Integrate asset delivery (native)

Use the steps in this guide to access your app’s asset packs from your C and C++ code. If you haven't built an app bundle with asset packs, see Build for native or Java before going further.

Sample integration code is available on GitHub.

Overview

The Play Core Native SDK provides the C header file play/asset_pack.h for requesting asset packs, managing downloads, and accessing the assets. You implement this API according to the delivery type of the asset pack you wish to access. These steps are shown in the following flowchart.

Asset pack flow diagram for native code

Figure 1. Flow diagram for accessing asset packs

Install-time delivery

Asset packs configured as install-time are immediately available at app launch. Use the NDK AAssetManager API to access assets served in this mode:

#include <android/asset_manager.h>
#include <android_native_app_glue.h>
...
AAssetManager* assetManager = app->activity->assetManager;
AAsset* asset = AAssetManager_open(assetManager, "asset-name", AASSET_MODE_BUFFER);
size_t assetLength = AAsset_getLength(asset);
char* buffer = (char*) malloc(assetLength + 1);
AAsset_read(asset, buffer, assetLength);

Fast-follow and on-demand delivery

The following sections show how to initialize the API, how to get information about asset packs before downloading them, how to call the API to start the download, and how to access the downloaded packs. These sections apply to fast-follow and on-demand asset packs.

App launch

Always call AssetPackManager_init() to initialize the asset pack API before calling any other function. Check for any asset pack error codes.

#include "play/asset_pack.h"
...
AssetPackErrorCode AssetPackManager_init(JavaVM* jvm, jobject android_context);

Also be sure to call the following functions in the onPause() and onResume() of ANativeActivityCallbacks:

Get download information about asset packs

Apps are required to disclose the size of the download before fetching the asset pack. Use the AssetPackManager_requestInfo() function to start an asynchronous request for the size of the download and whether the pack is already downloading. Then use AssetPackManager_getDownloadState() to poll for the download state (for example, call this function once per frame in your game loop). If a request fails, check the asset pack error codes.

AssetPackErrorCode AssetPackManager_requestInfo();      // Call once
AssetPackErrorCode AssetPackManager_getDownloadState(); // Call once per frame in your game loop

The AssetPackManager_getDownloadState() function returns the opaque type AssetPackDownloadState as an output pointer. Use this pointer to call the following functions:

AssetPackDownloadState* state;
AssetPackErrorCode error_code = AssetPackManager_getDownloadState(asset-pack-name, &state);
AssetPackDownloadStatus status = AssetPackDownloadState_getStatus(state);
uint64_t downloadedBytes = AssetPackDownloadState_getBytesDownloaded(state);
uint64_t totalBytes = AssetPackDownloadState_getTotalBytesToDownload(state));
AssetPackDownloadState_destroy(state);

Install

Use AssetPackManager_requestDownload() to start downloading an asset pack for the first time or to request for an asset pack update to complete:

AssetPackErrorCode AssetPackManager_requestDownload();  // Call once
AssetPackErrorCode AssetPackManager_getDownloadState(); // Call once per frame in your game loop

The AssetPackManager_getDownloadState() function returns the opaque type AssetPackDownloadState. For information on how to use this type, see Get download information.

Large downloads

If the download is larger than 150MB and the user is not on Wi-Fi, the download does not start until the user explicitly gives their consent to proceed with the download using a mobile data connection. Similarly, if the download is large and the user loses Wi-Fi, the download pauses and explicit consent is required to proceed using a mobile data connection. A paused pack has state WAITING_FOR_WIFI. To trigger the UI flow to prompt the user for consent, use the following:

Access asset packs

You can access an asset pack using file system calls after the download request reaches the COMPLETED state. Each asset pack is stored in a separate directory in the app's internal storage. Use AssetPackManager_getAssetPackLocation() to get an AssetPackLocation for the specified asset pack. Use AssetPackLocation_getStorageMethod() on that location to determine the storage method:

  • ASSET_PACK_STORAGE_APK: The asset pack is installed as an APK. See Install-time delivery to access these assets.
  • ASSET_PACK_STORAGE_FILES: Use AssetPackLocation_getAssetsPath() to get a file path to the directory containing the assets, or null if the assets have not been downloaded. Do not modify downloaded files in this file path.
AssetPackLocation* location;

AssetPackErrorCode error_code = AssetPackManager_getAssetPackLocation(asset-pack-name, &location);

if (error_code == ASSET_PACK_NO_ERROR) {
    AssetPackStorageMethod storage_method = AssetPackLocation_getStorageMethod(location);
    const char* assets_path = AssetPackLocation_getAssetsPath(location);
    AssetPackLocation_destroy(location);
}

Once you locate the assets, use functions like fopen or ifstream to access the files.

Other Play Core API methods

The following are some additional API methods you may want to use in your app.

Cancel request

Use AssetPackManager_cancelDownload() to cancel an active asset pack request. Note that this request is a best-effort operation.

Request removal

Use AssetPackManager_requestRemoval() to schedule the removal of an asset pack.

Next step

Test Play Asset Delivery locally and from Google Play.