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This tutorial describes the usage of the AutoValue library for creating value objects. It also overs AutoValue extensions, e.g, to convert to Parcelable.

1. Using AutoValue and its extensions

Auto is collection of code generators that automate certain repetitive tasks, like creating value objects. The tools create the code you would have written, but without the bugs.

1.1. AutoValue

AutoValue allows the creation of immutable value objects. Value objects are classes which treat any two instances with suitably equal field values as interchangeable.

1.2. Using AutoValue on Android

Auto-Value annotations allows to use AutoValue on Android.

Add the following dependencies to your build.gradle file.

dependencies {
    annotationProcessor 'com.google.auto.value:auto-value:1.4'
    provided 'com.jakewharton.auto.value:auto-value-annotations:1.4'
}

1.3. How to use AutoValue

In AutoValue you write an abstract class, and AutoValue implements it. You can provide a create method which allows you to return the generated instance of the class.

package com.vogella.android.autovalue;


import com.google.auto.value.AutoValue;

@AutoValue public abstract class Task {

    public abstract long id();
    public abstract String summary();
    public abstract String description();

    public static Task create(long id, String summary, String description) {
        return new AutoValue_Task(id, summary, description);
    }
}

1.4. Using Builder

Autovalue allows allows to create a Builder API.

package com.vogella.android.butterknifeexample;


import com.google.auto.value.AutoValue;

@AutoValue public abstract class Task {

    public abstract long id();
    public abstract String summary();
    public abstract String description();


    static Builder builder() {
        return new AutoValue_Task.Builder();
    }

    @AutoValue.Builder
    abstract static class Builder {
        abstract Builder setId(long value);
        abstract Builder setSummary(String value);
        abstract Builder setDescription(String value);
        abstract Task build();
    }
}

1.4.1. AutoValue extensions

The AutoValue extensions allows to support things like:

  • Parcelable

  • Json

  • Moschi

  • Gson

For example, to make an object Parcelable you simple add the following dependency to your build file.

annotationProcessor 'com.ryanharter.auto.value:auto-value-parcel:0.2.5'

2. Exercise: Use auto-value-parcel to create a Parcelable for Android

In this exercise you learn how to use the auto-value library and its extensions to implement Parcelable. Create or continue to use an Android project with the com.vogella.android.usinglibs top-level package.

2.1. Create second activity

Create a second activity and allow to start it from the first activity via a button click.

2.2. Using Auto-Value

Add the following dependencies to your app/build.gradle file.

dependencies {
    annotationProcessor 'com.google.auto.value:auto-value:1.4'
    annotationProcessor 'com.ryanharter.auto.value:auto-value-parcel:0.2.5'
    provided 'com.jakewharton.auto.value:auto-value-annotations:1.4'
}

Create a value object using auto-value.

package com.vogella.android.usinglibs;


import android.os.Parcelable;

import com.google.auto.value.AutoValue;

@AutoValue public abstract class Task implements Parcelable{

    public abstract long id();
    public abstract String summary();
    public abstract String description();

    public static Task create(long id, String summary, String description) {
        return new AutoValue_Task(id, summary, description);
    }
}

Pass the Task object to the second activity, as intent parameter.

Intent intent = new Intent(this, SecondActivity.class);
Task task = Task.create(1,"hello","Testing");
intent.putExtra("task", task);
startActivity(intent);

In the second activity, display the Task you received via the Intent.

2.3. Optional: Switch to a builder API

Change your code to generate a builder API for your Task. Define a static abstract class called builder and define a builder API with the @AutoValue.Builder annotation.

Change your code which passed the intent to the second activity.

Intent intent = new Intent(this, SecondActivity.class);
Task task = Task.builder().setId(1).setSummary("hello").setDescription("Testing").build();
intent.putExtra("task", task);
startActivity(intent);

The following shows a possible solution.

package com.vogella.android.usinglibs;


import android.os.Parcelable;

import com.google.auto.value.AutoValue;

@AutoValue public abstract class Task implements Parcelable{

    public abstract long id();
    public abstract String summary();
    public abstract String description();

    static Builder builder() {
        return new AutoValue_Task.Builder();
    }
    @AutoValue.Builder
    abstract static class Builder {
        abstract Builder setId(long value);
        abstract Builder setSummary(String value);
        abstract Builder setDescription(String value);
        abstract Task build();
    }

}

3. About this website

4. AutoValue resources

4.1. vogella GmbH training and consulting support

TRAINING SERVICE & SUPPORT

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The vogella company offers expert consulting services, development support and coaching. Our customers range from Fortune 100 corporations to individual developers.

Copyright © 2012-2016 vogella GmbH. Free use of the software examples is granted under the terms of the EPL License. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.

See Licence.