The Google Play Instant Plugin for Unity Beta simplifies conversion of a Unity-based Android app into an instant app that can be deployed through Google Play Instant.

The plugin’s Unity Editor (IDE) features include:

• The option to switch between Installed and Instant build modes.
• A centralized view of Android Player Settings that should be changed to support Google Play Instant.
• An action to build the instant app for publishing on Google Play Console.
• An action to build and run the instant app on an adb connected Android device.

The plugin’s Unity Engine (runtime) features include:

• A method for displaying a Play Store dialog to install the full version of the instant app.

• Unity 5.6, 2017.4, or 2018.2.
  • Note: other versions may work, but are not tested regularly.
• A device running Android 5.0 (Lollipop) or newer.

• Obtain the latest .unitypackage from the releases page.
• Import the .unitypackage by clicking the Unity IDE menu option Assets > Import package > Custom Package and importing all items.

After import there will be a “PlayInstant” menu in Unity providing several options described below.

Opens a window that enables switching between "Installed" and "Instant" development modes. Switching to "Instant" performs the following changes:

• Creates a Scripting Define Symbol called PLAY_INSTANT that can be used for scripting with #if PLAY_INSTANT / #endif.
• Provides a text box for optionally entering an "Instant Apps URL" that is used to launch the instant app.
  • If a URL is provided, you will need verify ownership of the domain by Configuring Digital Asset Links.
  • If a URL is not entered, a URL will be provided for you at https://instant.apps/your.package.name.
• Manages updates to the AndroidManifest.xml for certain required changes such as android:targetSandboxVersion.

The Play Instant Build Settings window also provides control over the scenes included in the build:

• By default the scenes included in the build are the enabled scenes from Unity's "Build Settings" window.
• The scenes included in the build can be customized via a comma separated list of scene names.
• Scenes that are not included in the build, but that are loaded via Asset Bundles, may have required components removed by engine stripping. Specify the path to an Asset Bundle Manifest file to retain these required components.

Opens a window that lists Android Player Settings that should be changed to make the app Google Play Instant compatible. These are divided into Required and Recommended settings. Click on an “Update” button to change a setting.

Installs or updates the “Instant Apps Development SDK” using sdkmanager. The plugin requires SDK version 1.2 or higher. If there is a license that needs to be accepted, the plugin will prompt for acceptance.

Google Play Console requires that the APKs for an instant app are published together in a ZIP file. Although most Unity instant apps will consist of a single APK, the requirement holds. This menu option performs a build and stores the resulting APK in a ZIP file suitable for publishing.

This option runs the instant app on an adb connected device by performing the following steps:

• Verifies that required Unity Build Settings and Android Player Settings are configured correctly.
• Invokes Unity's BuildPlayer method to create an APK containing all scenes that are currently enabled in “Build Settings”.
• If the connected device is running an Android version before 8.0 (Oreo), provisions the device for Instant App development by installing "Google Play Services for Instant Apps" and "Instant Apps Development Manager" (only if not done already).
• Runs the APK as an instant app on the adb connected device.

The goal of many instant apps is to give users a chance to experience the app before installing the full version. The plugin provides methods for transferring state from instant to installed app and for displaying a Play Store install dialog. These methods are also available via Google Play Services Java APIs, but the plugin's C# implementations are easier to use in Unity.

An instant app with an "Install" button can display a Play Store install dialog by calling the following from an install button click handler:

GooglePlayInstant.InstallLauncher.ShowInstallPrompt();

The ShowInstallPrompt() method has an overload that allows for one or more of the following:

• Determining if the user cancels out of the installation process. Override onActivityResult() in the instant app's main activity and check for RESULT_CANCELED on the specified requestCode.
• Passing an install referrer string via the referrer parameter.
• Passing state about the current game session via PutPostInstallIntentStringExtra().

These are demonstrated in the following example:

const int requestCode = 123;
var sessionInfo = /* Object serialized as a string representing player's current location, etc. */;
using (var activity = GooglePlayInstant.UnityPlayerHelper.GetCurrentActivity())
using (var postInstallIntent = GooglePlayInstant.InstallLauncher.CreatePostInstallIntent(activity))
{
    GooglePlayInstant.InstallLauncher.PutPostInstallIntentStringExtra(postInstallIntent, "sessionInfo", sessionInfo);
    GooglePlayInstant.InstallLauncher.ShowInstallPrompt(activity, requestCode, postInstallIntent, "test-referrer");
}

If the user completes app installation, the Play Store will re-launch the app using the provided postInstallIntent. The installed app can retrieve a value set in the postInstallIntent using the following:

var sessionInfo = GooglePlayInstant.InstallLauncher.GetPostInstallIntentStringExtra("sessionInfo");

Notes:

• The extras included in the postInstallIntent may not reach the installed app if the user installs the app but cancels the post-install launch. Passing intent extras is better suited for retaining active session state than it is for retaining persistent state; for the latter refer to the Cookie API.
• Anyone can construct an intent with extra fields to launch the installed app, so if the payload grants something of value, design the payload so that it can only be used once, cryptographically sign it, and verify the signature on a server.

The Cookie API provides methods for passing a "cookie" (e.g. player ID or level completion data) from an instant app to its corresponding installed app. Unlike postInstallIntent extras, the "cookie" state is available even if the user doesn't immediately launch the installed app. For example, an instant app could call the following code from an install button click handler:

var playerInfo = /* Object serialized as a string representing game levels completed, etc. */;
var cookieBytes = System.Text.Encoding.UTF8.GetBytes(playerInfo);
try
{
    var maxCookieSize = GooglePlayInstant.CookieApi.GetInstantAppCookieMaxSize();
    if (cookieBytes.Length > maxCookieSize)
    {
        UnityEngine.Debug.LogErrorFormat("Cookie length {0} exceeds limit {1}.", cookieBytes.Length, maxCookieSize);
    }
    else if (GooglePlayInstant.CookieApi.SetInstantAppCookie(cookieBytes))
    {
        UnityEngine.Debug.Log("Successfully set cookie. Now display the app install dialog...");
        GooglePlayInstant.InstallLauncher.ShowInstallPrompt();
    }
    else
    {
        UnityEngine.Debug.LogError("Failed to set cookie.");
    }
}
catch (GooglePlayInstant.CookieApi.InstantAppCookieException ex)
{
    UnityEngine.Debug.LogErrorFormat("Failed to set cookie: {0}", ex);
}

If the user completes app installation, the installed app can retrieve the cookie data using the following code:

var cookieBytes = GooglePlayInstant.CookieApi.GetInstantAppCookie();
var playerInfoString = System.Text.Encoding.UTF8.GetString(cookieBytes);
if (!string.IsNullOrEmpty(playerInfoString))
{
    // Initialize game state based on the cookie, e.g. skip tutorial level completed in instant app.
}

• If the Unity project has an existing AndroidManifest.xml with multiple VIEW Intents on the main Activity and if an Instant Apps URL is provided, the plugin doesn't know which Intent to modify. This can be worked around by not providing an Instant Apps URL or by manually updating the manifest file.