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.
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:
AssetPackManager_showCellularDataConfirmation()AssetPackManager_getShowCellularDataConfirmationStatus()
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: UseAssetPackLocation_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.