which is not what you should do, but it helps you validate that it’s actually working on Android.

You will need to use the AndroidSqliteDriver in order for SQLDelight to correctly write to the Android database. The JdbcSqliteDriver was helpful for allowing us to do in-memory unit testing, but it only keeps the database in memory, and would never save between app launches.

val androidSqlDriver = AndroidSqliteDriver(
    schema = Database.Schema,
    context = applicationContext,
    name = "items.db"
)

val queries = Database(androidSqlDriver).itemInCartEntityQueries

val itemsBefore: List = queries.selectAll().executeAsList()
Log.d("ItemDatabase", "Items Before: $itemsBefore")

for (i in 1..3) {
    queries.insertOrReplace(
        label = "Item $i",
        image = "https://localhost/item$i.png",
        quantity = i.toLong(),
        link = null
    )
}

val itemsAfter: List = queries.selectAll().executeAsList()
Log.d("ItemDatabase", "Items After: $itemsAfter")

9) Run The Code on Android

Hit the run button and filter Logcat so you can see that you have successfully added and retrieved data from SqlDelight on Android!

10) Peek at the “Magically” Generated Code

It’s cool to see where the plugin puts the code it generates in “build/sqldelight” and it may help you understand how SQLDelight works. The generated code is super easy to read since it uses Kotlin Data Classes, and the SQL code is just taken almost directly from your .sq file that you already wrote, but wrapped in a type-safe way.

Conclusion

These steps are all you need to get started with SQLDelight 1.x on Android.  Here is a pull request that contains all the changes mentioned in this post: https://github.com/handstandsam/SQLDelightQuickStart/pull/1/files.  At the time of writing this article 1.1.4 is the latest version.  Check out the SQLDelight change-log to see the latest released version.

Enjoy the beautiful generated Kotlin code which is generated from our .sq files, and enjoy validating your code via unit tests that can run without an Android device!

Related Links:

Sharing Gradle Configuration in Multi-Module Android Projects

Using multiple modules in our Android projects help us split apart our code into logical components.  They also can enable faster incremental builds, and more modular code.  One problem with multi-module projects is that there is a lot of verboseness of configuration.  This post shows you a method of sharing common configuration between your Android Library modules in order to cut down on boilerplate Gradle configuration.

I made this change in a PR in my ShoppingApp project on GitHub and ended up deleting a net 90 lines of code over 7 library modules.

apply from: “____.gradle”

You can add the contents of another Gradle file into your current one by using “apply from: ” and specifying the file whose content you want to add.

apply from: "$rootProject.projectDir/android-library.gradle"

$rootProject.projectDir

Modules can exist in different directory structures, so by leveraging the $rootProject.projectDir property, we specify paths based on the root project directory.

Original Library Module build.gradle

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'

android {
    compileSdkVersion Versions.compile_sdk

    defaultConfig {
        minSdkVersion Versions.min_sdk
        targetSdkVersion Versions.target_sdk
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
}

dependencies {
    implementation project(Modules.models)
    implementation Libs.kotlin_std_lib
}

Resulting Library Module build.gradle

apply from: "$rootProject.projectDir/android-library.gradle"

dependencies {
    implementation project(Modules.models)
    implementation Libs.kotlin_std_lib
}

Shared Gradle File

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'

android {
    compileSdkVersion Versions.compile_sdk

    defaultConfig {
        minSdkVersion Versions.min_sdk
        targetSdkVersion Versions.target_sdk
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
}

If You Do Something 3+ Times, Extract Out Functionality

Whenever it’s possible and makes sense, use common configuration to reduce boilerplate.  This same rule applies if you are writing code, or writing Android Gradle configuration.  This post shares an “easy win”, that you may be able to use to help better manage your multi-module project. There is so much more you can do to clean up your builds by leveraging buildSrc where you can write in Kotlin, Java or Groovy, but that’s for another post.

“It Depends” Is The Answer To Your Android Question

Android Questions:

  • Should I use Flutter? “It Depends”
  • Should I wrap a 3rd party library’s API? “It Depends”
  • Should I install the Android Q Beta? “It Depends”
  • Should I use Dagger? “It Depends”
  • Should I use Kotlin or Java? “It Depends”
  • Should I use React Native? “It Depends”
  • Should I use Dependency Injection? “It Depends”
  • Should I use OkHttp? “It Depends”
  • Should I use Multiple Activities or a Single Activity? “It Depends”
  • Should I upgrade to the latest Support Library? “It Depends”
  • Should I use a library that’s in Alpha? “It Depends”
  • Should I use Room or SqlDelight? “It Depends”
  • Should I write Espresso tests? “It Depends”
  • Should I bump my minSdk to 28? “It Depends”
  • Should I use MVP or MVVM or MVI or MVC? “It Depends”
  • Should I use RxJava or LiveData? “It Depends”
  • Should I learn Android or iOS? “It Depends”
  • Should I start a blog? “It Depends”
  • Should I start a side project? “It Depends”
  • … Insert Your Question Here  … “It Depends”

“It Depends” Is Technically Correct 💯% of the Time

While “It Depends” is technically correct since there is no absolute answer in software, it still doesn’t make it a good answer.  “Probably Should” is an answer well, but when you think about it, it’s still a variation of “It Depends”.

“It Depends” Is a Crappy Answer

Juhani brings up a great point about responsibility in his tweet above.  Opinions are great because they are shaped by experience.  As you gain experience, it’s important to share your opinions and discoveries because they will help provide insight and context into a topic.  That empowers the person searching for the answer to make a decision, because you can’t write software with “It Depends”, since it won’t compile. 😂

There Is No Perfect Answer

My goal of this post was to point out that there are tons of ways to do things, but based on your team, use case and target audience, there is no good 100% right answer for any topic.  I can strongly urge you to use Kotlin, but if you are building something that people are willing to pay millions of dollars from and they need Java, then Java is your right answer.  The important part is to keep listening to opinions and discoveries that are brought up, but know they are not a one-size-fits-all solution.

I’m happy to share my opinion and experiences with you on any topic if you reach out to me on Twitter @HandstandSam, and I’ll do my best not to answer with “It Depends”. 🙂

When You Should Use Null in Kotlin

I was recently reviewing code with a developer that is learning Kotlin and they were adamant that:

“You should never use null. Null is BAD.” 


Null has got a bad rap.  Yes, it’s to be avoided in most code, but in Kotlin, null is part of the type system and the compiler will tell you when you haven’t handled it appropriately.  However, just because it’s easy to identify null in Kotlin doesn’t mean we should use it everywhere.  There are perfectly appropriate safe uses of null in Kotlin.

Valid usages of null in Kotlin

1) When Representing “No Value”

 var user: User? = null

If you need a way to represent whether a value is initialized or whether it has no value, then null is appropriate in this case.

2) Consuming External Data Sources

If you need a way to represent whether a value is available or unavailable, then null is appropriate in this case as well.

Apps must consume external data sources that we don’t have full control over.  When operating in a non-hermetic environment, we run into cases where some data sources are not reliable and may provide null content.  Whether it is a REST API, or an Android System Service, representing data that may not be available as a nullable type is important because it allows us to create code paths to handle both cases.

Functional Purity

While it seems ideal to never have null in your code, it’s not always possible to avoid, and sometimes shouldn’t be avoided.

Using a Sealed Class to Avoid Using Null

sealed class UserWrapper {
  object UninitializedUser : UserWrapper()
  data class InitializedUser(val user: User): UserWrapper()
}

Creating a sealed class for the sole purpose of avoiding the use of null introduces unnecessary boilerplate code.

Don’t get me wrong, sealed classes are one of my favorite features of Kotlin though, and are great if you need to handle more scenarios than just initialized or uninitialized, but if that’s all you need, then using null is a valid approach.

Using a Nullable Field

val user : User?

Using a nullable field is much more concise in your definition than a sealed class.  It’s also more concise to use a ?. operator instead of an “if” or “when” statement to process your sealed class.

Offensive Programming

If you really want to, you can run around with a bunch of !! (double bangs) in your code.  However, you are living dangerously and your code will crash if the value is null.  This may be what you are looking for though if you are trying to follow practices of Offensive Programming.

//This will crash if the user is null
handleNonNullUser(user!!)

Defensive Programming has us cover all possible code paths just in case it might occur.  When you do have these extra code paths, provide some fallback logic or warning logs.

Ways of Handling Null

If you check once that the value is non-null, the Kotlin compiler is smart enough for you to write your code without providing any !!.  Then process the non-null val after it’s been checked once, to avoid multiple checks throughout my code. Here are some ways to do this:

Null Comparison 😐
if (user != null) {
  handleNonNullUser(user)
} else {
  Log.w(TAG, "user was null")
  handleNullUser(user)
}

This is very Java-esque, but it does the trick.

Let 🙂
user?.let {
  //Work with non-null user
  handleNonNullUser(user)
}

I like using let because it allows us to write much more idiomatic Kotlin.  It does not allow us to handle null, “else” case though.

Early Exit 👍
fun handleUser(user : User?) {
  user ?: return //exit the function if user is null
  //Now the compiler knows user is non-null
}

If the value is null, you can exit the method immediately, otherwise you can operate on the non-null value (because the Kotlin compiler is that smart).

Immutable Shadows 👥😲

Using immutable “variable shadows” a really cool way of providing null safety.  It will do an “Early Exit” if the value is null, otherwise it will assign the non-null value of the var to an immutable val allowing the compiler to know the value is non-null.  Thanks to Gabriel Peal for this tip!

var user : User? = null

fun handleUser() {
  val user = user ?: return //Return if null, otherwise create immutable shadow
  //Work with a local, non-null variable named user
}

Conclusion

There is no doubt that you will write better code if you try and stick with non-null and vals where you can. However, if you run into a scenario where using null is the right thing to do, then don’t fight it.

Code appropriately using one of the techniques I’ve shared in this article to handle null effectively.  These techniques allow you to avoid having to use the !! operator which can lead to NullPointerExceptions.  The whole point of having a nullable type in Kotlin is to allow you to avoid NullPointerExceptions at compile time, instead of them sneaking up on your at run time.

You may be thinking that this post is similar to Roman Elizarov’s post “Null is your friend, not a mistake“, and you would be right.  His post inspired me to finally publish this, and you can read more of the story behind publishing this post here.

Hitting Publish is the Hardest Part of Blogging

I had been sitting on the draft of my post “When You Should Use Null in Kotlin” since November (for 3 months) because after I had a colleague review it, I wasn’t sure if my views were valid.  My colleague told me about “null, the billion-dollar mistake” and asked if I was just trying to “stir the pot” with a possibly unpopular opinion. That made me question if my views were actually valid, so I didn’t hit “Publish”.

Draft was Last Modified 3 Months Ago

Validation

Earlier this month, Roman Elizarov (@relizarov), from the Kotlin libraries team posted an article which validated my thoughts I shared in my draft post, null is something to use, and not completely avoid:

I was excited to see a like-minded post from one of my software idols who designs the Kotlin language:

Chatting with Roman at Google I/O 2018

Thanks to this validation, I finally got up the courage to finish my post which took many hours and reviews, but I finally published my article. 😄 Thanks Roman (@relizarov)!

Non-null Opinions

I encourage you to share your opinion on topics where you have spent enough time digging into a topic to develop one.  So much of computer science is subjective, and there will always be varying opinions.  As long as you have identified reasons why you feel a certain way, those are valid.

It’s okay to share your thoughts.  Your opinion is non-null 😂.  Be humble enough to listen to others and allow yourself to use objective reasoning to help shape your understanding.

Leverage The Community

The Android community has varying opinions on many things, but that isn’t a bad thing.  There is no single way to do something, and whether or not something is the right solution depends on the use case, and the skills of the team.

Many members of the community are there to help.  I encourage you to reach out and ask for feedback from more than one person as it will help you get well rounded feedback.  Before I published the post I got feedback from @molsjeroen, @ataulm, @ZakTaccardi, @gpeal8 and @jarvisapps.  Each person had slightly different insights, and it helped me create a higher quality post.

A Checklist for Hitting Publish

  1. Write your content
  2. Add applicable content/images/code
  3. Review your content as if you were a reader
  4. Ask for reviews from 2+ people
  5. Address feedback
  6. Set a time limit (3? days)

I put together this checklist to help guide me in the future, and hope it will allow me to publish more posts!  I have at least 5 more drafts in my head that I need to get to next.  By publishing these articles, I’m able to get to the next one, and hopefully help someone publish theirs.

Why We Need “fat” AARs for Android Libraries

I want the ability to create a single (“fat”) AAR artifact from multiple Android Libraries (all from source).  Non-source, transitive dependencies will still be pulled in via a pom.xml file.

Requirements:

  1. I want to write and SDK that would be used by 3rd parties and possibly internal teams.  I want to write modular code on my side, with clean separation of concerns, yet only provide a single AAR artifact to users of my library.  Users of my library don’t need to know how I architected the internals, and in some cases I don’t want them to know.  I want to obfuscate my internal implementations to avoid accidental usage as well as for some security.
  2. I want to shrink and optimize my code with ProGuard (which is being replaced by R8) on my entire library, and generate only a single AAR file.  With current tooling, each module is only aware of its own code and resources when ProGuard is run.  This means that I can’t optimize or obfuscate my entire library/SDK in its entirety.  Because I must run ProGuard on each module individually at the current time, you end up with NoClassDefFoundErrors if you try to be aggressive with obfuscation.

The Use Case

For this post, think of an SDK you would get from an external vendor, or another team that contains their shrink-wrapped code that you need to plop into your app.  For an app like Twitter, that could mean:

  • Login page library
  • Video streaming player library
  • Home feed library
  • Emoji support library
  • etc.

Note: With the Twitter example I just mean to show that you can bundle discrete components of an app with clear boundaries between them.

When you get into a big app, you have to separate out components, and using Android Libraries to do this is a great decision.  That being said, I would never want “fat” AARs to be the only way to do things.  I just think it would solve some use cases when you are creating and SDK to be used by 3rd parties that don’t need to know how the internals of your code work.

Technical Reasons: Why Creating a “FAT” AAR Doesn’t Work

Apps/APKs can combine as many AARs into a single APK artifact.  That’s because there is a Manifest merge process that defines rules on how the AndroidManifest.xml, resources and assets are merged for the resulting APK file.  At the time the APK is created, ProGuard can be applied to optimize all byte code, remove unused classes, and perform code obfuscation.

Didn’t Someone Create a Library to Do This?

Kinda… A long time ago.  There was a partial workaround for manifest merging for Android Libraries using Android Gradle Plugin 2.x called “FAT” AAR, but it was limited, unofficial, and no longer works with Gradle 3.x.  There seems to be no plans to make it work with newer versions of Gradle.  It esentially tried to do its own hacky version of Manifest merging.

Argument Against: You only need to specify a single dependency in your build.gradle to import all of the transitive libraries. Why are you complaining?

This is true for the use case where you publish your artifacts correctly to a public Maven repository.  Your user would only need to care about adding a single Gradle dependency, and the others would be pulled down transitively.  All they would need to add is “com.example:my-lib:1.0.0” to their Gradle dependencies. This works great in a lot of cases, like the Android Support Library, where the dependencies are all published publicly, and users can cherry-pick the pieces they want.

In the use case I’m requesting this for, existing methods aren’t great for 2 reasons.

  1. I want to control what my shrink-wrapped artifacts look like, while still maintaining modularized code internally.  It’s easier to hand over a single AAR file when you need to distribute a library via a non-public Maven repository. Yes, I could ask users to create a file-based maven repository in the project, but that is ugly.
  2. I want to shrink and optimize all of my library before delivering it to users.  It is only possible to run ProGuard on each module individually at the current time, which means that code optimizations and obfuscation breaks when it is used aggressively on each module independently.

Finally

I’ve created this post to explain some of the current limits of building Android Libraries with the Android Gradle Plugin that I’ve run into, and to make a plea to the Android Tooling team to accept the issue for newer versions of Android Gradle Plugin.  ⬇Xavier Ducrohet, the Android SDK Tech Lead said this is being considered for Android Gradle Plugin 3.3, but isn’t on the roadmap yet.  Since 3.2 is almost out the door, I figured now is a good time to make a push for this issue.

If you have this same issue or use case, please ⭐ the issue, but also comment about how this uniquely effects your development.

Kotlin + buildSrc for Better Gradle Dependency Management

Multi-module Android projects are now the recommended way to take advantages of performance improvements with Android Gradle Plugin 3+.  However, as we add more modules to our project, we quickly run into the issue of dependency management.

Different ways of managing Gradle dependencies:
  1. Manual Management
  2. Google’s Recommendation using “ext”
  3. Kotlin + buildSrc

1) Manual Management 👎

This is the way most of us have been managing dependencies, but it requires a lot of manual changes whenever you upgrade a library to ensure that versions are updated correctly.

module_a/build.gradle

implementation "com.android.support:support-annotations:27.0.2"
implementation "com.android.support:appcompat-v7:27.0.2"
implementation "com.squareup.retrofit2:retrofit:2.3.0"
implementation "com.squareup.retrofit2:adapter-rxjava2:2.3.0"
implementation "io.reactivex.rxjava2:rxjava:2.1.9"

module_b/build.gradle

implementation "com.android.support:support-annotations:27.0.2"
implementation "com.android.support:appcompat-v7:27.0.2"
implementation "com.squareup.retrofit2:retrofit:2.3.0"
implementation "com.squareup.retrofit2:adapter-rxjava2:2.3.0"
implementation "io.reactivex.rxjava2:rxjava:2.1.9"

This is a lot of duplicated configuration that is hard to manage upgrades with, especially when you have a lot of modules.

2) Google’s Recommendation: Using Gradle Extra Properties 🙂

This is Google’s recommended way of doing this as seen in the Android documentation.  It is also used in lots of Android projects, like ButterKnife and Picasso.

This method is great for upgrading libraries like the support library.  Every support library dependency has the same version number, so only having to change this in one place is 💯.  The same things goes for Retrofit, and many other libraries.

Root-level build.gradle

ext {
  versions = [
    support_lib: "27.0.2",
    retrofit: "2.3.0",
    rxjava: "2.1.9"
  ]
  libs = [
    support_annotations: "com.android.support:support-annotations:${versions.support_lib}",
    support_appcompat_v7: "com.android.support:appcompat-v7:${versions.support_lib}",
    retrofit :"com.squareup.retrofit2:retrofit:${versions.retrofit}",
    retrofit_rxjava_adapter: "com.squareup.retrofit2:adapter-rxjava2:${versions.retrofit}",
    rxjava: "io.reactivex.rxjava2:rxjava:${versions.rxjava}"
  ]
}

module_a/build.gradle

implementation libs.support_annotations
implementation libs.support_appcompat_v7
implementation libs.retrofit
implementation libs.retrofit_rxjava_adapter
implementation libs.rxjava

module_b/build.gradle

implementation libs.support_annotations
implementation libs.support_appcompat_v7
implementation libs.retrofit
implementation libs.retrofit_rxjava_adapter
implementation libs.rxjava

This is a huge step ahead from manual management, but IDE support is lacking.  Check out this screencast of migrating to use Gradle Extra Properties (“ext”), and this Github pull request of the results.

While you can be content with using “ext” properties, I think you will be excited to use Kotlin in a buildSrc directory.

3) Kotlin + buildSrc == Android Studio Autocomplete 😎 🎉

You can create a buildSrc module with Kotlin code to manage dependencies and get IDE completion support.

From the Gradle Documentation:

When you run Gradle, it checks for the existence of a directory called buildSrc. Gradle then automatically compiles and tests this code and puts it in the classpath of your build script. You don’t need to provide any further instruction.

You just need 2 files in your buildSrc module:

  1. build.gradle.kts
  2. Kotlin Code (In this case,Dependencies.kt)

buildSrc/build.gradle.kts

plugins {
    `kotlin-dsl`
}

buildSrc/src/main/java/Dependencies.kt

object Versions {
    val support_lib = "27.0.2"
    val retrofit = "2.3.0"
    val rxjava = "2.1.9"
}

object Libs {
 val support_annotations = "com.android.support:support-annotations:${Versions.support_lib}"
 val support_appcompat_v7 = "com.android.support:appcompat-v7:${Versions.support_lib}"
 val retrofit = "com.squareup.retrofit2:retrofit:${Versions.retrofit}"
 val retrofit_rxjava_adapter = "com.squareup.retrofit2:adapter-rxjava2:${Versions.retrofit}"
 val rxjava = "io.reactivex.rxjava2:rxjava:${Versions.rxjava}"
}

After we have done a Gradle Sync, following making the changes above, we can now access any of the values in Android Studio.

The result looks very similar to what “ext” looked like, but we have autocomplete and click support (to take you to the definition).

module_a/build.gradle

implementation Libs.support_annotations
implementation Libs.support_appcompat_v7
implementation Libs.retrofit
implementation Libs.retrofit_rxjava_adapter
implementation Libs.rxjava

module_b/build.gradle

implementation Libs.support_annotations
implementation Libs.support_appcompat_v7
implementation Libs.retrofit
implementation Libs.retrofit_rxjava_adapter
implementation Libs.rxjava

Check out this screencast and this Github pull request showing migration from Gradle Extra Properties “ext” to use Kotlin + buildSrc.

Conclusion

I highly recommend the “Kotlin + buildSrc” option.  It may not seem like it’s that big of a deal, but managing Gradle dependencies is a pain, and having autocomplete and click support is a game changer.  No more switching back and forth between files manually!

Related Caster.io Lessons on Gradle Dependency Management (FREE)

  1. Gradle Dependency Management: Using Gradle Extra Properties (ext)

  2. Gradle Dependency Management: Using Kotlin and buildSrc for build.gradle Autocomplete in Android Studio

Related Links

Hat Tips/Thanks

Questions/Comments?

Reach out to me on Twitter at @HandstandSam

AnDevCon 2017 – How Yahoo Finance Scales on Android – Vikram Bodicherla

I saw Vikram‘s talk at Droidcon NYC 2016 talk about app performance, and wanted to make sure I made it to his talk.  He talks about overall processes for a successful development team along with tools and tips for shipping apps.

Developers shouldn’t be afraid to dip your toes into “product”.
Contribute to feature definition to make your voice heard as a user and for technical implementation.

Understanding your users – Fantasy Football Example:
You should be aware of who is using your app. You might think everyone using a fantasy football app are very serious users, but we find that 12% randomly pick, and 60% are first year users. Try to find patterns between different types of users of your app. Build personas of your users. Building personas of your users is a way to explain behavior that would be hard to explain otherwise. Give these personas name and put them up on the wall in your office. Know who your users are and design for them.

Personas for fantasy football includes:

  • Seasoned pros
  • People that are forced to join by their friends
  • People that are serious, but learning
  • “average” users

Data Driven Decisions via Experiments:
DAUs and Downloads are really “Vanity Metrics”, since they don’t gain a ton of insight. Data driven insights are real; not opinions. Wrong decisions can be validated quickly, so feel empowered to test, measure, and grow. Instead of doing costly user research, you can push something to a small group of users, and gain data there vs. expensive user research.

Each experiment should have:

  • A hypothesis
  • An owner
  • A deadline for the end of the experiment.
  • Planned removal of the code from your app. You learned something from it, now “Let it go!!!”

Scrum
Planning is a good investment. You can see how long things will take, determine dependencies, and people can show interest in pieces of the work.  Agile is important because it’s not adverse to change like Waterfall is.

Types of stories in Scrum:

  • User story
  • Engineering story

Scrum story checklist:

  • Clear definition
  • Acceptance criteria
  • Edge cases and error scenarios
  • Analytics
  • Animations and design

Grooming

  • should be (1x/week for 1 hour)
  • It helps the team to understand stories -> Determine level of effort for stories (Points)
  • Stories should have reasonable detail. Be very critical and make sure the story is well defined.
  • Don’t get hung up on one story. If your getting hung up, move on and take that offline so you don’t waste your entire grooming on one thing.
  • NEVER write stories during Grooming.
  • NEVER point a story that doesn’t have all the details.

If you get roll-over and carry-over after a sprint consistently, you’re doing something wrong and should revisit your processes.

Daily stand-ups should be no greater than 10 minutes and should provide high level updates. Low level updates should be taken “offline”, or “parking lotted”.

At the end of the sprint, you can hold a retrospective and demo completed stories.  Please prepare up front for this so we don’t have to wait for you to launch the emulator or recompile your project.

“If you’re are not practicing scrum in sprit, you are better off not doing it.”

Continuous Delivery

  • Minimizing the time between “code complete” and “deployable”
  • deployable != deploy
  • This can only be achieved with continuous integration (CI)
  • If you do deploy immediately to your users, you get immediate feedback, but not always the best for your users. Vikram recommend every 2 weeks on average, but depends.
  • Have internal alpha and beta programs for internal users to try the app before it goes to production.

Pull Request (PR) Tools

  • facebook/mention-bot – Can tag reviewers based on “git blame” history
  • SonarCube
  • https://codecov.io for Code Coverage
  • Danger -> Keep PRs <500 lines, PR message should be >25 chars.
  • Emulator in an iframe, running the code in the PR.  -> https://appetize.io Removes need to compile and install.

APK storage and deployment:

Culture

  • How you act/think/interact. Keep high standards, because you are what your lowest standard is.
  • Ownership is important. Communicate deviations and compromises so it’s not lost. Proactively check app quality issues and triage as soon as you can.
  • Set goals, but aim for 70%. If you get 100%, then your goals are not high enough.

Meeting etiquite

  • Everyone needs to have value, or they shouldn’t be there
  • Reject meetings if they are not needed
  • Meeting owner should have adgenda, goals and come out with action items.
  • There should be a hard start and end type.

Code is a liability. Once it’s out there, you have to support it. Changing code is expensive.  Deleting code is a good thing.

Feature Flags – Client-side feature flags are important, along with remote feature flags.  Client-side flags should take priority, but if it’s on, then use the remote flag.

AnDevCon 2017 – A Room With a ViewModel – Mark Murphy (CommonsWare)

Word of the day: “Transmogrify”
“to transform, especially in a surprising or magical manner.”

Mark draws a great comparison between Room and Retrofit as they both use annotation processing, and describe either a URL path, or a DB query.  The @Query annotation in Room, is similar to the path in Retrofit that is provided to @GET, @POST, etc.

Parameters can be sent with the syntax :postalCodes.  You can pass parameters into a query this way:

@Query(“SELECT * FROM Customer WHERE postalCode IN (:postalCodes)”)
List<Customer> findCustomersInPostalCodes(String… postalCodes)

Cool DB Testing Tip for Android Instrumentation Tests: In-memory databases work the same way that SQLite databases do that are saved to the disk. In-memory database are great for instrumentation tests because they are fast, and when you are done with it, it’s gone from memory, and doesn’t persist to disk.  It’s not recommended to use in-memory databases in true client apps however.

Types used in Room need a @TypeConverter.  You can specify the type converters to be used in the following way:

@TypeConverters({TypeConverter.class})

Caveats about relations:
You can use @ForeignKey on a child, but… <OMG head explosion />.  Foreign keys are there, but there aren’t any magical methods generated to retrieve a child. You can just get an ID for the child, and then have to re-query for that. You can specify cascading deletes however which is useful.

Room Migrations – Create instances of Migration –  A little more sane than just plain SQLite.

Note about SQLCipher – It was last updated in 2009, and the APIs are really hard (if not impossible) to integrate with Room.

LiveData – Room works really well with Rx programming. 🙂

Predictions: We will go through a lot of iterations of the APIs as kinks are worked out and things stabilized.  The guess is that a final version would be available around Google I/O 2018.

Check out Mark Murphy on the internet:

AnDevCon 2017 – An Introduction to RxJava – Matt Dupree

Here are some notes I took from Matt Dupree’s talk.  It was a really great intro to Rx, and done in a different way than most Rx talks I’ve seen.  He creates mental building blocks to get us from the Java Array to the Rx Observable.

“We are missing an abstraction”
Array -> Iterable -> Sequence -> Observable

Goal of this talk: Escape from “Callback Hell” (Too many nested callbacks, and Observables are here to help).

In Java, the “Iterable” interface allow us to abstract away from an Array, hiding us from the underlying implementation like LinkedList, HashSet, etc.  We just care that we are going through the items when we have an Iterable, and don’t really car how it’s done.

A button clicks example used:
* If you knew all your button clicks up front, you’d just do a “for” loop
* Instead you have an onClickListener since you don’t know when it’ll happen
* You instead subscribe to an observable stream (which looks like a loop), and for each observable event, you perform the action.

Interesting point: With an observable, data is not in memory necessarily, but you write code like it is.  This is another layer of abstraction that is helpful in doing delcarative programing instead of imperative programming.

Declarative Programming
This is “WHAT” I want to happen.

vs.

Imperative Programming
This is “HOW” I want it to happen.

Cool tip about “Debouncing”: I hadn’t heard of this before, but he shows another use case regarding a search text box, and he showed how EASY it was to use debouncing.  Debouncing can help you wait for the stream to settle, and in this case you can wait 300ms after the last event. You can just say wait until the observable hasn’t been called in XXX milliseconds, and if that’s the case, then continue on.

Resources:

Note: “Rx” means Reactive Extensions. (I, personally hear the term “Rx” so much, that I forget that it means something else sometimes)