Hi I am new in Android development and my app is completely database oriented. In my app I am using the method of copying a database file from the assets folder. It will increase the size of the apk.
I want to copy it from the internet the first time my app runs on the phone.
How do I download the database file to my app database folder.
This is how I did it:
I have an implementation of DownloadManager that deals with downloading the DB. In my case the DB is significantly big so DownloadManager is a good option for effectively dealing with large downloads.
One thing to note when implementing DownloadManager; It's recommended that you download files first as temporary files and then move them to the final location. This is to avoid weird security issues I faced when doing so. Also download notification visibility may affect what permissions are required, if you decide to have no notifications at all you need to add a DOWNLOAD_WITHOUT_NOTIFICATION.
Permissions required:
<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE " />
DownloadManager implementation
/**
* Manages all DB retrieval and file level validation.
*
*/
class DataBaseInitializationRepository(private val app: Application, private val dbHelper: DatabaseFileHelper) {
fun initiateDB( callback: DownloadCompleteCallback){
val dbUrl = dbHelper.getDbUrl()
val tempDbFile = dbHelper.getTempDbFile()
val permanentDbFile = dbHelper.getPermanentDbFile()
if (!permanentDbFile.exists() && tempDbFile.length() <= 0) {
val downloadManager = app.getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager
val downLoadDBRequest = DownloadManager.Request(Uri.parse( dbUrl ))
.setTitle( app.getString( R.string.download_db_title ) )
.setDescription(app.getString( R.string.download_db_description ))
.setDestinationInExternalFilesDir( app,
null,
tempDbFile.path
)
.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED)
val downloadId = downloadManager.enqueue( downLoadDBRequest )
registerReceiver( callback, downloadId )
}else{
callback.onComplete(0L)
}
}
private fun registerReceiver(callback: DownloadCompleteCallback, downloadId: Long){
val receiver = object: BroadcastReceiver(){
override fun onReceive(context: Context?, intent: Intent?) {
val id = intent?.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1)
if (id == downloadId){
//Move index reads to reusable function
val downloadManager = app.getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager
val query = DownloadManager.Query()
query.setFilterById( downloadId )
val data = downloadManager.query( query )
if(data.moveToFirst() && data.count > 0){
val statusIndex = data.getColumnIndex(DownloadManager.COLUMN_STATUS)
val status = data.getInt( statusIndex )
if(status == DownloadManager.STATUS_SUCCESSFUL){
val localUriIndex = data.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI)
val localFile = File(
data.getString( localUriIndex )
.replace("file://","" )
)
if(localFile.exists()){
permanentlyStoreDb(localFile)
callback.onComplete(id)
}else{
callback.onFail("Initial Database Download Failed - File not found")
}
}else if(status == DownloadManager.STATUS_FAILED){
val reasonIndex = data.getColumnIndex(DownloadManager.COLUMN_REASON)
val reason = data.getInt( reasonIndex )
if(reason == DownloadManager.ERROR_FILE_ALREADY_EXISTS){
callback.onComplete(id)
}else{
callback.onFail("Initial Database Download Failed: $reason")
}
}
}else{
callback.onFail("Initial Database Download Failed - Unable to read download metadata")
}
}
}
}
app.registerReceiver( receiver, IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE) )
}
private fun permanentlyStoreDb(tempFile: File): File {
val permanentDbFile = dbHelper.getPermanentDbFile()
try {
if(tempFile.exists()) {
tempFile.copyTo(
permanentDbFile,
true,
1024
)
tempFile.delete()
}else{
throw IOException("Temporal DB file doesn't exist")
}
}catch (ioex: IOException) {
throw IOException("Unable to copy DB to permanent storage:", ioex)
}
return permanentDbFile
}
/**
* Allows download completion to be notified back to the calling view model
*/
interface DownloadCompleteCallback{
fun onComplete(downloadId: Long)
fun onFail(message: String)
}
}
DatabaseFileHelper contains the logic to determine the temporary file, the permanent DB location and the DB URL where the download will happen. This is the logic I used for the temporary file:
fun getTempDbFile(): File {
return File.createTempFile(<FILE-LOCATION>, null, app.cacheDir)
}
So in case you want to notify a running Activity/Fragment, you only need to pass a DownloadCompleteCallback implementation to this component to get it.
In case you are using Room, just make sure your implementation of RoomDatabase uses the following on your getInstance method
.createFromFile( dbFileHelper.getPermanentDbFile() )
